Patch "NFS: Fix a performance regression in readdir" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

NFS: Fix a performance regression in readdir

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
nfs-fix-a-performance-regression-in-readdir.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Trond Myklebust <[email protected]>
Date: Sat, 19 Nov 2016 10:54:55 -0500
Subject: NFS: Fix a performance regression in readdir

From: Trond Myklebust <[email protected]>

commit 79f687a3de9e3ba2518b4ea33f38ca6cbe9133eb upstream.

Ben Coddington reports that commit 311324ad1713, by adding the function nfs_dir_mapping_need_revalidate() that checks page cache validity on each call to nfs_readdir() causes a performance regression when the directory is being modified.

If the directory is changing while we're iterating through the directory, POSIX does not require us to invalidate the page cache unless the user calls rewinddir(). However, we still do want to ensure that we use readdirplus in order to avoid a load of stat() calls when the user is doing an 'ls -l' workload.

The fix should be to invalidate the page cache immediately when we're setting the NFS_INO_ADVISE_RDPLUS bit.

---
 fs/nfs/dir.c |   15 ++-------------
 1 file changed, 2 insertions(+), 13 deletions(-)

@@ -477,7 +477,7 @@ void nfs_force_use_readdirplus(struct in
 {
 	if (!list_empty(&NFS_I(dir)->open_files)) {
 		nfs_advise_use_readdirplus(dir);
-		nfs_zap_mapping(dir, dir->i_mapping);
+		invalidate_mapping_pages(dir->i_mapping, 0, -1);
 	}
 }
 

@@ -886,17 +886,6 @@ int uncached_readdir(nfs_readdir_descrip
 	goto out;
 }
 
-static bool nfs_dir_mapping_need_revalidate(struct inode *dir)
-{
-	struct nfs_inode *nfsi = NFS_I(dir);
-
-	if (nfs_attribute_cache_expired(dir))
-		return true;
-	if (nfsi->cache_validity & NFS_INO_INVALID_DATA)
-		return true;
-	return false;
-}
-
 /* The file offset position represents the dirent entry number.  A
    last cookie cache takes care of the common case of reading the
    whole directory.

@@ -928,7 +917,7 @@ static int nfs_readdir(struct file *file
 	desc->decode = NFS_PROTO(inode)->decode_dirent;
 	desc->plus = nfs_use_readdirplus(inode, ctx) ? 1 : 0;
 
-	if (ctx->pos == 0 || nfs_dir_mapping_need_revalidate(inode))
+	if (ctx->pos == 0 || nfs_attribute_cache_expired(inode))
 		res = nfs_revalidate_mapping(inode, file->f_mapping);
 	if (res < 0)
 		goto out;

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/pnfs-fix-race-in-pnfs_wait_on_layoutreturn.patch queue-4.9/nfs-fix-typo-in-parameter-description.patch queue-4.9/nfs-fix-a-performance-regression-in-readdir.patch queue-4.9/nfsv4.1-nfs4_fl_prepare_ds-must-be-careful-about-reporting-success.patch