FreeBSD/Linux Kernel Cross Reference
sys/fs/nfs/pagelist.c

     /*
      * linux/fs/nfs/pagelist.c
      *
      * A set of helper functions for managing NFS read and write requests.
      * The main purpose of these routines is to provide support for the
      * coalescing of several requests into a single RPC call.
      *
      * Copyright 2000, 2001 (c) Trond Myklebust <trond.myklebust@fys.uio.no>
      *
     */
    
    #include <linux/config.h>
    #include <linux/slab.h>
    #include <linux/file.h>
    #include <linux/sunrpc/clnt.h>
    #include <linux/nfs3.h>
    #include <linux/nfs_page.h>
    #include <linux/nfs_fs.h>
    #include <linux/nfs_flushd.h>
    #include <linux/nfs_mount.h>
    
    #define NFS_PARANOIA 1
    
    /*
     * Spinlock
     */
    spinlock_t nfs_wreq_lock = SPIN_LOCK_UNLOCKED;
    
    static kmem_cache_t *nfs_page_cachep;
    
    static inline struct nfs_page *
    nfs_page_alloc(void)
    {
            struct nfs_page *p;
            p = kmem_cache_alloc(nfs_page_cachep, SLAB_NOFS);
            if (p) {
                    memset(p, 0, sizeof(*p));
                    INIT_LIST_HEAD(&p->wb_hash);
                    INIT_LIST_HEAD(&p->wb_list);
                    INIT_LIST_HEAD(&p->wb_lru);
                    init_waitqueue_head(&p->wb_wait);
            }
            return p;
    }
    
    static inline void
    nfs_page_free(struct nfs_page *p)
    {
            kmem_cache_free(nfs_page_cachep, p);
    }
    
    static int nfs_try_to_free_pages(struct nfs_server *);
    
    /**
     * nfs_create_request - Create an NFS read/write request.
     * @cred: RPC credential to use
     * @inode: inode to which the request is attached
     * @page: page to write
     * @offset: starting offset within the page for the write
     * @count: number of bytes to read/write
     *
     * The page must be locked by the caller. This makes sure we never
     * create two different requests for the same page, and avoids
     * a possible deadlock when we reach the hard limit on the number
     * of dirty pages.
     * User should ensure it is safe to sleep in this function.
     */
    struct nfs_page *
    nfs_create_request(struct rpc_cred *cred, struct inode *inode,
                       struct page *page,
                       unsigned int offset, unsigned int count)
    {
            struct nfs_server *server = NFS_SERVER(inode);
            struct nfs_reqlist      *cache = NFS_REQUESTLIST(inode);
            struct nfs_page         *req;
    
            /* Deal with hard limits.  */
            for (;;) {
                    /* Prevent races by incrementing *before* we test */
                    atomic_inc(&cache->nr_requests);
    
                    /* If we haven't reached the local hard limit yet,
                     * try to allocate the request struct */
                    if (atomic_read(&cache->nr_requests) <= MAX_REQUEST_HARD) {
                            req = nfs_page_alloc();
                            if (req != NULL)
                                    break;
                    }
    
                    atomic_dec(&cache->nr_requests);
    
                    /* Try to free up at least one request in order to stay
                     * below the hard limit
                     */
                    if (nfs_try_to_free_pages(server))
                            continue;
                    if (signalled() && (server->flags & NFS_MOUNT_INTR))
                            return ERR_PTR(-ERESTARTSYS);
                    yield();
           }
   
           /* Initialize the request struct. Initially, we assume a
            * long write-back delay. This will be adjusted in
            * update_nfs_request below if the region is not locked. */
           req->wb_page    = page;
           page_cache_get(page);
           req->wb_offset  = offset;
           req->wb_bytes   = count;
   
           if (cred)
                   req->wb_cred = get_rpccred(cred);
           req->wb_inode   = inode;
           req->wb_count   = 1;
   
           return req;
   }
   
   /**
    * nfs_clear_request - Free up all resources allocated to the request
    * @req:
    *
    * Release all resources associated with a write request after it
    * has completed.
    */
   void nfs_clear_request(struct nfs_page *req)
   {
           /* Release struct file or cached credential */
           if (req->wb_file) {
                   fput(req->wb_file);
                   req->wb_file = NULL;
           }
           if (req->wb_cred) {
                   put_rpccred(req->wb_cred);
                   req->wb_cred = NULL;
           }
           if (req->wb_page) {
                   atomic_dec(&NFS_REQUESTLIST(req->wb_inode)->nr_requests);
   #ifdef NFS_PARANOIA
                   BUG_ON(atomic_read(&NFS_REQUESTLIST(req->wb_inode)->nr_requests) < 0);
   #endif
                   page_cache_release(req->wb_page);
                   req->wb_page = NULL;
           }
   }
   
   
   /**
    * nfs_release_request - Release the count on an NFS read/write request
    * @req: request to release
    *
    * Note: Should never be called with the spinlock held!
    */
   void
   nfs_release_request(struct nfs_page *req)
   {
           spin_lock(&nfs_wreq_lock);
           if (--req->wb_count) {
                   spin_unlock(&nfs_wreq_lock);
                   return;
           }
           __nfs_del_lru(req);
           spin_unlock(&nfs_wreq_lock);
   
   #ifdef NFS_PARANOIA
           BUG_ON(!list_empty(&req->wb_list));
           BUG_ON(!list_empty(&req->wb_hash));
           BUG_ON(NFS_WBACK_BUSY(req));
   #endif
   
           /* Release struct file or cached credential */
           nfs_clear_request(req);
           nfs_page_free(req);
   }
   
   /**
    * nfs_list_add_request - Insert a request into a sorted list
    * @req: request
    * @head: head of list into which to insert the request.
    *
    * Note that the wb_list is sorted by page index in order to facilitate
    * coalescing of requests.
    * We use an insertion sort that is optimized for the case of appended
    * writes.
    */
   void
   nfs_list_add_request(struct nfs_page *req, struct list_head *head)
   {
           struct list_head *pos;
           unsigned long pg_idx = page_index(req->wb_page);
   
   #ifdef NFS_PARANOIA
           if (!list_empty(&req->wb_list)) {
                   printk(KERN_ERR "NFS: Add to list failed!\n");
                   BUG();
           }
   #endif
           list_for_each_prev(pos, head) {
                   struct nfs_page *p = nfs_list_entry(pos);
                   if (page_index(p->wb_page) < pg_idx)
                           break;
           }
           list_add(&req->wb_list, pos);
           req->wb_list_head = head;
   }
   
   /**
    * nfs_wait_on_request - Wait for a request to complete.
    * @req: request to wait upon.
    *
    * Interruptible by signals only if mounted with intr flag.
    * The user is responsible for holding a count on the request.
    */
   int
   nfs_wait_on_request(struct nfs_page *req)
   {
           struct inode    *inode = req->wb_inode;
           struct rpc_clnt *clnt = NFS_CLIENT(inode);
   
           if (!NFS_WBACK_BUSY(req))
                   return 0;
           return nfs_wait_event(clnt, req->wb_wait, !NFS_WBACK_BUSY(req));
   }
   
   /**
    * nfs_coalesce_requests - Split coalesced requests out from a list.
    * @head: source list
    * @dst: destination list
    * @nmax: maximum number of requests to coalesce
    *
    * Moves a maximum of 'nmax' elements from one list to another.
    * The elements are checked to ensure that they form a contiguous set
    * of pages, and that they originated from the same file.
    */
   int
   nfs_coalesce_requests(struct list_head *head, struct list_head *dst,
                         unsigned int nmax)
   {
           struct nfs_page         *req = NULL;
           unsigned int            npages = 0;
   
           while (!list_empty(head)) {
                   struct nfs_page *prev = req;
   
                   req = nfs_list_entry(head->next);
                   if (prev) {
                           if (req->wb_cred != prev->wb_cred)
                                   break;
                           if (page_index(req->wb_page) != page_index(prev->wb_page)+1)
                                   break;
   
                           if (req->wb_offset != 0)
                                   break;
                   }
                   nfs_list_remove_request(req);
                   nfs_list_add_request(req, dst);
                   npages++;
                   if (req->wb_offset + req->wb_bytes != PAGE_CACHE_SIZE)
                           break;
                   if (npages >= nmax)
                           break;
           }
           return npages;
   }
   
   /*
    * nfs_scan_forward - Coalesce more requests
    * @req: First request to add
    * @dst: destination list
    * @nmax: maximum number of requests to coalesce
    *
    * Tries to coalesce more requests by traversing the request's wb_list.
    * Moves the resulting list into dst. Requests are guaranteed to be
    * contiguous, and to originate from the same file.
    */
   static int
   nfs_scan_forward(struct nfs_page *req, struct list_head *dst, int nmax)
   {
           struct nfs_server *server = NFS_SERVER(req->wb_inode);
           struct list_head *pos, *head = req->wb_list_head;
           struct rpc_cred *cred = req->wb_cred;
           unsigned long idx = page_index(req->wb_page) + 1;
           int npages = 0;
   
           for (pos = req->wb_list.next; nfs_lock_request(req); pos = pos->next) {
                   nfs_list_remove_request(req);
                   nfs_list_add_request(req, dst);
                   __nfs_del_lru(req);
                   __nfs_add_lru(&server->lru_busy, req);
                   npages++;
                   if (npages == nmax)
                           break;
                   if (pos == head)
                           break;
                   if (req->wb_offset + req->wb_bytes != PAGE_CACHE_SIZE)
                           break;
                   req = nfs_list_entry(pos);
                   if (page_index(req->wb_page) != idx++)
                           break;
                   if (req->wb_offset != 0)
                           break;
                   if (req->wb_cred != cred)
                           break;
           }
           return npages;
   }
   
   /**
    * nfs_scan_lru - Scan one of the least recently used list
    * @head: One of the NFS superblock lru lists
    * @dst: Destination list
    * @nmax: maximum number of requests to coalesce
    *
    * Scans one of the NFS superblock lru lists for upto nmax requests
    * and returns them on a list. The requests are all guaranteed to be
    * contiguous, originating from the same inode and the same file.
    */
   int
   nfs_scan_lru(struct list_head *head, struct list_head *dst, int nmax)
   {
           struct list_head *pos;
           struct nfs_page *req;
           int npages = 0;
   
           list_for_each(pos, head) {
                   req = nfs_lru_entry(pos);
                   npages = nfs_scan_forward(req, dst, nmax);
                   if (npages)
                           break;
           }
           return npages;
   }
   
   /**
    * nfs_scan_lru_timeout - Scan one of the superblock lru lists for timed out requests
    * @head: One of the NFS superblock lru lists
    * @dst: Destination list
    * @nmax: maximum number of requests to coalesce
    *
    * Scans one of the NFS superblock lru lists for upto nmax requests
    * and returns them on a list. The requests are all guaranteed to be
    * contiguous, originating from the same inode and the same file.
    * The first request on the destination list will be timed out, the
    * others are not guaranteed to be so.
    */
   int
   nfs_scan_lru_timeout(struct list_head *head, struct list_head *dst, int nmax)
   {
           struct list_head *pos;
           struct nfs_page *req;
           int npages = 0;
   
           list_for_each(pos, head) {
                   req = nfs_lru_entry(pos);
                   if (time_after(req->wb_timeout, jiffies))
                           break;
                   npages = nfs_scan_forward(req, dst, nmax);
                   if (npages)
                           break;
           }
           return npages;
   }
   
   /**
    * nfs_scan_list - Scan a list for matching requests
    * @head: One of the NFS inode request lists
    * @dst: Destination list
    * @file: if set, ensure we match requests from this file
    * @idx_start: lower bound of page->index to scan
    * @npages: idx_start + npages sets the upper bound to scan.
    *
    * Moves elements from one of the inode request lists.
    * If the number of requests is set to 0, the entire address_space
    * starting at index idx_start, is scanned.
    * The requests are *not* checked to ensure that they form a contiguous set.
    * You must be holding the nfs_wreq_lock when calling this function
    */
   int
   nfs_scan_list(struct list_head *head, struct list_head *dst,
                 struct file *file,
                 unsigned long idx_start, unsigned int npages)
   {
           struct list_head        *pos, *tmp;
           struct nfs_page         *req;
           unsigned long           idx_end;
           int                     res;
   
           res = 0;
           if (npages == 0)
                   idx_end = ~0;
           else
                   idx_end = idx_start + npages - 1;
   
           list_for_each_safe(pos, tmp, head) {
                   unsigned long pg_idx;
   
                   req = nfs_list_entry(pos);
   
                   if (file && req->wb_file != file)
                           continue;
   
                   pg_idx = page_index(req->wb_page);
                   if (pg_idx < idx_start)
                           continue;
                   if (pg_idx > idx_end)
                           break;
   
                   if (!nfs_lock_request(req))
                           continue;
                   nfs_list_remove_request(req);
                   nfs_list_add_request(req, dst);
                   __nfs_del_lru(req);
                   __nfs_add_lru(&NFS_SERVER(req->wb_inode)->lru_busy, req);
                   res++;
           }
           return res;
   }
   
   /*
    * nfs_try_to_free_pages - Free up NFS read/write requests
    * @server: The NFS superblock
    *
    * This function attempts to flush out NFS reads and writes in order
    * to keep the hard limit on the total number of pending requests
    * on a given NFS partition.
    * Note: we first try to commit unstable writes, then flush out pending
    *       reads, then finally the dirty pages.
    *       The assumption is that this reflects the ordering from the fastest
    *       to the slowest method for reclaiming requests.
    */
   static int
   nfs_try_to_free_pages(struct nfs_server *server)
   {
           LIST_HEAD(head);
           struct nfs_page *req = NULL;
           int nreq;
   
           for (;;) {
                   if (req) {
                           int status = nfs_wait_on_request(req);
                           nfs_release_request(req);
                           if (status)
                                   break;
                           req = NULL;
                   }
                   nreq = atomic_read(&server->rw_requests->nr_requests);
                   if (nreq < MAX_REQUEST_HARD)
                           return 1;
                   spin_lock(&nfs_wreq_lock);
                   /* Are there any busy RPC calls that might free up requests? */
                   if (!list_empty(&server->lru_busy)) {
                           req = nfs_lru_entry(server->lru_busy.next);
                           req->wb_count++;
                           __nfs_del_lru(req);
                           spin_unlock(&nfs_wreq_lock);
                           continue;
                   }
   
   #ifdef CONFIG_NFS_V3
                   /* Let's try to free up some completed NFSv3 unstable writes */
                   nfs_scan_lru_commit(server, &head);
                   if (!list_empty(&head)) {
                           spin_unlock(&nfs_wreq_lock);
                           nfs_commit_list(&head, 0);
                           continue;
                   }
   #endif
                   /* OK, so we try to free up some pending readaheads */
                   nfs_scan_lru_read(server, &head);
                   if (!list_empty(&head)) {
                           spin_unlock(&nfs_wreq_lock);
                           nfs_pagein_list(&head, server->rpages);
                           continue;
                   }
                   /* Last resort: we try to flush out single requests */
                   nfs_scan_lru_dirty(server, &head);
                   if (!list_empty(&head)) {
                           spin_unlock(&nfs_wreq_lock);
                           nfs_flush_list(&head, server->wpages, FLUSH_STABLE);
                           continue;
                   }
                   spin_unlock(&nfs_wreq_lock);
                   break;
           }
           /* We failed to free up requests */
           return 0;
   }
   
   int nfs_init_nfspagecache(void)
   {
           nfs_page_cachep = kmem_cache_create("nfs_page",
                                               sizeof(struct nfs_page),
                                               0, SLAB_HWCACHE_ALIGN,
                                               NULL, NULL);
           if (nfs_page_cachep == NULL)
                   return -ENOMEM;
   
           return 0;
   }
   
   void nfs_destroy_nfspagecache(void)
   {
           if (kmem_cache_destroy(nfs_page_cachep))
                   printk(KERN_INFO "nfs_page: not all structures were freed\n");
   }
   

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