Date: Thu, 19 Aug 2010 10:15:25 -0400
From: Jeff Layton <jlayton@redhat.com>
To: linux-nfs@vger.kernel.org
Subject: why are WB_SYNC_NONE COMMITs being done with FLUSH_SYNC set ?
Message-ID: <20100819101525.076831ad@barsoom.rdu.redhat.com>
Content-Type: text/plain; charset=US-ASCII
Sender: linux-nfs-owner@vger.kernel.org
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I'm looking at backporting some upstream changes to earlier kernels,
and ran across something I don't quite understand...

In nfs_commit_unstable_pages, we set the flags to FLUSH_SYNC. We then
zero out the flags if wbc->nonblocking or wbc->for_background is set.

Shouldn't we also clear it out if wbc->sync_mode == WB_SYNC_NONE ?
WB_SYNC_NONE means "don't wait on anything", so shouldn't that include
not waiting on the COMMIT to complete?

For discussion purposes, here's a patch that shows what I'm talking
about (completely untested):

diff --git a/fs/nfs/write.c b/fs/nfs/write.c
index 874972d..2fca906 100644
--- a/fs/nfs/write.c
+++ b/fs/nfs/write.c
@@ -1440,7 +1440,8 @@ static int nfs_commit_unstable_pages(struct inode *inode, struct writeback_contr
 	    nfsi->ncommit <= (nfsi->npages >> 1))
 		goto out_mark_dirty;
 
-	if (wbc->nonblocking || wbc->for_background)
+	if (wbc->nonblocking || wbc->for_background ||
+	    wbc->sync_mode == WB_SYNC_NONE)
 		flags = 0;
 	ret = nfs_commit_inode(inode, flags);
 	if (ret >= 0) {

-- 
Jeff Layton <jlayton@redhat.com>