NFS: Add an ACCESS cache memory shrinker

A pinned inode may in theory end up filling memory with cached ACCESS
calls. This patch ensures that the VM may shrink away the cache in these
particular cases.
The shrinker works by iterating through the list of inodes on the global
nfs_access_lru_list, and removing the least recently used access
cache entry until it is done (or until the entire cache is empty).

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

1 files changed, 44 insertions, 0 deletions

diff --git a/fs/nfs/dir.c b/fs/nfs/dir.c
index bf4f5ffda703..067d144d141b 100644
--- a/fs/nfs/dir.c
+++ b/fs/nfs/dir.c
@@ -1651,6 +1651,50 @@ static void nfs_access_free_entry(struct nfs_access_entry *entry)
         smp_mb__after_atomic_dec();
 }
 
+int nfs_access_cache_shrinker(int nr_to_scan, gfp_t gfp_mask)
+{
+        LIST_HEAD(head);
+        struct nfs_inode *nfsi;
+        struct nfs_access_entry *cache;
+
+        spin_lock(&nfs_access_lru_lock);
+restart:
+        list_for_each_entry(nfsi, &nfs_access_lru_list, access_cache_inode_lru) {
+                struct inode *inode;
+
+                if (nr_to_scan-- == 0)
+                        break;
+                inode = igrab(&nfsi->vfs_inode);
+                if (inode == NULL)
+                        continue;
+                spin_lock(&inode->i_lock);
+                if (list_empty(&nfsi->access_cache_entry_lru))
+                        goto remove_lru_entry;
+                cache = list_entry(nfsi->access_cache_entry_lru.next,
+                                struct nfs_access_entry, lru);
+                list_move(&cache->lru, &head);
+                rb_erase(&cache->rb_node, &nfsi->access_cache);
+                if (!list_empty(&nfsi->access_cache_entry_lru))
+                        list_move_tail(&nfsi->access_cache_inode_lru,
+                                        &nfs_access_lru_list);
+                else {
+remove_lru_entry:
+                        list_del_init(&nfsi->access_cache_inode_lru);
+                        clear_bit(NFS_INO_ACL_LRU_SET, &nfsi->flags);
+                }
+                spin_unlock(&inode->i_lock);
+                iput(inode);
+                goto restart;
+        }
+        spin_unlock(&nfs_access_lru_lock);
+        while (!list_empty(&head)) {
+                cache = list_entry(head.next, struct nfs_access_entry, lru);
+                list_del(&cache->lru);
+                nfs_access_free_entry(cache);
+        }
+        return (atomic_long_read(&nfs_access_nr_entries) / 100) * sysctl_vfs_cache_pressure;
+}
+
 static void __nfs_access_zap_cache(struct inode *inode)
 {
         struct nfs_inode *nfsi = NFS_I(inode);