FreeBSD/Linux Kernel Cross Reference
sys/kernel/cpuset.c

     /*
      *  kernel/cpuset.c
      *
      *  Processor and Memory placement constraints for sets of tasks.
      *
      *  Copyright (C) 2003 BULL SA.
      *  Copyright (C) 2004-2007 Silicon Graphics, Inc.
      *  Copyright (C) 2006 Google, Inc
      *
     *  Portions derived from Patrick Mochel's sysfs code.
     *  sysfs is Copyright (c) 2001-3 Patrick Mochel
     *
     *  2003-10-10 Written by Simon Derr.
     *  2003-10-22 Updates by Stephen Hemminger.
     *  2004 May-July Rework by Paul Jackson.
     *  2006 Rework by Paul Menage to use generic cgroups
     *  2008 Rework of the scheduler domains and CPU hotplug handling
     *       by Max Krasnyansky
     *
     *  This file is subject to the terms and conditions of the GNU General Public
     *  License.  See the file COPYING in the main directory of the Linux
     *  distribution for more details.
     */
    
    #include <linux/cpu.h>
    #include <linux/cpumask.h>
    #include <linux/cpuset.h>
    #include <linux/err.h>
    #include <linux/errno.h>
    #include <linux/file.h>
    #include <linux/fs.h>
    #include <linux/init.h>
    #include <linux/interrupt.h>
    #include <linux/kernel.h>
    #include <linux/kmod.h>
    #include <linux/list.h>
    #include <linux/mempolicy.h>
    #include <linux/mm.h>
    #include <linux/memory.h>
    #include <linux/export.h>
    #include <linux/mount.h>
    #include <linux/namei.h>
    #include <linux/pagemap.h>
    #include <linux/proc_fs.h>
    #include <linux/rcupdate.h>
    #include <linux/sched.h>
    #include <linux/seq_file.h>
    #include <linux/security.h>
    #include <linux/slab.h>
    #include <linux/spinlock.h>
    #include <linux/stat.h>
    #include <linux/string.h>
    #include <linux/time.h>
    #include <linux/backing-dev.h>
    #include <linux/sort.h>
    
    #include <asm/uaccess.h>
    #include <linux/atomic.h>
    #include <linux/mutex.h>
    #include <linux/workqueue.h>
    #include <linux/cgroup.h>
    
    /*
     * Workqueue for cpuset related tasks.
     *
     * Using kevent workqueue may cause deadlock when memory_migrate
     * is set. So we create a separate workqueue thread for cpuset.
     */
    static struct workqueue_struct *cpuset_wq;
    
    /*
     * Tracks how many cpusets are currently defined in system.
     * When there is only one cpuset (the root cpuset) we can
     * short circuit some hooks.
     */
    int number_of_cpusets __read_mostly;
    
    /* Forward declare cgroup structures */
    struct cgroup_subsys cpuset_subsys;
    struct cpuset;
    
    /* See "Frequency meter" comments, below. */
    
    struct fmeter {
            int cnt;                /* unprocessed events count */
            int val;                /* most recent output value */
            time_t time;            /* clock (secs) when val computed */
            spinlock_t lock;        /* guards read or write of above */
    };
    
    struct cpuset {
            struct cgroup_subsys_state css;
    
            unsigned long flags;            /* "unsigned long" so bitops work */
            cpumask_var_t cpus_allowed;     /* CPUs allowed to tasks in cpuset */
            nodemask_t mems_allowed;        /* Memory Nodes allowed to tasks */
    
            struct cpuset *parent;          /* my parent */
    
           struct fmeter fmeter;           /* memory_pressure filter */
   
           /* partition number for rebuild_sched_domains() */
           int pn;
   
           /* for custom sched domain */
           int relax_domain_level;
   
           /* used for walking a cpuset hierarchy */
           struct list_head stack_list;
   };
   
   /* Retrieve the cpuset for a cgroup */
   static inline struct cpuset *cgroup_cs(struct cgroup *cont)
   {
           return container_of(cgroup_subsys_state(cont, cpuset_subsys_id),
                               struct cpuset, css);
   }
   
   /* Retrieve the cpuset for a task */
   static inline struct cpuset *task_cs(struct task_struct *task)
   {
           return container_of(task_subsys_state(task, cpuset_subsys_id),
                               struct cpuset, css);
   }
   
   #ifdef CONFIG_NUMA
   static inline bool task_has_mempolicy(struct task_struct *task)
   {
           return task->mempolicy;
   }
   #else
   static inline bool task_has_mempolicy(struct task_struct *task)
   {
           return false;
   }
   #endif
   
   
   /* bits in struct cpuset flags field */
   typedef enum {
           CS_CPU_EXCLUSIVE,
           CS_MEM_EXCLUSIVE,
           CS_MEM_HARDWALL,
           CS_MEMORY_MIGRATE,
           CS_SCHED_LOAD_BALANCE,
           CS_SPREAD_PAGE,
           CS_SPREAD_SLAB,
   } cpuset_flagbits_t;
   
   /* the type of hotplug event */
   enum hotplug_event {
           CPUSET_CPU_OFFLINE,
           CPUSET_MEM_OFFLINE,
   };
   
   /* convenient tests for these bits */
   static inline int is_cpu_exclusive(const struct cpuset *cs)
   {
           return test_bit(CS_CPU_EXCLUSIVE, &cs->flags);
   }
   
   static inline int is_mem_exclusive(const struct cpuset *cs)
   {
           return test_bit(CS_MEM_EXCLUSIVE, &cs->flags);
   }
   
   static inline int is_mem_hardwall(const struct cpuset *cs)
   {
           return test_bit(CS_MEM_HARDWALL, &cs->flags);
   }
   
   static inline int is_sched_load_balance(const struct cpuset *cs)
   {
           return test_bit(CS_SCHED_LOAD_BALANCE, &cs->flags);
   }
   
   static inline int is_memory_migrate(const struct cpuset *cs)
   {
           return test_bit(CS_MEMORY_MIGRATE, &cs->flags);
   }
   
   static inline int is_spread_page(const struct cpuset *cs)
   {
           return test_bit(CS_SPREAD_PAGE, &cs->flags);
   }
   
   static inline int is_spread_slab(const struct cpuset *cs)
   {
           return test_bit(CS_SPREAD_SLAB, &cs->flags);
   }
   
   static struct cpuset top_cpuset = {
           .flags = ((1 << CS_CPU_EXCLUSIVE) | (1 << CS_MEM_EXCLUSIVE)),
   };
   
   /*
    * There are two global mutexes guarding cpuset structures.  The first
    * is the main control groups cgroup_mutex, accessed via
    * cgroup_lock()/cgroup_unlock().  The second is the cpuset-specific
    * callback_mutex, below. They can nest.  It is ok to first take
    * cgroup_mutex, then nest callback_mutex.  We also require taking
    * task_lock() when dereferencing a task's cpuset pointer.  See "The
    * task_lock() exception", at the end of this comment.
    *
    * A task must hold both mutexes to modify cpusets.  If a task
    * holds cgroup_mutex, then it blocks others wanting that mutex,
    * ensuring that it is the only task able to also acquire callback_mutex
    * and be able to modify cpusets.  It can perform various checks on
    * the cpuset structure first, knowing nothing will change.  It can
    * also allocate memory while just holding cgroup_mutex.  While it is
    * performing these checks, various callback routines can briefly
    * acquire callback_mutex to query cpusets.  Once it is ready to make
    * the changes, it takes callback_mutex, blocking everyone else.
    *
    * Calls to the kernel memory allocator can not be made while holding
    * callback_mutex, as that would risk double tripping on callback_mutex
    * from one of the callbacks into the cpuset code from within
    * __alloc_pages().
    *
    * If a task is only holding callback_mutex, then it has read-only
    * access to cpusets.
    *
    * Now, the task_struct fields mems_allowed and mempolicy may be changed
    * by other task, we use alloc_lock in the task_struct fields to protect
    * them.
    *
    * The cpuset_common_file_read() handlers only hold callback_mutex across
    * small pieces of code, such as when reading out possibly multi-word
    * cpumasks and nodemasks.
    *
    * Accessing a task's cpuset should be done in accordance with the
    * guidelines for accessing subsystem state in kernel/cgroup.c
    */
   
   static DEFINE_MUTEX(callback_mutex);
   
   /*
    * cpuset_buffer_lock protects both the cpuset_name and cpuset_nodelist
    * buffers.  They are statically allocated to prevent using excess stack
    * when calling cpuset_print_task_mems_allowed().
    */
   #define CPUSET_NAME_LEN         (128)
   #define CPUSET_NODELIST_LEN     (256)
   static char cpuset_name[CPUSET_NAME_LEN];
   static char cpuset_nodelist[CPUSET_NODELIST_LEN];
   static DEFINE_SPINLOCK(cpuset_buffer_lock);
   
   /*
    * This is ugly, but preserves the userspace API for existing cpuset
    * users. If someone tries to mount the "cpuset" filesystem, we
    * silently switch it to mount "cgroup" instead
    */
   static struct dentry *cpuset_mount(struct file_system_type *fs_type,
                            int flags, const char *unused_dev_name, void *data)
   {
           struct file_system_type *cgroup_fs = get_fs_type("cgroup");
           struct dentry *ret = ERR_PTR(-ENODEV);
           if (cgroup_fs) {
                   char mountopts[] =
                           "cpuset,noprefix,"
                           "release_agent=/sbin/cpuset_release_agent";
                   ret = cgroup_fs->mount(cgroup_fs, flags,
                                              unused_dev_name, mountopts);
                   put_filesystem(cgroup_fs);
           }
           return ret;
   }
   
   static struct file_system_type cpuset_fs_type = {
           .name = "cpuset",
           .mount = cpuset_mount,
   };
   
   /*
    * Return in pmask the portion of a cpusets's cpus_allowed that
    * are online.  If none are online, walk up the cpuset hierarchy
    * until we find one that does have some online cpus.  If we get
    * all the way to the top and still haven't found any online cpus,
    * return cpu_online_mask.  Or if passed a NULL cs from an exit'ing
    * task, return cpu_online_mask.
    *
    * One way or another, we guarantee to return some non-empty subset
    * of cpu_online_mask.
    *
    * Call with callback_mutex held.
    */
   
   static void guarantee_online_cpus(const struct cpuset *cs,
                                     struct cpumask *pmask)
   {
           while (cs && !cpumask_intersects(cs->cpus_allowed, cpu_online_mask))
                   cs = cs->parent;
           if (cs)
                   cpumask_and(pmask, cs->cpus_allowed, cpu_online_mask);
           else
                   cpumask_copy(pmask, cpu_online_mask);
           BUG_ON(!cpumask_intersects(pmask, cpu_online_mask));
   }
   
   /*
    * Return in *pmask the portion of a cpusets's mems_allowed that
    * are online, with memory.  If none are online with memory, walk
    * up the cpuset hierarchy until we find one that does have some
    * online mems.  If we get all the way to the top and still haven't
    * found any online mems, return node_states[N_MEMORY].
    *
    * One way or another, we guarantee to return some non-empty subset
    * of node_states[N_MEMORY].
    *
    * Call with callback_mutex held.
    */
   
   static void guarantee_online_mems(const struct cpuset *cs, nodemask_t *pmask)
   {
           while (cs && !nodes_intersects(cs->mems_allowed,
                                           node_states[N_MEMORY]))
                   cs = cs->parent;
           if (cs)
                   nodes_and(*pmask, cs->mems_allowed,
                                           node_states[N_MEMORY]);
           else
                   *pmask = node_states[N_MEMORY];
           BUG_ON(!nodes_intersects(*pmask, node_states[N_MEMORY]));
   }
   
   /*
    * update task's spread flag if cpuset's page/slab spread flag is set
    *
    * Called with callback_mutex/cgroup_mutex held
    */
   static void cpuset_update_task_spread_flag(struct cpuset *cs,
                                           struct task_struct *tsk)
   {
           if (is_spread_page(cs))
                   tsk->flags |= PF_SPREAD_PAGE;
           else
                   tsk->flags &= ~PF_SPREAD_PAGE;
           if (is_spread_slab(cs))
                   tsk->flags |= PF_SPREAD_SLAB;
           else
                   tsk->flags &= ~PF_SPREAD_SLAB;
   }
   
   /*
    * is_cpuset_subset(p, q) - Is cpuset p a subset of cpuset q?
    *
    * One cpuset is a subset of another if all its allowed CPUs and
    * Memory Nodes are a subset of the other, and its exclusive flags
    * are only set if the other's are set.  Call holding cgroup_mutex.
    */
   
   static int is_cpuset_subset(const struct cpuset *p, const struct cpuset *q)
   {
           return  cpumask_subset(p->cpus_allowed, q->cpus_allowed) &&
                   nodes_subset(p->mems_allowed, q->mems_allowed) &&
                   is_cpu_exclusive(p) <= is_cpu_exclusive(q) &&
                   is_mem_exclusive(p) <= is_mem_exclusive(q);
   }
   
   /**
    * alloc_trial_cpuset - allocate a trial cpuset
    * @cs: the cpuset that the trial cpuset duplicates
    */
   static struct cpuset *alloc_trial_cpuset(const struct cpuset *cs)
   {
           struct cpuset *trial;
   
           trial = kmemdup(cs, sizeof(*cs), GFP_KERNEL);
           if (!trial)
                   return NULL;
   
           if (!alloc_cpumask_var(&trial->cpus_allowed, GFP_KERNEL)) {
                   kfree(trial);
                   return NULL;
           }
           cpumask_copy(trial->cpus_allowed, cs->cpus_allowed);
   
           return trial;
   }
   
   /**
    * free_trial_cpuset - free the trial cpuset
    * @trial: the trial cpuset to be freed
    */
   static void free_trial_cpuset(struct cpuset *trial)
   {
           free_cpumask_var(trial->cpus_allowed);
           kfree(trial);
   }
   
   /*
    * validate_change() - Used to validate that any proposed cpuset change
    *                     follows the structural rules for cpusets.
    *
    * If we replaced the flag and mask values of the current cpuset
    * (cur) with those values in the trial cpuset (trial), would
    * our various subset and exclusive rules still be valid?  Presumes
    * cgroup_mutex held.
    *
    * 'cur' is the address of an actual, in-use cpuset.  Operations
    * such as list traversal that depend on the actual address of the
    * cpuset in the list must use cur below, not trial.
    *
    * 'trial' is the address of bulk structure copy of cur, with
    * perhaps one or more of the fields cpus_allowed, mems_allowed,
    * or flags changed to new, trial values.
    *
    * Return 0 if valid, -errno if not.
    */
   
   static int validate_change(const struct cpuset *cur, const struct cpuset *trial)
   {
           struct cgroup *cont;
           struct cpuset *c, *par;
   
           /* Each of our child cpusets must be a subset of us */
           list_for_each_entry(cont, &cur->css.cgroup->children, sibling) {
                   if (!is_cpuset_subset(cgroup_cs(cont), trial))
                           return -EBUSY;
           }
   
           /* Remaining checks don't apply to root cpuset */
           if (cur == &top_cpuset)
                   return 0;
   
           par = cur->parent;
   
           /* We must be a subset of our parent cpuset */
           if (!is_cpuset_subset(trial, par))
                   return -EACCES;
   
           /*
            * If either I or some sibling (!= me) is exclusive, we can't
            * overlap
            */
           list_for_each_entry(cont, &par->css.cgroup->children, sibling) {
                   c = cgroup_cs(cont);
                   if ((is_cpu_exclusive(trial) || is_cpu_exclusive(c)) &&
                       c != cur &&
                       cpumask_intersects(trial->cpus_allowed, c->cpus_allowed))
                           return -EINVAL;
                   if ((is_mem_exclusive(trial) || is_mem_exclusive(c)) &&
                       c != cur &&
                       nodes_intersects(trial->mems_allowed, c->mems_allowed))
                           return -EINVAL;
           }
   
           /* Cpusets with tasks can't have empty cpus_allowed or mems_allowed */
           if (cgroup_task_count(cur->css.cgroup)) {
                   if (cpumask_empty(trial->cpus_allowed) ||
                       nodes_empty(trial->mems_allowed)) {
                           return -ENOSPC;
                   }
           }
   
           return 0;
   }
   
   #ifdef CONFIG_SMP
   /*
    * Helper routine for generate_sched_domains().
    * Do cpusets a, b have overlapping cpus_allowed masks?
    */
   static int cpusets_overlap(struct cpuset *a, struct cpuset *b)
   {
           return cpumask_intersects(a->cpus_allowed, b->cpus_allowed);
   }
   
   static void
   update_domain_attr(struct sched_domain_attr *dattr, struct cpuset *c)
   {
           if (dattr->relax_domain_level < c->relax_domain_level)
                   dattr->relax_domain_level = c->relax_domain_level;
           return;
   }
   
   static void
   update_domain_attr_tree(struct sched_domain_attr *dattr, struct cpuset *c)
   {
           LIST_HEAD(q);
   
           list_add(&c->stack_list, &q);
           while (!list_empty(&q)) {
                   struct cpuset *cp;
                   struct cgroup *cont;
                   struct cpuset *child;
   
                   cp = list_first_entry(&q, struct cpuset, stack_list);
                   list_del(q.next);
   
                   if (cpumask_empty(cp->cpus_allowed))
                           continue;
   
                   if (is_sched_load_balance(cp))
                           update_domain_attr(dattr, cp);
   
                   list_for_each_entry(cont, &cp->css.cgroup->children, sibling) {
                           child = cgroup_cs(cont);
                           list_add_tail(&child->stack_list, &q);
                   }
           }
   }
   
   /*
    * generate_sched_domains()
    *
    * This function builds a partial partition of the systems CPUs
    * A 'partial partition' is a set of non-overlapping subsets whose
    * union is a subset of that set.
    * The output of this function needs to be passed to kernel/sched.c
    * partition_sched_domains() routine, which will rebuild the scheduler's
    * load balancing domains (sched domains) as specified by that partial
    * partition.
    *
    * See "What is sched_load_balance" in Documentation/cgroups/cpusets.txt
    * for a background explanation of this.
    *
    * Does not return errors, on the theory that the callers of this
    * routine would rather not worry about failures to rebuild sched
    * domains when operating in the severe memory shortage situations
    * that could cause allocation failures below.
    *
    * Must be called with cgroup_lock held.
    *
    * The three key local variables below are:
    *    q  - a linked-list queue of cpuset pointers, used to implement a
    *         top-down scan of all cpusets.  This scan loads a pointer
    *         to each cpuset marked is_sched_load_balance into the
    *         array 'csa'.  For our purposes, rebuilding the schedulers
    *         sched domains, we can ignore !is_sched_load_balance cpusets.
    *  csa  - (for CpuSet Array) Array of pointers to all the cpusets
    *         that need to be load balanced, for convenient iterative
    *         access by the subsequent code that finds the best partition,
    *         i.e the set of domains (subsets) of CPUs such that the
    *         cpus_allowed of every cpuset marked is_sched_load_balance
    *         is a subset of one of these domains, while there are as
    *         many such domains as possible, each as small as possible.
    * doms  - Conversion of 'csa' to an array of cpumasks, for passing to
    *         the kernel/sched.c routine partition_sched_domains() in a
    *         convenient format, that can be easily compared to the prior
    *         value to determine what partition elements (sched domains)
    *         were changed (added or removed.)
    *
    * Finding the best partition (set of domains):
    *      The triple nested loops below over i, j, k scan over the
    *      load balanced cpusets (using the array of cpuset pointers in
    *      csa[]) looking for pairs of cpusets that have overlapping
    *      cpus_allowed, but which don't have the same 'pn' partition
    *      number and gives them in the same partition number.  It keeps
    *      looping on the 'restart' label until it can no longer find
    *      any such pairs.
    *
    *      The union of the cpus_allowed masks from the set of
    *      all cpusets having the same 'pn' value then form the one
    *      element of the partition (one sched domain) to be passed to
    *      partition_sched_domains().
    */
   static int generate_sched_domains(cpumask_var_t **domains,
                           struct sched_domain_attr **attributes)
   {
           LIST_HEAD(q);           /* queue of cpusets to be scanned */
           struct cpuset *cp;      /* scans q */
           struct cpuset **csa;    /* array of all cpuset ptrs */
           int csn;                /* how many cpuset ptrs in csa so far */
           int i, j, k;            /* indices for partition finding loops */
           cpumask_var_t *doms;    /* resulting partition; i.e. sched domains */
           struct sched_domain_attr *dattr;  /* attributes for custom domains */
           int ndoms = 0;          /* number of sched domains in result */
           int nslot;              /* next empty doms[] struct cpumask slot */
   
           doms = NULL;
           dattr = NULL;
           csa = NULL;
   
           /* Special case for the 99% of systems with one, full, sched domain */
           if (is_sched_load_balance(&top_cpuset)) {
                   ndoms = 1;
                   doms = alloc_sched_domains(ndoms);
                   if (!doms)
                           goto done;
   
                   dattr = kmalloc(sizeof(struct sched_domain_attr), GFP_KERNEL);
                   if (dattr) {
                           *dattr = SD_ATTR_INIT;
                           update_domain_attr_tree(dattr, &top_cpuset);
                   }
                   cpumask_copy(doms[0], top_cpuset.cpus_allowed);
   
                   goto done;
           }
   
           csa = kmalloc(number_of_cpusets * sizeof(cp), GFP_KERNEL);
           if (!csa)
                   goto done;
           csn = 0;
   
           list_add(&top_cpuset.stack_list, &q);
           while (!list_empty(&q)) {
                   struct cgroup *cont;
                   struct cpuset *child;   /* scans child cpusets of cp */
   
                   cp = list_first_entry(&q, struct cpuset, stack_list);
                   list_del(q.next);
   
                   if (cpumask_empty(cp->cpus_allowed))
                           continue;
   
                   /*
                    * All child cpusets contain a subset of the parent's cpus, so
                    * just skip them, and then we call update_domain_attr_tree()
                    * to calc relax_domain_level of the corresponding sched
                    * domain.
                    */
                   if (is_sched_load_balance(cp)) {
                           csa[csn++] = cp;
                           continue;
                   }
   
                   list_for_each_entry(cont, &cp->css.cgroup->children, sibling) {
                           child = cgroup_cs(cont);
                           list_add_tail(&child->stack_list, &q);
                   }
           }
   
           for (i = 0; i < csn; i++)
                   csa[i]->pn = i;
           ndoms = csn;
   
   restart:
           /* Find the best partition (set of sched domains) */
           for (i = 0; i < csn; i++) {
                   struct cpuset *a = csa[i];
                   int apn = a->pn;
   
                   for (j = 0; j < csn; j++) {
                           struct cpuset *b = csa[j];
                           int bpn = b->pn;
   
                           if (apn != bpn && cpusets_overlap(a, b)) {
                                   for (k = 0; k < csn; k++) {
                                           struct cpuset *c = csa[k];
   
                                           if (c->pn == bpn)
                                                   c->pn = apn;
                                   }
                                   ndoms--;        /* one less element */
                                   goto restart;
                           }
                   }
           }
   
           /*
            * Now we know how many domains to create.
            * Convert <csn, csa> to <ndoms, doms> and populate cpu masks.
            */
           doms = alloc_sched_domains(ndoms);
           if (!doms)
                   goto done;
   
           /*
            * The rest of the code, including the scheduler, can deal with
            * dattr==NULL case. No need to abort if alloc fails.
            */
           dattr = kmalloc(ndoms * sizeof(struct sched_domain_attr), GFP_KERNEL);
   
           for (nslot = 0, i = 0; i < csn; i++) {
                   struct cpuset *a = csa[i];
                   struct cpumask *dp;
                   int apn = a->pn;
   
                   if (apn < 0) {
                           /* Skip completed partitions */
                           continue;
                   }
   
                   dp = doms[nslot];
   
                   if (nslot == ndoms) {
                           static int warnings = 10;
                           if (warnings) {
                                   printk(KERN_WARNING
                                    "rebuild_sched_domains confused:"
                                     " nslot %d, ndoms %d, csn %d, i %d,"
                                     " apn %d\n",
                                     nslot, ndoms, csn, i, apn);
                                   warnings--;
                           }
                           continue;
                   }
   
                   cpumask_clear(dp);
                   if (dattr)
                           *(dattr + nslot) = SD_ATTR_INIT;
                   for (j = i; j < csn; j++) {
                           struct cpuset *b = csa[j];
   
                           if (apn == b->pn) {
                                   cpumask_or(dp, dp, b->cpus_allowed);
                                   if (dattr)
                                           update_domain_attr_tree(dattr + nslot, b);
   
                                   /* Done with this partition */
                                   b->pn = -1;
                           }
                   }
                   nslot++;
           }
           BUG_ON(nslot != ndoms);
   
   done:
           kfree(csa);
   
           /*
            * Fallback to the default domain if kmalloc() failed.
            * See comments in partition_sched_domains().
            */
           if (doms == NULL)
                   ndoms = 1;
   
           *domains    = doms;
           *attributes = dattr;
           return ndoms;
   }
   
   /*
    * Rebuild scheduler domains.
    *
    * Call with neither cgroup_mutex held nor within get_online_cpus().
    * Takes both cgroup_mutex and get_online_cpus().
    *
    * Cannot be directly called from cpuset code handling changes
    * to the cpuset pseudo-filesystem, because it cannot be called
    * from code that already holds cgroup_mutex.
    */
   static void do_rebuild_sched_domains(struct work_struct *unused)
   {
           struct sched_domain_attr *attr;
           cpumask_var_t *doms;
           int ndoms;
   
           get_online_cpus();
   
           /* Generate domain masks and attrs */
           cgroup_lock();
           ndoms = generate_sched_domains(&doms, &attr);
           cgroup_unlock();
   
           /* Have scheduler rebuild the domains */
           partition_sched_domains(ndoms, doms, attr);
   
           put_online_cpus();
   }
   #else /* !CONFIG_SMP */
   static void do_rebuild_sched_domains(struct work_struct *unused)
   {
   }
   
   static int generate_sched_domains(cpumask_var_t **domains,
                           struct sched_domain_attr **attributes)
   {
           *domains = NULL;
           return 1;
   }
   #endif /* CONFIG_SMP */
   
   static DECLARE_WORK(rebuild_sched_domains_work, do_rebuild_sched_domains);
   
   /*
    * Rebuild scheduler domains, asynchronously via workqueue.
    *
    * If the flag 'sched_load_balance' of any cpuset with non-empty
    * 'cpus' changes, or if the 'cpus' allowed changes in any cpuset
    * which has that flag enabled, or if any cpuset with a non-empty
    * 'cpus' is removed, then call this routine to rebuild the
    * scheduler's dynamic sched domains.
    *
    * The rebuild_sched_domains() and partition_sched_domains()
    * routines must nest cgroup_lock() inside get_online_cpus(),
    * but such cpuset changes as these must nest that locking the
    * other way, holding cgroup_lock() for much of the code.
    *
    * So in order to avoid an ABBA deadlock, the cpuset code handling
    * these user changes delegates the actual sched domain rebuilding
    * to a separate workqueue thread, which ends up processing the
    * above do_rebuild_sched_domains() function.
    */
   static void async_rebuild_sched_domains(void)
   {
           queue_work(cpuset_wq, &rebuild_sched_domains_work);
   }
   
   /*
    * Accomplishes the same scheduler domain rebuild as the above
    * async_rebuild_sched_domains(), however it directly calls the
    * rebuild routine synchronously rather than calling it via an
    * asynchronous work thread.
    *
    * This can only be called from code that is not holding
    * cgroup_mutex (not nested in a cgroup_lock() call.)
    */
   void rebuild_sched_domains(void)
   {
           do_rebuild_sched_domains(NULL);
   }
   
   /**
    * cpuset_test_cpumask - test a task's cpus_allowed versus its cpuset's
    * @tsk: task to test
    * @scan: struct cgroup_scanner contained in its struct cpuset_hotplug_scanner
    *
    * Call with cgroup_mutex held.  May take callback_mutex during call.
    * Called for each task in a cgroup by cgroup_scan_tasks().
    * Return nonzero if this tasks's cpus_allowed mask should be changed (in other
    * words, if its mask is not equal to its cpuset's mask).
    */
   static int cpuset_test_cpumask(struct task_struct *tsk,
                                  struct cgroup_scanner *scan)
   {
           return !cpumask_equal(&tsk->cpus_allowed,
                           (cgroup_cs(scan->cg))->cpus_allowed);
   }
   
   /**
    * cpuset_change_cpumask - make a task's cpus_allowed the same as its cpuset's
    * @tsk: task to test
    * @scan: struct cgroup_scanner containing the cgroup of the task
    *
    * Called by cgroup_scan_tasks() for each task in a cgroup whose
    * cpus_allowed mask needs to be changed.
    *
    * We don't need to re-check for the cgroup/cpuset membership, since we're
    * holding cgroup_lock() at this point.
    */
   static void cpuset_change_cpumask(struct task_struct *tsk,
                                     struct cgroup_scanner *scan)
   {
           set_cpus_allowed_ptr(tsk, ((cgroup_cs(scan->cg))->cpus_allowed));
   }
   
   /**
    * update_tasks_cpumask - Update the cpumasks of tasks in the cpuset.
    * @cs: the cpuset in which each task's cpus_allowed mask needs to be changed
    * @heap: if NULL, defer allocating heap memory to cgroup_scan_tasks()
    *
    * Called with cgroup_mutex held
    *
    * The cgroup_scan_tasks() function will scan all the tasks in a cgroup,
    * calling callback functions for each.
    *
    * No return value. It's guaranteed that cgroup_scan_tasks() always returns 0
    * if @heap != NULL.
    */
   static void update_tasks_cpumask(struct cpuset *cs, struct ptr_heap *heap)
   {
           struct cgroup_scanner scan;
   
           scan.cg = cs->css.cgroup;
           scan.test_task = cpuset_test_cpumask;
           scan.process_task = cpuset_change_cpumask;
           scan.heap = heap;
           cgroup_scan_tasks(&scan);
   }
   
   /**
    * update_cpumask - update the cpus_allowed mask of a cpuset and all tasks in it
    * @cs: the cpuset to consider
    * @buf: buffer of cpu numbers written to this cpuset
    */
   static int update_cpumask(struct cpuset *cs, struct cpuset *trialcs,
                             const char *buf)
   {
           struct ptr_heap heap;
           int retval;
           int is_load_balanced;
   
           /* top_cpuset.cpus_allowed tracks cpu_online_mask; it's read-only */
           if (cs == &top_cpuset)
                   return -EACCES;
   
           /*
            * An empty cpus_allowed is ok only if the cpuset has no tasks.
            * Since cpulist_parse() fails on an empty mask, we special case
            * that parsing.  The validate_change() call ensures that cpusets
            * with tasks have cpus.
            */
           if (!*buf) {
                   cpumask_clear(trialcs->cpus_allowed);
           } else {
                   retval = cpulist_parse(buf, trialcs->cpus_allowed);
                   if (retval < 0)
                           return retval;
   
                   if (!cpumask_subset(trialcs->cpus_allowed, cpu_active_mask))
                           return -EINVAL;
           }
           retval = validate_change(cs, trialcs);
           if (retval < 0)
                   return retval;
   
           /* Nothing to do if the cpus didn't change */
           if (cpumask_equal(cs->cpus_allowed, trialcs->cpus_allowed))
                   return 0;
   
           retval = heap_init(&heap, PAGE_SIZE, GFP_KERNEL, NULL);
           if (retval)
                   return retval;
   
           is_load_balanced = is_sched_load_balance(trialcs);
   
           mutex_lock(&callback_mutex);
           cpumask_copy(cs->cpus_allowed, trialcs->cpus_allowed);
           mutex_unlock(&callback_mutex);
   
           /*
            * Scan tasks in the cpuset, and update the cpumasks of any
            * that need an update.
            */
           update_tasks_cpumask(cs, &heap);
   
           heap_free(&heap);
   
           if (is_load_balanced)
                   async_rebuild_sched_domains();
           return 0;
   }
   
   /*
    * cpuset_migrate_mm
    *
    *    Migrate memory region from one set of nodes to another.
    *
    *    Temporarilly set tasks mems_allowed to target nodes of migration,
    *    so that the migration code can allocate pages on these nodes.
    *
    *    Call holding cgroup_mutex, so current's cpuset won't change
    *    during this call, as manage_mutex holds off any cpuset_attach()
    *    calls.  Therefore we don't need to take task_lock around the
    *    call to guarantee_online_mems(), as we know no one is changing
    *    our task's cpuset.
    *
    *    While the mm_struct we are migrating is typically from some
    *    other task, the task_struct mems_allowed that we are hacking
    *    is for our current task, which must allocate new pages for that
    *    migrating memory region.
    */
   
   static void cpuset_migrate_mm(struct mm_struct *mm, const nodemask_t *from,
                                                           const nodemask_t *to)
   {
           struct task_struct *tsk = current;
   
           tsk->mems_allowed = *to;
   
           do_migrate_pages(mm, from, to, MPOL_MF_MOVE_ALL);
   
           guarantee_online_mems(task_cs(tsk),&tsk->mems_allowed);
   }
   
   /*
    * cpuset_change_task_nodemask - change task's mems_allowed and mempolicy
    * @tsk: the task to change
    * @newmems: new nodes that the task will be set
    *
    * In order to avoid seeing no nodes if the old and new nodes are disjoint,
    * we structure updates as setting all new allowed nodes, then clearing newly
    * disallowed ones.
    */
   static void cpuset_change_task_nodemask(struct task_struct *tsk,
                                           nodemask_t *newmems)
   {
           bool need_loop;
   
           /*
            * Allow tasks that have access to memory reserves because they have
            * been OOM killed to get memory anywhere.
            */
           if (unlikely(test_thread_flag(TIF_MEMDIE)))
                   return;
           if (current->flags & PF_EXITING) /* Let dying task have memory */
                   return;
   
           task_lock(tsk);
           /*
            * Determine if a loop is necessary if another thread is doing
            * get_mems_allowed().  If at least one node remains unchanged and
            * tsk does not have a mempolicy, then an empty nodemask will not be
            * possible when mems_allowed is larger than a word.
            */
           need_loop = task_has_mempolicy(tsk) ||
                           !nodes_intersects(*newmems, tsk->mems_allowed);
   
           if (need_loop)
                   write_seqcount_begin(&tsk->mems_allowed_seq);
   
           nodes_or(tsk->mems_allowed, tsk->mems_allowed, *newmems);
           mpol_rebind_task(tsk, newmems, MPOL_REBIND_STEP1);
   
           mpol_rebind_task(tsk, newmems, MPOL_REBIND_STEP2);
           tsk->mems_allowed = *newmems;
  
          if (need_loop)
                  write_seqcount_end(&tsk->mems_allowed_seq);
  
          task_unlock(tsk);
  }
  
  /*
   * Update task's mems_allowed and rebind its mempolicy and vmas' mempolicy
   * of it to cpuset's new mems_allowed, and migrate pages to new nodes if
   * memory_migrate flag is set. Called with cgroup_mutex held.
   */
  static void cpuset_change_nodemask(struct task_struct *p,
                                     struct cgroup_scanner *scan)
  {
          struct mm_struct *mm;
          struct cpuset *cs;
          int migrate;
          const nodemask_t *oldmem = scan->data;
          static nodemask_t newmems;      /* protected by cgroup_mutex */
  
          cs = cgroup_cs(scan->cg);
          guarantee_online_mems(cs, &newmems);
  
          cpuset_change_task_nodemask(p, &newmems);
  
          mm = get_task_mm(p);
          if (!mm)
                  return;
  
          migrate = is_memory_migrate(cs);
  
          mpol_rebind_mm(mm, &cs->mems_allowed);
          if (migrate)
                  cpuset_migrate_mm(mm, oldmem, &cs->mems_allowed);
          mmput(mm);
  }
  
  static void *cpuset_being_rebound;
  
  /**
   * update_tasks_nodemask - Update the nodemasks of tasks in the cpuset.
   * @cs: the cpuset in which each task's mems_allowed mask needs to be changed
   * @oldmem: old mems_allowed of cpuset cs
   * @heap: if NULL, defer allocating heap memory to cgroup_scan_tasks()
   *
   * Called with cgroup_mutex held
   * No return value. It's guaranteed that cgroup_scan_tasks() always returns 0
   * if @heap != NULL.
   */
  static void update_tasks_nodemask(struct cpuset *cs, const nodemask_t *oldmem,
                                   struct ptr_heap *heap)
  {
          struct cgroup_scanner scan;
  
          cpuset_being_rebound = cs;              /* causes mpol_dup() rebind */
  
          scan.cg = cs->css.cgroup;
          scan.test_task = NULL;
          scan.process_task = cpuset_change_nodemask;
          scan.heap = heap;
          scan.data = (nodemask_t *)oldmem;
  
          /*
           * The mpol_rebind_mm() call takes mmap_sem, which we couldn't
           * take while holding tasklist_lock.  Forks can happen - the
           * mpol_dup() cpuset_being_rebound check will catch such forks,
           * and rebind their vma mempolicies too.  Because we still hold
           * the global cgroup_mutex, we know that no other rebind effort
           * will be contending for the global variable cpuset_being_rebound.
           * It's ok if we rebind the same mm twice; mpol_rebind_mm()
           * is idempotent.  Also migrate pages in each mm to new nodes.
           */
          cgroup_scan_tasks(&scan);
  
          /* We're done rebinding vmas to this cpuset's new mems_allowed. */
          cpuset_being_rebound = NULL;
  }
  
  /*
   * Handle user request to change the 'mems' memory placement
   * of a cpuset.  Needs to validate the request, update the
   * cpusets mems_allowed, and for each task in the cpuset,
   * update mems_allowed and rebind task's mempolicy and any vma
   * mempolicies and if the cpuset is marked 'memory_migrate',
   * migrate the tasks pages to the new memory.
   *
   * Call with cgroup_mutex held.  May take callback_mutex during call.
   * Will take tasklist_lock, scan tasklist for tasks in cpuset cs,
   * lock each such tasks mm->mmap_sem, scan its vma's and rebind
   * their mempolicies to the cpusets new mems_allowed.
   */
  static int update_nodemask(struct cpuset *cs, struct cpuset *trialcs,
                             const char *buf)
  {
          NODEMASK_ALLOC(nodemask_t, oldmem, GFP_KERNEL);
          int retval;
          struct ptr_heap heap;
  
          if (!oldmem)
                  return -ENOMEM;
  
          /*
           * top_cpuset.mems_allowed tracks node_stats[N_MEMORY];
           * it's read-only
           */
          if (cs == &top_cpuset) {
                  retval = -EACCES;
                  goto done;
          }
  
          /*
           * An empty mems_allowed is ok iff there are no tasks in the cpuset.
           * Since nodelist_parse() fails on an empty mask, we special case
           * that parsing.  The validate_change() call ensures that cpusets
           * with tasks have memory.
           */
          if (!*buf) {
                  nodes_clear(trialcs->mems_allowed);
          } else {
                  retval = nodelist_parse(buf, trialcs->mems_allowed);
                  if (retval < 0)
                          goto done;
  
                  if (!nodes_subset(trialcs->mems_allowed,
                                  node_states[N_MEMORY])) {
                          retval =  -EINVAL;
                          goto done;
                  }
          }
          *oldmem = cs->mems_allowed;
          if (nodes_equal(*oldmem, trialcs->mems_allowed)) {
                  retval = 0;             /* Too easy - nothing to do */
                  goto done;
          }
          retval = validate_change(cs, trialcs);
          if (retval < 0)
                  goto done;
  
          retval = heap_init(&heap, PAGE_SIZE, GFP_KERNEL, NULL);
          if (retval < 0)
                  goto done;
  
          mutex_lock(&callback_mutex);
          cs->mems_allowed = trialcs->mems_allowed;
          mutex_unlock(&callback_mutex);
  
          update_tasks_nodemask(cs, oldmem, &heap);
  
          heap_free(&heap);
  done:
          NODEMASK_FREE(oldmem);
          return retval;
  }
  
  int current_cpuset_is_being_rebound(void)
  {
          return task_cs(current) == cpuset_being_rebound;
  }
  
  static int update_relax_domain_level(struct cpuset *cs, s64 val)
  {
  #ifdef CONFIG_SMP
          if (val < -1 || val >= sched_domain_level_max)
                  return -EINVAL;
  #endif
  
          if (val != cs->relax_domain_level) {
                  cs->relax_domain_level = val;
                  if (!cpumask_empty(cs->cpus_allowed) &&
                      is_sched_load_balance(cs))
                          async_rebuild_sched_domains();
          }
  
          return 0;
  }
  
  /*
   * cpuset_change_flag - make a task's spread flags the same as its cpuset's
   * @tsk: task to be updated
   * @scan: struct cgroup_scanner containing the cgroup of the task
   *
   * Called by cgroup_scan_tasks() for each task in a cgroup.
   *
   * We don't need to re-check for the cgroup/cpuset membership, since we're
   * holding cgroup_lock() at this point.
   */
  static void cpuset_change_flag(struct task_struct *tsk,
                                  struct cgroup_scanner *scan)
  {
          cpuset_update_task_spread_flag(cgroup_cs(scan->cg), tsk);
  }
  
  /*
   * update_tasks_flags - update the spread flags of tasks in the cpuset.
   * @cs: the cpuset in which each task's spread flags needs to be changed
   * @heap: if NULL, defer allocating heap memory to cgroup_scan_tasks()
   *
   * Called with cgroup_mutex held
   *
   * The cgroup_scan_tasks() function will scan all the tasks in a cgroup,
   * calling callback functions for each.
   *
   * No return value. It's guaranteed that cgroup_scan_tasks() always returns 0
   * if @heap != NULL.
   */
  static void update_tasks_flags(struct cpuset *cs, struct ptr_heap *heap)
  {
          struct cgroup_scanner scan;
  
          scan.cg = cs->css.cgroup;
          scan.test_task = NULL;
          scan.process_task = cpuset_change_flag;
          scan.heap = heap;
          cgroup_scan_tasks(&scan);
  }
  
  /*
   * update_flag - read a 0 or a 1 in a file and update associated flag
   * bit:         the bit to update (see cpuset_flagbits_t)
   * cs:          the cpuset to update
   * turning_on:  whether the flag is being set or cleared
   *
   * Call with cgroup_mutex held.
   */
  
  static int update_flag(cpuset_flagbits_t bit, struct cpuset *cs,
                         int turning_on)
  {
          struct cpuset *trialcs;
          int balance_flag_changed;
          int spread_flag_changed;
          struct ptr_heap heap;
          int err;
  
          trialcs = alloc_trial_cpuset(cs);
          if (!trialcs)
                  return -ENOMEM;
  
          if (turning_on)
                  set_bit(bit, &trialcs->flags);
          else
                  clear_bit(bit, &trialcs->flags);
  
          err = validate_change(cs, trialcs);
          if (err < 0)
                  goto out;
  
          err = heap_init(&heap, PAGE_SIZE, GFP_KERNEL, NULL);
          if (err < 0)
                  goto out;
  
          balance_flag_changed = (is_sched_load_balance(cs) !=
                                  is_sched_load_balance(trialcs));
  
          spread_flag_changed = ((is_spread_slab(cs) != is_spread_slab(trialcs))
                          || (is_spread_page(cs) != is_spread_page(trialcs)));
  
          mutex_lock(&callback_mutex);
          cs->flags = trialcs->flags;
          mutex_unlock(&callback_mutex);
  
          if (!cpumask_empty(trialcs->cpus_allowed) && balance_flag_changed)
                  async_rebuild_sched_domains();
  
          if (spread_flag_changed)
                  update_tasks_flags(cs, &heap);
          heap_free(&heap);
  out:
          free_trial_cpuset(trialcs);
          return err;
  }
  
  /*
   * Frequency meter - How fast is some event occurring?
   *
   * These routines manage a digitally filtered, constant time based,
   * event frequency meter.  There are four routines:
   *   fmeter_init() - initialize a frequency meter.
   *   fmeter_markevent() - called each time the event happens.
   *   fmeter_getrate() - returns the recent rate of such events.
   *   fmeter_update() - internal routine used to update fmeter.
   *
   * A common data structure is passed to each of these routines,
   * which is used to keep track of the state required to manage the
   * frequency meter and its digital filter.
   *
   * The filter works on the number of events marked per unit time.
   * The filter is single-pole low-pass recursive (IIR).  The time unit
   * is 1 second.  Arithmetic is done using 32-bit integers scaled to
   * simulate 3 decimal digits of precision (multiplied by 1000).
   *
   * With an FM_COEF of 933, and a time base of 1 second, the filter
   * has a half-life of 10 seconds, meaning that if the events quit
   * happening, then the rate returned from the fmeter_getrate()
   * will be cut in half each 10 seconds, until it converges to zero.
   *
   * It is not worth doing a real infinitely recursive filter.  If more
   * than FM_MAXTICKS ticks have elapsed since the last filter event,
   * just compute FM_MAXTICKS ticks worth, by which point the level
   * will be stable.
   *
   * Limit the count of unprocessed events to FM_MAXCNT, so as to avoid
   * arithmetic overflow in the fmeter_update() routine.
   *
   * Given the simple 32 bit integer arithmetic used, this meter works
   * best for reporting rates between one per millisecond (msec) and
   * one per 32 (approx) seconds.  At constant rates faster than one
   * per msec it maxes out at values just under 1,000,000.  At constant
   * rates between one per msec, and one per second it will stabilize
   * to a value N*1000, where N is the rate of events per second.
   * At constant rates between one per second and one per 32 seconds,
   * it will be choppy, moving up on the seconds that have an event,
   * and then decaying until the next event.  At rates slower than
   * about one in 32 seconds, it decays all the way back to zero between
   * each event.
   */
  
  #define FM_COEF 933             /* coefficient for half-life of 10 secs */
  #define FM_MAXTICKS ((time_t)99) /* useless computing more ticks than this */
  #define FM_MAXCNT 1000000       /* limit cnt to avoid overflow */
  #define FM_SCALE 1000           /* faux fixed point scale */
  
  /* Initialize a frequency meter */
  static void fmeter_init(struct fmeter *fmp)
  {
          fmp->cnt = 0;
          fmp->val = 0;
          fmp->time = 0;
          spin_lock_init(&fmp->lock);
  }
  
  /* Internal meter update - process cnt events and update value */
  static void fmeter_update(struct fmeter *fmp)
  {
          time_t now = get_seconds();
          time_t ticks = now - fmp->time;
  
          if (ticks == 0)
                  return;
  
          ticks = min(FM_MAXTICKS, ticks);
          while (ticks-- > 0)
                  fmp->val = (FM_COEF * fmp->val) / FM_SCALE;
          fmp->time = now;
  
          fmp->val += ((FM_SCALE - FM_COEF) * fmp->cnt) / FM_SCALE;
          fmp->cnt = 0;
  }
  
  /* Process any previous ticks, then bump cnt by one (times scale). */
  static void fmeter_markevent(struct fmeter *fmp)
  {
          spin_lock(&fmp->lock);
          fmeter_update(fmp);
          fmp->cnt = min(FM_MAXCNT, fmp->cnt + FM_SCALE);
          spin_unlock(&fmp->lock);
  }
  
  /* Process any previous ticks, then return current value. */
  static int fmeter_getrate(struct fmeter *fmp)
  {
          int val;
  
          spin_lock(&fmp->lock);
          fmeter_update(fmp);
          val = fmp->val;
          spin_unlock(&fmp->lock);
          return val;
  }
  
  /*
   * Protected by cgroup_lock. The nodemasks must be stored globally because
   * dynamically allocating them is not allowed in can_attach, and they must
   * persist until attach.
   */
  static cpumask_var_t cpus_attach;
  static nodemask_t cpuset_attach_nodemask_from;
  static nodemask_t cpuset_attach_nodemask_to;
  
  /* Called by cgroups to determine if a cpuset is usable; cgroup_mutex held */
  static int cpuset_can_attach(struct cgroup *cgrp, struct cgroup_taskset *tset)
  {
          struct cpuset *cs = cgroup_cs(cgrp);
          struct task_struct *task;
          int ret;
  
          if (cpumask_empty(cs->cpus_allowed) || nodes_empty(cs->mems_allowed))
                  return -ENOSPC;
  
          cgroup_taskset_for_each(task, cgrp, tset) {
                  /*
                   * Kthreads bound to specific cpus cannot be moved to a new
                   * cpuset; we cannot change their cpu affinity and
                   * isolating such threads by their set of allowed nodes is
                   * unnecessary.  Thus, cpusets are not applicable for such
                   * threads.  This prevents checking for success of
                   * set_cpus_allowed_ptr() on all attached tasks before
                   * cpus_allowed may be changed.
                   */
                  if (task->flags & PF_THREAD_BOUND)
                          return -EINVAL;
                  if ((ret = security_task_setscheduler(task)))
                          return ret;
          }
  
          /* prepare for attach */
          if (cs == &top_cpuset)
                  cpumask_copy(cpus_attach, cpu_possible_mask);
          else
                  guarantee_online_cpus(cs, cpus_attach);
  
          guarantee_online_mems(cs, &cpuset_attach_nodemask_to);
  
          return 0;
  }
  
  static void cpuset_attach(struct cgroup *cgrp, struct cgroup_taskset *tset)
  {
          struct mm_struct *mm;
          struct task_struct *task;
          struct task_struct *leader = cgroup_taskset_first(tset);
          struct cgroup *oldcgrp = cgroup_taskset_cur_cgroup(tset);
          struct cpuset *cs = cgroup_cs(cgrp);
          struct cpuset *oldcs = cgroup_cs(oldcgrp);
  
          cgroup_taskset_for_each(task, cgrp, tset) {
                  /*
                   * can_attach beforehand should guarantee that this doesn't
                   * fail.  TODO: have a better way to handle failure here
                   */
                  WARN_ON_ONCE(set_cpus_allowed_ptr(task, cpus_attach));
  
                  cpuset_change_task_nodemask(task, &cpuset_attach_nodemask_to);
                  cpuset_update_task_spread_flag(cs, task);
          }
  
          /*
           * Change mm, possibly for multiple threads in a threadgroup. This is
           * expensive and may sleep.
           */
          cpuset_attach_nodemask_from = oldcs->mems_allowed;
          cpuset_attach_nodemask_to = cs->mems_allowed;
          mm = get_task_mm(leader);
          if (mm) {
                  mpol_rebind_mm(mm, &cpuset_attach_nodemask_to);
                  if (is_memory_migrate(cs))
                          cpuset_migrate_mm(mm, &cpuset_attach_nodemask_from,
                                            &cpuset_attach_nodemask_to);
                  mmput(mm);
          }
  }
  
  /* The various types of files and directories in a cpuset file system */
  
  typedef enum {
          FILE_MEMORY_MIGRATE,
          FILE_CPULIST,
          FILE_MEMLIST,
          FILE_CPU_EXCLUSIVE,
          FILE_MEM_EXCLUSIVE,
          FILE_MEM_HARDWALL,
          FILE_SCHED_LOAD_BALANCE,
          FILE_SCHED_RELAX_DOMAIN_LEVEL,
          FILE_MEMORY_PRESSURE_ENABLED,
          FILE_MEMORY_PRESSURE,
          FILE_SPREAD_PAGE,
          FILE_SPREAD_SLAB,
  } cpuset_filetype_t;
  
  static int cpuset_write_u64(struct cgroup *cgrp, struct cftype *cft, u64 val)
  {
          int retval = 0;
          struct cpuset *cs = cgroup_cs(cgrp);
          cpuset_filetype_t type = cft->private;
  
          if (!cgroup_lock_live_group(cgrp))
                  return -ENODEV;
  
          switch (type) {
          case FILE_CPU_EXCLUSIVE:
                  retval = update_flag(CS_CPU_EXCLUSIVE, cs, val);
                  break;
          case FILE_MEM_EXCLUSIVE:
                  retval = update_flag(CS_MEM_EXCLUSIVE, cs, val);
                  break;
          case FILE_MEM_HARDWALL:
                  retval = update_flag(CS_MEM_HARDWALL, cs, val);
                  break;
          case FILE_SCHED_LOAD_BALANCE:
                  retval = update_flag(CS_SCHED_LOAD_BALANCE, cs, val);
                  break;
          case FILE_MEMORY_MIGRATE:
                  retval = update_flag(CS_MEMORY_MIGRATE, cs, val);
                  break;
          case FILE_MEMORY_PRESSURE_ENABLED:
                  cpuset_memory_pressure_enabled = !!val;
                  break;
          case FILE_MEMORY_PRESSURE:
                  retval = -EACCES;
                  break;
          case FILE_SPREAD_PAGE:
                  retval = update_flag(CS_SPREAD_PAGE, cs, val);
                  break;
          case FILE_SPREAD_SLAB:
                  retval = update_flag(CS_SPREAD_SLAB, cs, val);
                  break;
          default:
                  retval = -EINVAL;
                  break;
          }
          cgroup_unlock();
          return retval;
  }
  
  static int cpuset_write_s64(struct cgroup *cgrp, struct cftype *cft, s64 val)
  {
          int retval = 0;
          struct cpuset *cs = cgroup_cs(cgrp);
          cpuset_filetype_t type = cft->private;
  
          if (!cgroup_lock_live_group(cgrp))
                  return -ENODEV;
  
          switch (type) {
          case FILE_SCHED_RELAX_DOMAIN_LEVEL:
                  retval = update_relax_domain_level(cs, val);
                  break;
          default:
                  retval = -EINVAL;
                  break;
          }
          cgroup_unlock();
          return retval;
  }
  
  /*
   * Common handling for a write to a "cpus" or "mems" file.
   */
  static int cpuset_write_resmask(struct cgroup *cgrp, struct cftype *cft,
                                  const char *buf)
  {
          int retval = 0;
          struct cpuset *cs = cgroup_cs(cgrp);
          struct cpuset *trialcs;
  
          if (!cgroup_lock_live_group(cgrp))
                  return -ENODEV;
  
          trialcs = alloc_trial_cpuset(cs);
          if (!trialcs) {
                  retval = -ENOMEM;
                  goto out;
          }
  
          switch (cft->private) {
          case FILE_CPULIST:
                  retval = update_cpumask(cs, trialcs, buf);
                  break;
          case FILE_MEMLIST:
                  retval = update_nodemask(cs, trialcs, buf);
                  break;
          default:
                  retval = -EINVAL;
                  break;
          }
  
          free_trial_cpuset(trialcs);
  out:
          cgroup_unlock();
          return retval;
  }
  
  /*
   * These ascii lists should be read in a single call, by using a user
   * buffer large enough to hold the entire map.  If read in smaller
   * chunks, there is no guarantee of atomicity.  Since the display format
   * used, list of ranges of sequential numbers, is variable length,
   * and since these maps can change value dynamically, one could read
   * gibberish by doing partial reads while a list was changing.
   * A single large read to a buffer that crosses a page boundary is
   * ok, because the result being copied to user land is not recomputed
   * across a page fault.
   */
  
  static size_t cpuset_sprintf_cpulist(char *page, struct cpuset *cs)
  {
          size_t count;
  
          mutex_lock(&callback_mutex);
          count = cpulist_scnprintf(page, PAGE_SIZE, cs->cpus_allowed);
          mutex_unlock(&callback_mutex);
  
          return count;
  }
  
  static size_t cpuset_sprintf_memlist(char *page, struct cpuset *cs)
  {
          size_t count;
  
          mutex_lock(&callback_mutex);
          count = nodelist_scnprintf(page, PAGE_SIZE, cs->mems_allowed);
          mutex_unlock(&callback_mutex);
  
          return count;
  }
  
  static ssize_t cpuset_common_file_read(struct cgroup *cont,
                                         struct cftype *cft,
                                         struct file *file,
                                         char __user *buf,
                                         size_t nbytes, loff_t *ppos)
  {
          struct cpuset *cs = cgroup_cs(cont);
          cpuset_filetype_t type = cft->private;
          char *page;
          ssize_t retval = 0;
          char *s;
  
          if (!(page = (char *)__get_free_page(GFP_TEMPORARY)))
                  return -ENOMEM;
  
          s = page;
  
          switch (type) {
          case FILE_CPULIST:
                  s += cpuset_sprintf_cpulist(s, cs);
                  break;
          case FILE_MEMLIST:
                  s += cpuset_sprintf_memlist(s, cs);
                  break;
          default:
                  retval = -EINVAL;
                  goto out;
          }
          *s++ = '\n';
  
          retval = simple_read_from_buffer(buf, nbytes, ppos, page, s - page);
  out:
          free_page((unsigned long)page);
          return retval;
  }
  
  static u64 cpuset_read_u64(struct cgroup *cont, struct cftype *cft)
  {
          struct cpuset *cs = cgroup_cs(cont);
          cpuset_filetype_t type = cft->private;
          switch (type) {
          case FILE_CPU_EXCLUSIVE:
                  return is_cpu_exclusive(cs);
          case FILE_MEM_EXCLUSIVE:
                  return is_mem_exclusive(cs);
          case FILE_MEM_HARDWALL:
                  return is_mem_hardwall(cs);
          case FILE_SCHED_LOAD_BALANCE:
                  return is_sched_load_balance(cs);
          case FILE_MEMORY_MIGRATE:
                  return is_memory_migrate(cs);
          case FILE_MEMORY_PRESSURE_ENABLED:
                  return cpuset_memory_pressure_enabled;
          case FILE_MEMORY_PRESSURE:
                  return fmeter_getrate(&cs->fmeter);
          case FILE_SPREAD_PAGE:
                  return is_spread_page(cs);
          case FILE_SPREAD_SLAB:
                  return is_spread_slab(cs);
          default:
                  BUG();
          }
  
          /* Unreachable but makes gcc happy */
          return 0;
  }
  
  static s64 cpuset_read_s64(struct cgroup *cont, struct cftype *cft)
  {
          struct cpuset *cs = cgroup_cs(cont);
          cpuset_filetype_t type = cft->private;
          switch (type) {
          case FILE_SCHED_RELAX_DOMAIN_LEVEL:
                  return cs->relax_domain_level;
          default:
                  BUG();
          }
  
          /* Unrechable but makes gcc happy */
          return 0;
  }
  
  
  /*
   * for the common functions, 'private' gives the type of file
   */
  
  static struct cftype files[] = {
          {
                  .name = "cpus",
                  .read = cpuset_common_file_read,
                  .write_string = cpuset_write_resmask,
                  .max_write_len = (100U + 6 * NR_CPUS),
                  .private = FILE_CPULIST,
          },
  
          {
                  .name = "mems",
                  .read = cpuset_common_file_read,
                  .write_string = cpuset_write_resmask,
                  .max_write_len = (100U + 6 * MAX_NUMNODES),
                  .private = FILE_MEMLIST,
          },
  
          {
                  .name = "cpu_exclusive",
                  .read_u64 = cpuset_read_u64,
                  .write_u64 = cpuset_write_u64,
                  .private = FILE_CPU_EXCLUSIVE,
          },
  
          {
                  .name = "mem_exclusive",
                  .read_u64 = cpuset_read_u64,
                  .write_u64 = cpuset_write_u64,
                  .private = FILE_MEM_EXCLUSIVE,
          },
  
          {
                  .name = "mem_hardwall",
                  .read_u64 = cpuset_read_u64,
                  .write_u64 = cpuset_write_u64,
                  .private = FILE_MEM_HARDWALL,
          },
  
          {
                  .name = "sched_load_balance",
                  .read_u64 = cpuset_read_u64,
                  .write_u64 = cpuset_write_u64,
                  .private = FILE_SCHED_LOAD_BALANCE,
          },
  
          {
                  .name = "sched_relax_domain_level",
                  .read_s64 = cpuset_read_s64,
                  .write_s64 = cpuset_write_s64,
                  .private = FILE_SCHED_RELAX_DOMAIN_LEVEL,
          },
  
          {
                  .name = "memory_migrate",
                  .read_u64 = cpuset_read_u64,
                  .write_u64 = cpuset_write_u64,
                  .private = FILE_MEMORY_MIGRATE,
          },
  
          {
                  .name = "memory_pressure",
                  .read_u64 = cpuset_read_u64,
                  .write_u64 = cpuset_write_u64,
                  .private = FILE_MEMORY_PRESSURE,
                  .mode = S_IRUGO,
          },
  
          {
                  .name = "memory_spread_page",
                  .read_u64 = cpuset_read_u64,
                  .write_u64 = cpuset_write_u64,
                  .private = FILE_SPREAD_PAGE,
          },
  
          {
                  .name = "memory_spread_slab",
                  .read_u64 = cpuset_read_u64,
                  .write_u64 = cpuset_write_u64,
                  .private = FILE_SPREAD_SLAB,
          },
  
          {
                  .name = "memory_pressure_enabled",
                  .flags = CFTYPE_ONLY_ON_ROOT,
                  .read_u64 = cpuset_read_u64,
                  .write_u64 = cpuset_write_u64,
                  .private = FILE_MEMORY_PRESSURE_ENABLED,
          },
  
          { }     /* terminate */
  };
  
  /*
   *      cpuset_css_alloc - allocate a cpuset css
   *      cont:   control group that the new cpuset will be part of
   */
  
  static struct cgroup_subsys_state *cpuset_css_alloc(struct cgroup *cont)
  {
          struct cgroup *parent_cg = cont->parent;
          struct cgroup *tmp_cg;
          struct cpuset *parent, *cs;
  
          if (!parent_cg)
                  return &top_cpuset.css;
          parent = cgroup_cs(parent_cg);
  
          cs = kmalloc(sizeof(*cs), GFP_KERNEL);
          if (!cs)
                  return ERR_PTR(-ENOMEM);
          if (!alloc_cpumask_var(&cs->cpus_allowed, GFP_KERNEL)) {
                  kfree(cs);
                  return ERR_PTR(-ENOMEM);
          }
  
          cs->flags = 0;
          if (is_spread_page(parent))
                  set_bit(CS_SPREAD_PAGE, &cs->flags);
          if (is_spread_slab(parent))
                  set_bit(CS_SPREAD_SLAB, &cs->flags);
          set_bit(CS_SCHED_LOAD_BALANCE, &cs->flags);
          cpumask_clear(cs->cpus_allowed);
          nodes_clear(cs->mems_allowed);
          fmeter_init(&cs->fmeter);
          cs->relax_domain_level = -1;
  
          cs->parent = parent;
          number_of_cpusets++;
  
          if (!test_bit(CGRP_CPUSET_CLONE_CHILDREN, &cont->flags))
                  goto skip_clone;
  
          /*
           * Clone @parent's configuration if CGRP_CPUSET_CLONE_CHILDREN is
           * set.  This flag handling is implemented in cgroup core for
           * histrical reasons - the flag may be specified during mount.
           *
           * Currently, if any sibling cpusets have exclusive cpus or mem, we
           * refuse to clone the configuration - thereby refusing the task to
           * be entered, and as a result refusing the sys_unshare() or
           * clone() which initiated it.  If this becomes a problem for some
           * users who wish to allow that scenario, then this could be
           * changed to grant parent->cpus_allowed-sibling_cpus_exclusive
           * (and likewise for mems) to the new cgroup.
           */
          list_for_each_entry(tmp_cg, &parent_cg->children, sibling) {
                  struct cpuset *tmp_cs = cgroup_cs(tmp_cg);
  
                  if (is_mem_exclusive(tmp_cs) || is_cpu_exclusive(tmp_cs))
                          goto skip_clone;
          }
  
          mutex_lock(&callback_mutex);
          cs->mems_allowed = parent->mems_allowed;
          cpumask_copy(cs->cpus_allowed, parent->cpus_allowed);
          mutex_unlock(&callback_mutex);
  skip_clone:
          return &cs->css;
  }
  
  /*
   * If the cpuset being removed has its flag 'sched_load_balance'
   * enabled, then simulate turning sched_load_balance off, which
   * will call async_rebuild_sched_domains().
   */
  
  static void cpuset_css_free(struct cgroup *cont)
  {
          struct cpuset *cs = cgroup_cs(cont);
  
          if (is_sched_load_balance(cs))
                  update_flag(CS_SCHED_LOAD_BALANCE, cs, 0);
  
          number_of_cpusets--;
          free_cpumask_var(cs->cpus_allowed);
          kfree(cs);
  }
  
  struct cgroup_subsys cpuset_subsys = {
          .name = "cpuset",
          .css_alloc = cpuset_css_alloc,
          .css_free = cpuset_css_free,
          .can_attach = cpuset_can_attach,
          .attach = cpuset_attach,
          .subsys_id = cpuset_subsys_id,
          .base_cftypes = files,
          .early_init = 1,
  };
  
  /**
   * cpuset_init - initialize cpusets at system boot
   *
   * Description: Initialize top_cpuset and the cpuset internal file system,
   **/
  
  int __init cpuset_init(void)
  {
          int err = 0;
  
          if (!alloc_cpumask_var(&top_cpuset.cpus_allowed, GFP_KERNEL))
                  BUG();
  
          cpumask_setall(top_cpuset.cpus_allowed);
          nodes_setall(top_cpuset.mems_allowed);
  
          fmeter_init(&top_cpuset.fmeter);
          set_bit(CS_SCHED_LOAD_BALANCE, &top_cpuset.flags);
          top_cpuset.relax_domain_level = -1;
  
          err = register_filesystem(&cpuset_fs_type);
          if (err < 0)
                  return err;
  
          if (!alloc_cpumask_var(&cpus_attach, GFP_KERNEL))
                  BUG();
  
          number_of_cpusets = 1;
          return 0;
  }
  
  /**
   * cpuset_do_move_task - move a given task to another cpuset
   * @tsk: pointer to task_struct the task to move
   * @scan: struct cgroup_scanner contained in its struct cpuset_hotplug_scanner
   *
   * Called by cgroup_scan_tasks() for each task in a cgroup.
   * Return nonzero to stop the walk through the tasks.
   */
  static void cpuset_do_move_task(struct task_struct *tsk,
                                  struct cgroup_scanner *scan)
  {
          struct cgroup *new_cgroup = scan->data;
  
          cgroup_attach_task(new_cgroup, tsk);
  }
  
  /**
   * move_member_tasks_to_cpuset - move tasks from one cpuset to another
   * @from: cpuset in which the tasks currently reside
   * @to: cpuset to which the tasks will be moved
   *
   * Called with cgroup_mutex held
   * callback_mutex must not be held, as cpuset_attach() will take it.
   *
   * The cgroup_scan_tasks() function will scan all the tasks in a cgroup,
   * calling callback functions for each.
   */
  static void move_member_tasks_to_cpuset(struct cpuset *from, struct cpuset *to)
  {
          struct cgroup_scanner scan;
  
          scan.cg = from->css.cgroup;
          scan.test_task = NULL; /* select all tasks in cgroup */
          scan.process_task = cpuset_do_move_task;
          scan.heap = NULL;
          scan.data = to->css.cgroup;
  
          if (cgroup_scan_tasks(&scan))
                  printk(KERN_ERR "move_member_tasks_to_cpuset: "
                                  "cgroup_scan_tasks failed\n");
  }
  
  /*
   * If CPU and/or memory hotplug handlers, below, unplug any CPUs
   * or memory nodes, we need to walk over the cpuset hierarchy,
   * removing that CPU or node from all cpusets.  If this removes the
   * last CPU or node from a cpuset, then move the tasks in the empty
   * cpuset to its next-highest non-empty parent.
   *
   * Called with cgroup_mutex held
   * callback_mutex must not be held, as cpuset_attach() will take it.
   */
  static void remove_tasks_in_empty_cpuset(struct cpuset *cs)
  {
          struct cpuset *parent;
  
          /*
           * The cgroup's css_sets list is in use if there are tasks
           * in the cpuset; the list is empty if there are none;
           * the cs->css.refcnt seems always 0.
           */
          if (list_empty(&cs->css.cgroup->css_sets))
                  return;
  
          /*
           * Find its next-highest non-empty parent, (top cpuset
           * has online cpus, so can't be empty).
           */
          parent = cs->parent;
          while (cpumask_empty(parent->cpus_allowed) ||
                          nodes_empty(parent->mems_allowed))
                  parent = parent->parent;
  
          move_member_tasks_to_cpuset(cs, parent);
  }
  
  /*
   * Helper function to traverse cpusets.
   * It can be used to walk the cpuset tree from top to bottom, completing
   * one layer before dropping down to the next (thus always processing a
   * node before any of its children).
   */
  static struct cpuset *cpuset_next(struct list_head *queue)
  {
          struct cpuset *cp;
          struct cpuset *child;   /* scans child cpusets of cp */
          struct cgroup *cont;
  
          if (list_empty(queue))
                  return NULL;
  
          cp = list_first_entry(queue, struct cpuset, stack_list);
          list_del(queue->next);
          list_for_each_entry(cont, &cp->css.cgroup->children, sibling) {
                  child = cgroup_cs(cont);
                  list_add_tail(&child->stack_list, queue);
          }
  
          return cp;
  }
  
  
  /*
   * Walk the specified cpuset subtree upon a hotplug operation (CPU/Memory
   * online/offline) and update the cpusets accordingly.
   * For regular CPU/Mem hotplug, look for empty cpusets; the tasks of such
   * cpuset must be moved to a parent cpuset.
   *
   * Called with cgroup_mutex held.  We take callback_mutex to modify
   * cpus_allowed and mems_allowed.
   *
   * This walk processes the tree from top to bottom, completing one layer
   * before dropping down to the next.  It always processes a node before
   * any of its children.
   *
   * In the case of memory hot-unplug, it will remove nodes from N_MEMORY
   * if all present pages from a node are offlined.
   */
  static void
  scan_cpusets_upon_hotplug(struct cpuset *root, enum hotplug_event event)
  {
          LIST_HEAD(queue);
          struct cpuset *cp;              /* scans cpusets being updated */
          static nodemask_t oldmems;      /* protected by cgroup_mutex */
  
          list_add_tail((struct list_head *)&root->stack_list, &queue);
  
          switch (event) {
          case CPUSET_CPU_OFFLINE:
                  while ((cp = cpuset_next(&queue)) != NULL) {
  
                          /* Continue past cpusets with all cpus online */
                          if (cpumask_subset(cp->cpus_allowed, cpu_active_mask))
                                  continue;
  
                          /* Remove offline cpus from this cpuset. */
                          mutex_lock(&callback_mutex);
                          cpumask_and(cp->cpus_allowed, cp->cpus_allowed,
                                                          cpu_active_mask);
                          mutex_unlock(&callback_mutex);
  
                          /* Move tasks from the empty cpuset to a parent */
                          if (cpumask_empty(cp->cpus_allowed))
                                  remove_tasks_in_empty_cpuset(cp);
                          else
                                  update_tasks_cpumask(cp, NULL);
                  }
                  break;
  
          case CPUSET_MEM_OFFLINE:
                  while ((cp = cpuset_next(&queue)) != NULL) {
  
                          /* Continue past cpusets with all mems online */
                          if (nodes_subset(cp->mems_allowed,
                                          node_states[N_MEMORY]))
                                  continue;
  
                          oldmems = cp->mems_allowed;
  
                          /* Remove offline mems from this cpuset. */
                          mutex_lock(&callback_mutex);
                          nodes_and(cp->mems_allowed, cp->mems_allowed,
                                                  node_states[N_MEMORY]);
                          mutex_unlock(&callback_mutex);
  
                          /* Move tasks from the empty cpuset to a parent */
                          if (nodes_empty(cp->mems_allowed))
                                  remove_tasks_in_empty_cpuset(cp);
                          else
                                  update_tasks_nodemask(cp, &oldmems, NULL);
                  }
          }
  }
  
  /*
   * The top_cpuset tracks what CPUs and Memory Nodes are online,
   * period.  This is necessary in order to make cpusets transparent
   * (of no affect) on systems that are actively using CPU hotplug
   * but making no active use of cpusets.
   *
   * The only exception to this is suspend/resume, where we don't
   * modify cpusets at all.
   *
   * This routine ensures that top_cpuset.cpus_allowed tracks
   * cpu_active_mask on each CPU hotplug (cpuhp) event.
   *
   * Called within get_online_cpus().  Needs to call cgroup_lock()
   * before calling generate_sched_domains().
   *
   * @cpu_online: Indicates whether this is a CPU online event (true) or
   * a CPU offline event (false).
   */
  void cpuset_update_active_cpus(bool cpu_online)
  {
          struct sched_domain_attr *attr;
          cpumask_var_t *doms;
          int ndoms;
  
          cgroup_lock();
          mutex_lock(&callback_mutex);
          cpumask_copy(top_cpuset.cpus_allowed, cpu_active_mask);
          mutex_unlock(&callback_mutex);
  
          if (!cpu_online)
                  scan_cpusets_upon_hotplug(&top_cpuset, CPUSET_CPU_OFFLINE);
  
          ndoms = generate_sched_domains(&doms, &attr);
          cgroup_unlock();
  
          /* Have scheduler rebuild the domains */
          partition_sched_domains(ndoms, doms, attr);
  }
  
  #ifdef CONFIG_MEMORY_HOTPLUG
  /*
   * Keep top_cpuset.mems_allowed tracking node_states[N_MEMORY].
   * Call this routine anytime after node_states[N_MEMORY] changes.
   * See cpuset_update_active_cpus() for CPU hotplug handling.
   */
  static int cpuset_track_online_nodes(struct notifier_block *self,
                                  unsigned long action, void *arg)
  {
          static nodemask_t oldmems;      /* protected by cgroup_mutex */
  
          cgroup_lock();
          switch (action) {
          case MEM_ONLINE:
                  oldmems = top_cpuset.mems_allowed;
                  mutex_lock(&callback_mutex);
                  top_cpuset.mems_allowed = node_states[N_MEMORY];
                  mutex_unlock(&callback_mutex);
                  update_tasks_nodemask(&top_cpuset, &oldmems, NULL);
                  break;
          case MEM_OFFLINE:
                  /*
                   * needn't update top_cpuset.mems_allowed explicitly because
                   * scan_cpusets_upon_hotplug() will update it.
                   */
                  scan_cpusets_upon_hotplug(&top_cpuset, CPUSET_MEM_OFFLINE);
                  break;
          default:
                  break;
          }
          cgroup_unlock();
  
          return NOTIFY_OK;
  }
  #endif
  
  /**
   * cpuset_init_smp - initialize cpus_allowed
   *
   * Description: Finish top cpuset after cpu, node maps are initialized
   **/
  
  void __init cpuset_init_smp(void)
  {
          cpumask_copy(top_cpuset.cpus_allowed, cpu_active_mask);
          top_cpuset.mems_allowed = node_states[N_MEMORY];
  
          hotplug_memory_notifier(cpuset_track_online_nodes, 10);
  
          cpuset_wq = create_singlethread_workqueue("cpuset");
          BUG_ON(!cpuset_wq);
  }
  
  /**
   * cpuset_cpus_allowed - return cpus_allowed mask from a tasks cpuset.
   * @tsk: pointer to task_struct from which to obtain cpuset->cpus_allowed.
   * @pmask: pointer to struct cpumask variable to receive cpus_allowed set.
   *
   * Description: Returns the cpumask_var_t cpus_allowed of the cpuset
   * attached to the specified @tsk.  Guaranteed to return some non-empty
   * subset of cpu_online_mask, even if this means going outside the
   * tasks cpuset.
   **/
  
  void cpuset_cpus_allowed(struct task_struct *tsk, struct cpumask *pmask)
  {
          mutex_lock(&callback_mutex);
          task_lock(tsk);
          guarantee_online_cpus(task_cs(tsk), pmask);
          task_unlock(tsk);
          mutex_unlock(&callback_mutex);
  }
  
  void cpuset_cpus_allowed_fallback(struct task_struct *tsk)
  {
          const struct cpuset *cs;
  
          rcu_read_lock();
          cs = task_cs(tsk);
          if (cs)
                  do_set_cpus_allowed(tsk, cs->cpus_allowed);
          rcu_read_unlock();
  
          /*
           * We own tsk->cpus_allowed, nobody can change it under us.
           *
           * But we used cs && cs->cpus_allowed lockless and thus can
           * race with cgroup_attach_task() or update_cpumask() and get
           * the wrong tsk->cpus_allowed. However, both cases imply the
           * subsequent cpuset_change_cpumask()->set_cpus_allowed_ptr()
           * which takes task_rq_lock().
           *
           * If we are called after it dropped the lock we must see all
           * changes in tsk_cs()->cpus_allowed. Otherwise we can temporary
           * set any mask even if it is not right from task_cs() pov,
           * the pending set_cpus_allowed_ptr() will fix things.
           *
           * select_fallback_rq() will fix things ups and set cpu_possible_mask
           * if required.
           */
  }
  
  void cpuset_init_current_mems_allowed(void)
  {
          nodes_setall(current->mems_allowed);
  }
  
  /**
   * cpuset_mems_allowed - return mems_allowed mask from a tasks cpuset.
   * @tsk: pointer to task_struct from which to obtain cpuset->mems_allowed.
   *
   * Description: Returns the nodemask_t mems_allowed of the cpuset
   * attached to the specified @tsk.  Guaranteed to return some non-empty
   * subset of node_states[N_MEMORY], even if this means going outside the
   * tasks cpuset.
   **/
  
  nodemask_t cpuset_mems_allowed(struct task_struct *tsk)
  {
          nodemask_t mask;
  
          mutex_lock(&callback_mutex);
          task_lock(tsk);
          guarantee_online_mems(task_cs(tsk), &mask);
          task_unlock(tsk);
          mutex_unlock(&callback_mutex);
  
          return mask;
  }
  
  /**
   * cpuset_nodemask_valid_mems_allowed - check nodemask vs. curremt mems_allowed
   * @nodemask: the nodemask to be checked
   *
   * Are any of the nodes in the nodemask allowed in current->mems_allowed?
   */
  int cpuset_nodemask_valid_mems_allowed(nodemask_t *nodemask)
  {
          return nodes_intersects(*nodemask, current->mems_allowed);
  }
  
  /*
   * nearest_hardwall_ancestor() - Returns the nearest mem_exclusive or
   * mem_hardwall ancestor to the specified cpuset.  Call holding
   * callback_mutex.  If no ancestor is mem_exclusive or mem_hardwall
   * (an unusual configuration), then returns the root cpuset.
   */
  static const struct cpuset *nearest_hardwall_ancestor(const struct cpuset *cs)
  {
          while (!(is_mem_exclusive(cs) || is_mem_hardwall(cs)) && cs->parent)
                  cs = cs->parent;
          return cs;
  }
  
  /**
   * cpuset_node_allowed_softwall - Can we allocate on a memory node?
   * @node: is this an allowed node?
   * @gfp_mask: memory allocation flags
   *
   * If we're in interrupt, yes, we can always allocate.  If __GFP_THISNODE is
   * set, yes, we can always allocate.  If node is in our task's mems_allowed,
   * yes.  If it's not a __GFP_HARDWALL request and this node is in the nearest
   * hardwalled cpuset ancestor to this task's cpuset, yes.  If the task has been
   * OOM killed and has access to memory reserves as specified by the TIF_MEMDIE
   * flag, yes.
   * Otherwise, no.
   *
   * If __GFP_HARDWALL is set, cpuset_node_allowed_softwall() reduces to
   * cpuset_node_allowed_hardwall().  Otherwise, cpuset_node_allowed_softwall()
   * might sleep, and might allow a node from an enclosing cpuset.
   *
   * cpuset_node_allowed_hardwall() only handles the simpler case of hardwall
   * cpusets, and never sleeps.
   *
   * The __GFP_THISNODE placement logic is really handled elsewhere,
   * by forcibly using a zonelist starting at a specified node, and by
   * (in get_page_from_freelist()) refusing to consider the zones for
   * any node on the zonelist except the first.  By the time any such
   * calls get to this routine, we should just shut up and say 'yes'.
   *
   * GFP_USER allocations are marked with the __GFP_HARDWALL bit,
   * and do not allow allocations outside the current tasks cpuset
   * unless the task has been OOM killed as is marked TIF_MEMDIE.
   * GFP_KERNEL allocations are not so marked, so can escape to the
   * nearest enclosing hardwalled ancestor cpuset.
   *
   * Scanning up parent cpusets requires callback_mutex.  The
   * __alloc_pages() routine only calls here with __GFP_HARDWALL bit
   * _not_ set if it's a GFP_KERNEL allocation, and all nodes in the
   * current tasks mems_allowed came up empty on the first pass over
   * the zonelist.  So only GFP_KERNEL allocations, if all nodes in the
   * cpuset are short of memory, might require taking the callback_mutex
   * mutex.
   *
   * The first call here from mm/page_alloc:get_page_from_freelist()
   * has __GFP_HARDWALL set in gfp_mask, enforcing hardwall cpusets,
   * so no allocation on a node outside the cpuset is allowed (unless
   * in interrupt, of course).
   *
   * The second pass through get_page_from_freelist() doesn't even call
   * here for GFP_ATOMIC calls.  For those calls, the __alloc_pages()
   * variable 'wait' is not set, and the bit ALLOC_CPUSET is not set
   * in alloc_flags.  That logic and the checks below have the combined
   * affect that:
   *      in_interrupt - any node ok (current task context irrelevant)
   *      GFP_ATOMIC   - any node ok
   *      TIF_MEMDIE   - any node ok
   *      GFP_KERNEL   - any node in enclosing hardwalled cpuset ok
   *      GFP_USER     - only nodes in current tasks mems allowed ok.
   *
   * Rule:
   *    Don't call cpuset_node_allowed_softwall if you can't sleep, unless you
   *    pass in the __GFP_HARDWALL flag set in gfp_flag, which disables
   *    the code that might scan up ancestor cpusets and sleep.
   */
  int __cpuset_node_allowed_softwall(int node, gfp_t gfp_mask)
  {
          const struct cpuset *cs;        /* current cpuset ancestors */
          int allowed;                    /* is allocation in zone z allowed? */
  
          if (in_interrupt() || (gfp_mask & __GFP_THISNODE))
                  return 1;
          might_sleep_if(!(gfp_mask & __GFP_HARDWALL));
          if (node_isset(node, current->mems_allowed))
                  return 1;
          /*
           * Allow tasks that have access to memory reserves because they have
           * been OOM killed to get memory anywhere.
           */
          if (unlikely(test_thread_flag(TIF_MEMDIE)))
                  return 1;
          if (gfp_mask & __GFP_HARDWALL)  /* If hardwall request, stop here */
                  return 0;
  
          if (current->flags & PF_EXITING) /* Let dying task have memory */
                  return 1;
  
          /* Not hardwall and node outside mems_allowed: scan up cpusets */
          mutex_lock(&callback_mutex);
  
          task_lock(current);
          cs = nearest_hardwall_ancestor(task_cs(current));
          task_unlock(current);
  
          allowed = node_isset(node, cs->mems_allowed);
          mutex_unlock(&callback_mutex);
          return allowed;
  }
  
  /*
   * cpuset_node_allowed_hardwall - Can we allocate on a memory node?
   * @node: is this an allowed node?
   * @gfp_mask: memory allocation flags
   *
   * If we're in interrupt, yes, we can always allocate.  If __GFP_THISNODE is
   * set, yes, we can always allocate.  If node is in our task's mems_allowed,
   * yes.  If the task has been OOM killed and has access to memory reserves as
   * specified by the TIF_MEMDIE flag, yes.
   * Otherwise, no.
   *
   * The __GFP_THISNODE placement logic is really handled elsewhere,
   * by forcibly using a zonelist starting at a specified node, and by
   * (in get_page_from_freelist()) refusing to consider the zones for
   * any node on the zonelist except the first.  By the time any such
   * calls get to this routine, we should just shut up and say 'yes'.
   *
   * Unlike the cpuset_node_allowed_softwall() variant, above,
   * this variant requires that the node be in the current task's
   * mems_allowed or that we're in interrupt.  It does not scan up the
   * cpuset hierarchy for the nearest enclosing mem_exclusive cpuset.
   * It never sleeps.
   */
  int __cpuset_node_allowed_hardwall(int node, gfp_t gfp_mask)
  {
          if (in_interrupt() || (gfp_mask & __GFP_THISNODE))
                  return 1;
          if (node_isset(node, current->mems_allowed))
                  return 1;
          /*
           * Allow tasks that have access to memory reserves because they have
           * been OOM killed to get memory anywhere.
           */
          if (unlikely(test_thread_flag(TIF_MEMDIE)))
                  return 1;
          return 0;
  }
  
  /**
   * cpuset_unlock - release lock on cpuset changes
   *
   * Undo the lock taken in a previous cpuset_lock() call.
   */
  
  void cpuset_unlock(void)
  {
          mutex_unlock(&callback_mutex);
  }
  
  /**
   * cpuset_mem_spread_node() - On which node to begin search for a file page
   * cpuset_slab_spread_node() - On which node to begin search for a slab page
   *
   * If a task is marked PF_SPREAD_PAGE or PF_SPREAD_SLAB (as for
   * tasks in a cpuset with is_spread_page or is_spread_slab set),
   * and if the memory allocation used cpuset_mem_spread_node()
   * to determine on which node to start looking, as it will for
   * certain page cache or slab cache pages such as used for file
   * system buffers and inode caches, then instead of starting on the
   * local node to look for a free page, rather spread the starting
   * node around the tasks mems_allowed nodes.
   *
   * We don't have to worry about the returned node being offline
   * because "it can't happen", and even if it did, it would be ok.
   *
   * The routines calling guarantee_online_mems() are careful to
   * only set nodes in task->mems_allowed that are online.  So it
   * should not be possible for the following code to return an
   * offline node.  But if it did, that would be ok, as this routine
   * is not returning the node where the allocation must be, only
   * the node where the search should start.  The zonelist passed to
   * __alloc_pages() will include all nodes.  If the slab allocator
   * is passed an offline node, it will fall back to the local node.
   * See kmem_cache_alloc_node().
   */
  
  static int cpuset_spread_node(int *rotor)
  {
          int node;
  
          node = next_node(*rotor, current->mems_allowed);
          if (node == MAX_NUMNODES)
                  node = first_node(current->mems_allowed);
          *rotor = node;
          return node;
  }
  
  int cpuset_mem_spread_node(void)
  {
          if (current->cpuset_mem_spread_rotor == NUMA_NO_NODE)
                  current->cpuset_mem_spread_rotor =
                          node_random(&current->mems_allowed);
  
          return cpuset_spread_node(&current->cpuset_mem_spread_rotor);
  }
  
  int cpuset_slab_spread_node(void)
  {
          if (current->cpuset_slab_spread_rotor == NUMA_NO_NODE)
                  current->cpuset_slab_spread_rotor =
                          node_random(&current->mems_allowed);
  
          return cpuset_spread_node(&current->cpuset_slab_spread_rotor);
  }
  
  EXPORT_SYMBOL_GPL(cpuset_mem_spread_node);
  
  /**
   * cpuset_mems_allowed_intersects - Does @tsk1's mems_allowed intersect @tsk2's?
   * @tsk1: pointer to task_struct of some task.
   * @tsk2: pointer to task_struct of some other task.
   *
   * Description: Return true if @tsk1's mems_allowed intersects the
   * mems_allowed of @tsk2.  Used by the OOM killer to determine if
   * one of the task's memory usage might impact the memory available
   * to the other.
   **/
  
  int cpuset_mems_allowed_intersects(const struct task_struct *tsk1,
                                     const struct task_struct *tsk2)
  {
          return nodes_intersects(tsk1->mems_allowed, tsk2->mems_allowed);
  }
  
  /**
   * cpuset_print_task_mems_allowed - prints task's cpuset and mems_allowed
   * @task: pointer to task_struct of some task.
   *
   * Description: Prints @task's name, cpuset name, and cached copy of its
   * mems_allowed to the kernel log.  Must hold task_lock(task) to allow
   * dereferencing task_cs(task).
   */
  void cpuset_print_task_mems_allowed(struct task_struct *tsk)
  {
          struct dentry *dentry;
  
          dentry = task_cs(tsk)->css.cgroup->dentry;
          spin_lock(&cpuset_buffer_lock);
          snprintf(cpuset_name, CPUSET_NAME_LEN,
                   dentry ? (const char *)dentry->d_name.name : "/");
          nodelist_scnprintf(cpuset_nodelist, CPUSET_NODELIST_LEN,
                             tsk->mems_allowed);
          printk(KERN_INFO "%s cpuset=%s mems_allowed=%s\n",
                 tsk->comm, cpuset_name, cpuset_nodelist);
          spin_unlock(&cpuset_buffer_lock);
  }
  
  /*
   * Collection of memory_pressure is suppressed unless
   * this flag is enabled by writing "1" to the special
   * cpuset file 'memory_pressure_enabled' in the root cpuset.
   */
  
  int cpuset_memory_pressure_enabled __read_mostly;
  
  /**
   * cpuset_memory_pressure_bump - keep stats of per-cpuset reclaims.
   *
   * Keep a running average of the rate of synchronous (direct)
   * page reclaim efforts initiated by tasks in each cpuset.
   *
   * This represents the rate at which some task in the cpuset
   * ran low on memory on all nodes it was allowed to use, and
   * had to enter the kernels page reclaim code in an effort to
   * create more free memory by tossing clean pages or swapping
   * or writing dirty pages.
   *
   * Display to user space in the per-cpuset read-only file
   * "memory_pressure".  Value displayed is an integer
   * representing the recent rate of entry into the synchronous
   * (direct) page reclaim by any task attached to the cpuset.
   **/
  
  void __cpuset_memory_pressure_bump(void)
  {
          task_lock(current);
          fmeter_markevent(&task_cs(current)->fmeter);
          task_unlock(current);
  }
  
  #ifdef CONFIG_PROC_PID_CPUSET
  /*
   * proc_cpuset_show()
   *  - Print tasks cpuset path into seq_file.
   *  - Used for /proc/<pid>/cpuset.
   *  - No need to task_lock(tsk) on this tsk->cpuset reference, as it
   *    doesn't really matter if tsk->cpuset changes after we read it,
   *    and we take cgroup_mutex, keeping cpuset_attach() from changing it
   *    anyway.
   */
  static int proc_cpuset_show(struct seq_file *m, void *unused_v)
  {
          struct pid *pid;
          struct task_struct *tsk;
          char *buf;
          struct cgroup_subsys_state *css;
          int retval;
  
          retval = -ENOMEM;
          buf = kmalloc(PAGE_SIZE, GFP_KERNEL);
          if (!buf)
                  goto out;
  
          retval = -ESRCH;
          pid = m->private;
          tsk = get_pid_task(pid, PIDTYPE_PID);
          if (!tsk)
                  goto out_free;
  
          retval = -EINVAL;
          cgroup_lock();
          css = task_subsys_state(tsk, cpuset_subsys_id);
          retval = cgroup_path(css->cgroup, buf, PAGE_SIZE);
          if (retval < 0)
                  goto out_unlock;
          seq_puts(m, buf);
          seq_putc(m, '\n');
  out_unlock:
          cgroup_unlock();
          put_task_struct(tsk);
  out_free:
          kfree(buf);
  out:
          return retval;
  }
  
  static int cpuset_open(struct inode *inode, struct file *file)
  {
          struct pid *pid = PROC_I(inode)->pid;
          return single_open(file, proc_cpuset_show, pid);
  }
  
  const struct file_operations proc_cpuset_operations = {
          .open           = cpuset_open,
          .read           = seq_read,
          .llseek         = seq_lseek,
          .release        = single_release,
  };
  #endif /* CONFIG_PROC_PID_CPUSET */
  
  /* Display task mems_allowed in /proc/<pid>/status file. */
  void cpuset_task_status_allowed(struct seq_file *m, struct task_struct *task)
  {
          seq_printf(m, "Mems_allowed:\t");
          seq_nodemask(m, &task->mems_allowed);
          seq_printf(m, "\n");
          seq_printf(m, "Mems_allowed_list:\t");
          seq_nodemask_list(m, &task->mems_allowed);
          seq_printf(m, "\n");
  }

Cache object: b50f4d9c8e2aea77d73153080c54a166