NFS: avoid waiting at all in nfs_release_page when congested.
authorNeilBrown <neilb@suse.de>
Wed, 24 Sep 2014 01:28:32 +0000 (11:28 +1000)
committerTrond Myklebust <trond.myklebust@primarydata.com>
Thu, 25 Sep 2014 12:25:38 +0000 (08:25 -0400)
commit353db7966288a2f18da22438aeec2b4862c0b241
tree959b0fe5a246747af6db55bb7652d4d35b738ba8
parent9590544694becc64f4874963dbfc4b4d391024b7
NFS: avoid waiting at all in nfs_release_page when congested.

If nfs_release_page() is called on a sequence of pages which are all
in the same file which is blocked on COMMIT, each page could
contribute a 1 second delay which could be come excessive.  I have
seen delays of as much as 208 seconds.

To keep the delay to one second, mark the bdi as write-congested
if the commit didn't finished.  Once it does finish, the
write-congested flag will be cleared by nfs_commit_release_pages().

With this, the longest total delay in try_to_free_pages that I have
seen is under 3 seconds.  With no waiting in nfs_release_page at all
I have seen delays of nearly 1.5 seconds.

Signed-off-by: NeilBrown <neilb@suse.de>
Acked-by: Jeff Layton <jlayton@primarydata.com>
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>
fs/nfs/file.c
fs/nfs/write.c