The Design and Implementation of the FreeBSD Operating System, Second Edition
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FreeBSD/Linux Kernel Cross Reference
sys/vm/uma_int.h

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    1 /*-
    2  * Copyright (c) 2004, 2005,
    3  *     Bosko Milekic <bmilekic@FreeBSD.org>.  All rights reserved.
    4  * Copyright (c) 2002, 2003, 2004, 2005,
    5  *     Jeffrey Roberson <jeff@FreeBSD.org>.  All rights reserved.
    6  *
    7  * Redistribution and use in source and binary forms, with or without
    8  * modification, are permitted provided that the following conditions
    9  * are met:
   10  * 1. Redistributions of source code must retain the above copyright
   11  *    notice unmodified, this list of conditions, and the following
   12  *    disclaimer.
   13  * 2. Redistributions in binary form must reproduce the above copyright
   14  *    notice, this list of conditions and the following disclaimer in the
   15  *    documentation and/or other materials provided with the distribution.
   16  *
   17  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
   18  * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
   19  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
   20  * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
   21  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
   22  * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
   23  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
   24  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
   25  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
   26  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
   27  *
   28  * $FreeBSD: src/sys/vm/uma_int.h,v 1.25.2.4 2005/02/16 21:53:08 bmilekic Exp $
   29  *
   30  */
   31 
   32 /* 
   33  * This file includes definitions, structures, prototypes, and inlines that
   34  * should not be used outside of the actual implementation of UMA.
   35  */
   36 
   37 /* 
   38  * Here's a quick description of the relationship between the objects:
   39  *
   40  * Kegs contain lists of slabs which are stored in either the full bin, empty
   41  * bin, or partially allocated bin, to reduce fragmentation.  They also contain
   42  * the user supplied value for size, which is adjusted for alignment purposes
   43  * and rsize is the result of that.  The Keg also stores information for
   44  * managing a hash of page addresses that maps pages to uma_slab_t structures
   45  * for pages that don't have embedded uma_slab_t's.
   46  *  
   47  * The uma_slab_t may be embedded in a UMA_SLAB_SIZE chunk of memory or it may
   48  * be allocated off the page from a special slab zone.  The free list within a
   49  * slab is managed with a linked list of indexes, which are 8 bit values.  If
   50  * UMA_SLAB_SIZE is defined to be too large I will have to switch to 16bit
   51  * values.  Currently on alpha you can get 250 or so 32 byte items and on x86
   52  * you can get 250 or so 16byte items.  For item sizes that would yield more
   53  * than 10% memory waste we potentially allocate a separate uma_slab_t if this
   54  * will improve the number of items per slab that will fit.  
   55  *
   56  * Other potential space optimizations are storing the 8bit of linkage in space
   57  * wasted between items due to alignment problems.  This may yield a much better
   58  * memory footprint for certain sizes of objects.  Another alternative is to
   59  * increase the UMA_SLAB_SIZE, or allow for dynamic slab sizes.  I prefer
   60  * dynamic slab sizes because we could stick with 8 bit indexes and only use
   61  * large slab sizes for zones with a lot of waste per slab.  This may create
   62  * ineffeciencies in the vm subsystem due to fragmentation in the address space.
   63  *
   64  * The only really gross cases, with regards to memory waste, are for those
   65  * items that are just over half the page size.   You can get nearly 50% waste,
   66  * so you fall back to the memory footprint of the power of two allocator. I
   67  * have looked at memory allocation sizes on many of the machines available to
   68  * me, and there does not seem to be an abundance of allocations at this range
   69  * so at this time it may not make sense to optimize for it.  This can, of 
   70  * course, be solved with dynamic slab sizes.
   71  *
   72  * Kegs may serve multiple Zones but by far most of the time they only serve
   73  * one.  When a Zone is created, a Keg is allocated and setup for it.  While
   74  * the backing Keg stores slabs, the Zone caches Buckets of items allocated
   75  * from the slabs.  Each Zone is equipped with an init/fini and ctor/dtor
   76  * pair, as well as with its own set of small per-CPU caches, layered above
   77  * the Zone's general Bucket cache.
   78  *
   79  * The PCPU caches are protected by their own locks, while the Zones backed
   80  * by the same Keg all share a common Keg lock (to coalesce contention on
   81  * the backing slabs).  The backing Keg typically only serves one Zone but
   82  * in the case of multiple Zones, one of the Zones is considered the
   83  * Master Zone and all Zone-related stats from the Keg are done in the
   84  * Master Zone.  For an example of a Multi-Zone setup, refer to the
   85  * Mbuf allocation code.
   86  */
   87 
   88 /*
   89  *      This is the representation for normal (Non OFFPAGE slab)
   90  *
   91  *      i == item
   92  *      s == slab pointer
   93  *
   94  *      <----------------  Page (UMA_SLAB_SIZE) ------------------>
   95  *      ___________________________________________________________
   96  *     | _  _  _  _  _  _  _  _  _  _  _  _  _  _  _   ___________ |
   97  *     ||i||i||i||i||i||i||i||i||i||i||i||i||i||i||i| |slab header||
   98  *     ||_||_||_||_||_||_||_||_||_||_||_||_||_||_||_| |___________|| 
   99  *     |___________________________________________________________|
  100  *
  101  *
  102  *      This is an OFFPAGE slab. These can be larger than UMA_SLAB_SIZE.
  103  *
  104  *      ___________________________________________________________
  105  *     | _  _  _  _  _  _  _  _  _  _  _  _  _  _  _  _  _  _  _   |
  106  *     ||i||i||i||i||i||i||i||i||i||i||i||i||i||i||i||i||i||i||i|  |
  107  *     ||_||_||_||_||_||_||_||_||_||_||_||_||_||_||_||_||_||_||_|  |
  108  *     |___________________________________________________________|
  109  *       ___________    ^
  110  *      |slab header|   |
  111  *      |___________|---*
  112  *
  113  */
  114 
  115 #ifndef VM_UMA_INT_H
  116 #define VM_UMA_INT_H
  117 
  118 #define UMA_SLAB_SIZE   PAGE_SIZE       /* How big are our slabs? */
  119 #define UMA_SLAB_MASK   (PAGE_SIZE - 1) /* Mask to get back to the page */
  120 #define UMA_SLAB_SHIFT  PAGE_SHIFT      /* Number of bits PAGE_MASK */
  121 
  122 #define UMA_BOOT_PAGES          40      /* Pages allocated for startup */
  123 
  124 /* Max waste before going to off page slab management */
  125 #define UMA_MAX_WASTE   (UMA_SLAB_SIZE / 10)
  126 
  127 /*
  128  * I doubt there will be many cases where this is exceeded. This is the initial
  129  * size of the hash table for uma_slabs that are managed off page. This hash
  130  * does expand by powers of two.  Currently it doesn't get smaller.
  131  */
  132 #define UMA_HASH_SIZE_INIT      32              
  133 
  134 /* 
  135  * I should investigate other hashing algorithms.  This should yield a low
  136  * number of collisions if the pages are relatively contiguous.
  137  *
  138  * This is the same algorithm that most processor caches use.
  139  *
  140  * I'm shifting and masking instead of % because it should be faster.
  141  */
  142 
  143 #define UMA_HASH(h, s) ((((unsigned long)s) >> UMA_SLAB_SHIFT) &        \
  144     (h)->uh_hashmask)
  145 
  146 #define UMA_HASH_INSERT(h, s, mem)                                      \
  147                 SLIST_INSERT_HEAD(&(h)->uh_slab_hash[UMA_HASH((h),      \
  148                     (mem))], (s), us_hlink);
  149 #define UMA_HASH_REMOVE(h, s, mem)                                      \
  150                 SLIST_REMOVE(&(h)->uh_slab_hash[UMA_HASH((h),           \
  151                     (mem))], (s), uma_slab, us_hlink);
  152 
  153 /* Hash table for freed address -> slab translation */
  154 
  155 SLIST_HEAD(slabhead, uma_slab);
  156 
  157 struct uma_hash {
  158         struct slabhead *uh_slab_hash;  /* Hash table for slabs */
  159         int             uh_hashsize;    /* Current size of the hash table */
  160         int             uh_hashmask;    /* Mask used during hashing */
  161 };
  162 
  163 /*
  164  * Structures for per cpu queues.
  165  */
  166 
  167 struct uma_bucket {
  168         LIST_ENTRY(uma_bucket)  ub_link;        /* Link into the zone */
  169         int16_t ub_cnt;                         /* Count of free items. */
  170         int16_t ub_entries;                     /* Max items. */
  171         void    *ub_bucket[];                   /* actual allocation storage */
  172 };
  173 
  174 typedef struct uma_bucket * uma_bucket_t;
  175 
  176 struct uma_cache {
  177         uma_bucket_t    uc_freebucket;  /* Bucket we're freeing to */
  178         uma_bucket_t    uc_allocbucket; /* Bucket to allocate from */
  179         u_int64_t       uc_allocs;      /* Count of allocations */
  180 };
  181 
  182 typedef struct uma_cache * uma_cache_t;
  183 
  184 /*
  185  * Keg management structure
  186  *
  187  * TODO: Optimize for cache line size
  188  *
  189  */
  190 struct uma_keg {
  191         LIST_ENTRY(uma_keg)     uk_link;        /* List of all kegs */
  192 
  193         struct mtx      uk_lock;        /* Lock for the keg */
  194         struct uma_hash uk_hash;
  195 
  196         LIST_HEAD(,uma_zone)    uk_zones;       /* Keg's zones */
  197         LIST_HEAD(,uma_slab)    uk_part_slab;   /* partially allocated slabs */
  198         LIST_HEAD(,uma_slab)    uk_free_slab;   /* empty slab list */
  199         LIST_HEAD(,uma_slab)    uk_full_slab;   /* full slabs */
  200 
  201         u_int32_t       uk_recurse;     /* Allocation recursion count */
  202         u_int32_t       uk_align;       /* Alignment mask */
  203         u_int32_t       uk_pages;       /* Total page count */
  204         u_int32_t       uk_free;        /* Count of items free in slabs */
  205         u_int32_t       uk_size;        /* Requested size of each item */
  206         u_int32_t       uk_rsize;       /* Real size of each item */
  207         u_int32_t       uk_maxpages;    /* Maximum number of pages to alloc */
  208 
  209         uma_init        uk_init;        /* Keg's init routine */
  210         uma_fini        uk_fini;        /* Keg's fini routine */
  211         uma_alloc       uk_allocf;      /* Allocation function */
  212         uma_free        uk_freef;       /* Free routine */
  213 
  214         struct vm_object        *uk_obj;        /* Zone specific object */
  215         vm_offset_t     uk_kva;         /* Base kva for zones with objs */
  216         uma_zone_t      uk_slabzone;    /* Slab zone backing us, if OFFPAGE */
  217 
  218         u_int16_t       uk_pgoff;       /* Offset to uma_slab struct */
  219         u_int16_t       uk_ppera;       /* pages per allocation from backend */
  220         u_int16_t       uk_ipers;       /* Items per slab */
  221         u_int16_t       uk_flags;       /* Internal flags */
  222 };
  223 
  224 /* Simpler reference to uma_keg for internal use. */
  225 typedef struct uma_keg * uma_keg_t;
  226 
  227 /* Page management structure */
  228 
  229 /* Sorry for the union, but space efficiency is important */
  230 struct uma_slab_head {
  231         uma_keg_t       us_keg;                 /* Keg we live in */
  232         union {
  233                 LIST_ENTRY(uma_slab)    _us_link;       /* slabs in zone */
  234                 unsigned long   _us_size;       /* Size of allocation */
  235         } us_type;
  236         SLIST_ENTRY(uma_slab)   us_hlink;       /* Link for hash table */
  237         u_int8_t        *us_data;               /* First item */
  238         u_int8_t        us_flags;               /* Page flags see uma.h */
  239         u_int8_t        us_freecount;   /* How many are free? */
  240         u_int8_t        us_firstfree;   /* First free item index */
  241 };
  242 
  243 /* The standard slab structure */
  244 struct uma_slab {
  245         struct uma_slab_head    us_head;        /* slab header data */
  246         struct {
  247                 u_int8_t        us_item;
  248         } us_freelist[1];                       /* actual number bigger */
  249 };
  250 
  251 /*
  252  * The slab structure for UMA_ZONE_REFCNT zones for whose items we
  253  * maintain reference counters in the slab for.
  254  */
  255 struct uma_slab_refcnt {
  256         struct uma_slab_head    us_head;        /* slab header data */
  257         struct {
  258                 u_int8_t        us_item;
  259                 u_int32_t       us_refcnt;
  260         } us_freelist[1];                       /* actual number bigger */
  261 };
  262 
  263 #define us_keg          us_head.us_keg
  264 #define us_link         us_head.us_type._us_link
  265 #define us_size         us_head.us_type._us_size
  266 #define us_hlink        us_head.us_hlink
  267 #define us_data         us_head.us_data
  268 #define us_flags        us_head.us_flags
  269 #define us_freecount    us_head.us_freecount
  270 #define us_firstfree    us_head.us_firstfree
  271 
  272 typedef struct uma_slab * uma_slab_t;
  273 typedef struct uma_slab_refcnt * uma_slabrefcnt_t;
  274 
  275 /*
  276  * These give us the size of one free item reference within our corresponding
  277  * uma_slab structures, so that our calculations during zone setup are correct
  278  * regardless of what the compiler decides to do with padding the structure
  279  * arrays within uma_slab.
  280  */
  281 #define UMA_FRITM_SZ    (sizeof(struct uma_slab) - sizeof(struct uma_slab_head))
  282 #define UMA_FRITMREF_SZ (sizeof(struct uma_slab_refcnt) -       \
  283     sizeof(struct uma_slab_head))
  284 
  285 /*
  286  * Zone management structure 
  287  *
  288  * TODO: Optimize for cache line size
  289  *
  290  */
  291 struct uma_zone {
  292         char            *uz_name;       /* Text name of the zone */
  293         struct mtx      *uz_lock;       /* Lock for the zone (keg's lock) */
  294         uma_keg_t       uz_keg;         /* Our underlying Keg */
  295 
  296         LIST_ENTRY(uma_zone)    uz_link;        /* List of all zones in keg */
  297         LIST_HEAD(,uma_bucket)  uz_full_bucket; /* full buckets */
  298         LIST_HEAD(,uma_bucket)  uz_free_bucket; /* Buckets for frees */
  299 
  300         uma_ctor        uz_ctor;        /* Constructor for each allocation */
  301         uma_dtor        uz_dtor;        /* Destructor */
  302         uma_init        uz_init;        /* Initializer for each item */
  303         uma_fini        uz_fini;        /* Discards memory */
  304 
  305         u_int64_t       uz_allocs;      /* Total number of allocations */
  306         uint16_t        uz_fills;       /* Outstanding bucket fills */
  307         uint16_t        uz_count;       /* Highest value ub_ptr can have */
  308 
  309         /*
  310          * This HAS to be the last item because we adjust the zone size
  311          * based on NCPU and then allocate the space for the zones.
  312          */
  313         struct uma_cache        uz_cpu[1];      /* Per cpu caches */
  314 };
  315 
  316 /*
  317  * These flags must not overlap with the UMA_ZONE flags specified in uma.h.
  318  */
  319 #define UMA_ZFLAG_PRIVALLOC     0x1000          /* Use uz_allocf. */
  320 #define UMA_ZFLAG_INTERNAL      0x2000          /* No offpage no PCPU. */
  321 #define UMA_ZFLAG_FULL          0x4000          /* Reached uz_maxpages */
  322 #define UMA_ZFLAG_CACHEONLY     0x8000          /* Don't ask VM for buckets. */
  323 
  324 /* Internal prototypes */
  325 static __inline uma_slab_t hash_sfind(struct uma_hash *hash, u_int8_t *data);
  326 void *uma_large_malloc(int size, int wait);
  327 void uma_large_free(uma_slab_t slab);
  328 
  329 /* Lock Macros */
  330 
  331 #define ZONE_LOCK_INIT(z, lc)                                   \
  332         do {                                                    \
  333                 if ((lc))                                       \
  334                         mtx_init((z)->uz_lock, (z)->uz_name,    \
  335                             (z)->uz_name, MTX_DEF | MTX_DUPOK); \
  336                 else                                            \
  337                         mtx_init((z)->uz_lock, (z)->uz_name,    \
  338                             "UMA zone", MTX_DEF | MTX_DUPOK);   \
  339         } while (0)
  340             
  341 #define ZONE_LOCK_FINI(z)       mtx_destroy((z)->uz_lock)
  342 #define ZONE_LOCK(z)    mtx_lock((z)->uz_lock)
  343 #define ZONE_UNLOCK(z)  mtx_unlock((z)->uz_lock)
  344 
  345 #define CPU_LOCK_INIT(cpu)                                      \
  346         mtx_init(&uma_pcpu_mtx[(cpu)], "UMA pcpu", "UMA pcpu",  \
  347             MTX_DEF | MTX_DUPOK)
  348 
  349 #define CPU_LOCK(cpu)                                           \
  350         mtx_lock(&uma_pcpu_mtx[(cpu)])
  351 
  352 #define CPU_UNLOCK(cpu)                                         \
  353         mtx_unlock(&uma_pcpu_mtx[(cpu)])
  354 
  355 /*
  356  * Find a slab within a hash table.  This is used for OFFPAGE zones to lookup
  357  * the slab structure.
  358  *
  359  * Arguments:
  360  *      hash  The hash table to search.
  361  *      data  The base page of the item.
  362  *
  363  * Returns:
  364  *      A pointer to a slab if successful, else NULL.
  365  */
  366 static __inline uma_slab_t
  367 hash_sfind(struct uma_hash *hash, u_int8_t *data)
  368 {
  369         uma_slab_t slab;
  370         int hval;
  371 
  372         hval = UMA_HASH(hash, data);
  373 
  374         SLIST_FOREACH(slab, &hash->uh_slab_hash[hval], us_hlink) {
  375                 if ((u_int8_t *)slab->us_data == data)
  376                         return (slab);
  377         }
  378         return (NULL);
  379 }
  380 
  381 static __inline uma_slab_t
  382 vtoslab(vm_offset_t va)
  383 {
  384         vm_page_t p;
  385         uma_slab_t slab;
  386 
  387         p = PHYS_TO_VM_PAGE(pmap_kextract(va));
  388         slab = (uma_slab_t )p->object;
  389 
  390         if (p->flags & PG_SLAB)
  391                 return (slab);
  392         else
  393                 return (NULL);
  394 }
  395 
  396 static __inline void
  397 vsetslab(vm_offset_t va, uma_slab_t slab)
  398 {
  399         vm_page_t p;
  400 
  401         p = PHYS_TO_VM_PAGE(pmap_kextract(va));
  402         p->object = (vm_object_t)slab;
  403         p->flags |= PG_SLAB;
  404 }
  405 
  406 static __inline void
  407 vsetobj(vm_offset_t va, vm_object_t obj)
  408 {
  409         vm_page_t p;
  410 
  411         p = PHYS_TO_VM_PAGE(pmap_kextract(va));
  412         p->object = obj;
  413         p->flags &= ~PG_SLAB;
  414 }
  415 
  416 /*
  417  * The following two functions may be defined by architecture specific code
  418  * if they can provide more effecient allocation functions.  This is useful
  419  * for using direct mapped addresses.
  420  */
  421 void *uma_small_alloc(uma_zone_t zone, int bytes, u_int8_t *pflag, int wait);
  422 void uma_small_free(void *mem, int size, u_int8_t flags);
  423 
  424 #endif /* VM_UMA_INT_H */

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