NFS: Convert lookups of the lock context to RCU

Speed up lookups of an existing lock context by avoiding the inode->i_lock,
and using RCU instead.

Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>

1 files changed, 12 insertions, 13 deletions

diff --git a/fs/nfs/inode.c b/fs/nfs/inode.c
index b65aee481d13..09b3b7146ff4 100644
--- a/fs/nfs/inode.c
+++ b/fs/nfs/inode.c
@@ -857,15 +857,14 @@ static void nfs_init_lock_context(struct nfs_lock_context *l_ctx)
 
 static struct nfs_lock_context *__nfs_find_lock_context(struct nfs_open_context *ctx)
 {
-        struct nfs_lock_context *head = &ctx->lock_context;
-        struct nfs_lock_context *pos = head;
+        struct nfs_lock_context *pos;
 
-        do {
+        list_for_each_entry_rcu(pos, &ctx->lock_context.list, list) {
                 if (pos->lockowner != current->files)
                         continue;
-                refcount_inc(&pos->count);
-                return pos;
-        } while ((pos = list_entry(pos->list.next, typeof(*pos), list)) != head);
+                if (refcount_inc_not_zero(&pos->count))
+                        return pos;
+        }
         return NULL;
 }
 
@@ -874,10 +873,10 @@ struct nfs_lock_context *nfs_get_lock_context(struct nfs_open_context *ctx)
         struct nfs_lock_context *res, *new = NULL;
         struct inode *inode = d_inode(ctx->dentry);
 
-        spin_lock(&inode->i_lock);
+        rcu_read_lock();
         res = __nfs_find_lock_context(ctx);
+        rcu_read_unlock();
         if (res == NULL) {
-                spin_unlock(&inode->i_lock);
                 new = kmalloc(sizeof(*new), GFP_KERNEL);
                 if (new == NULL)
                         return ERR_PTR(-ENOMEM);
@@ -885,14 +884,14 @@ struct nfs_lock_context *nfs_get_lock_context(struct nfs_open_context *ctx)
                 spin_lock(&inode->i_lock);
                 res = __nfs_find_lock_context(ctx);
                 if (res == NULL) {
-                        list_add_tail(&new->list, &ctx->lock_context.list);
+                        list_add_tail_rcu(&new->list, &ctx->lock_context.list);
                         new->open_context = ctx;
                         res = new;
                         new = NULL;
                 }
+                spin_unlock(&inode->i_lock);
+                kfree(new);
         }
-        spin_unlock(&inode->i_lock);
-        kfree(new);
         return res;
 }
 EXPORT_SYMBOL_GPL(nfs_get_lock_context);
@@ -904,9 +903,9 @@ void nfs_put_lock_context(struct nfs_lock_context *l_ctx)
 
         if (!refcount_dec_and_lock(&l_ctx->count, &inode->i_lock))
                 return;
-        list_del(&l_ctx->list);
+        list_del_rcu(&l_ctx->list);
         spin_unlock(&inode->i_lock);
-        kfree(l_ctx);
+        kfree_rcu(l_ctx, rcu_head);
 }
 EXPORT_SYMBOL_GPL(nfs_put_lock_context);