NFS: Reduce lock contention in nfs_page_find_head_request()

Add a lockless check for whether or not the page might be carrying
an existing writeback before we grab the inode->i_lock.

Reported-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>

diff --git a/fs/nfs/write.c b/fs/nfs/write.c
index 1d447e37f472be2d17395e4aea98a276c629e673..06e150c4e31513ce72d7f66a432c7e2a699d0880 100644 (file)
--- a/fs/nfs/write.c
+++ b/fs/nfs/write.c
@@ -190,9 +190,11 @@ static struct nfs_page *nfs_page_find_head_request(struct page *page)
        struct inode *inode = page_file_mapping(page)->host;
        struct nfs_page *req = NULL;
 
-       spin_lock(&inode->i_lock);
-       req = nfs_page_find_head_request_locked(NFS_I(inode), page);
-       spin_unlock(&inode->i_lock);
+       if (PagePrivate(page) || PageSwapCache(page)) {
+               spin_lock(&inode->i_lock);
+               req = nfs_page_find_head_request_locked(NFS_I(inode), page);
+               spin_unlock(&inode->i_lock);
+       }
        return req;
 }