[patch] fs/nfs: Add a resched point to nfs_commit_release_pages()

[Mike Galbraith <efault@gmx.de>]

On Mon, 2017-12-18 at 17:24 +0000, Trond Myklebust wrote:
> On Mon, 2017-12-18 at 18:00 +0100, Mike Galbraith wrote:
> > On Mon, 2017-12-18 at 11:35 -0500, J. Bruce Fields wrote:
> > > 
> > > Like I say, I don't really understand the issues here, so it's more
> > > a
> > > question than an objection....  (I don't know any reason a
> > > cond_resched() would be bad there.)
> > 
> > Think of it this way: what all can be queued up behind that kworker
> > that is hogging CPU for huge swaths of time?  It's not only userspace
> > that suffers.
> > 
> 
> Any cond_sched() belongs in the loop in nfs_commit_release_pages()
> (where it can be mitigated) rather than in a function whose purpose is
> to free memory. There is no reason to call it from the writeback or
> readpages code.

Just in case NFS folks are expecting a patchlet, trash otherwise.

fs/nfs: Add a resched point to nfs_commit_release_pages()

During heavy NFS write, kworkers can do very large amounts of work
without scheduling (82ms traced).  Add a resched point.

Signed-off-by: Mike Galbraith <efault@gmx.de>
Suggested-by: Trond Myklebust <trondmy@primarydata.com>
---
 fs/nfs/write.c |    1 +
 1 file changed, 1 insertion(+)

--- a/fs/nfs/write.c
+++ b/fs/nfs/write.c
@@ -1837,6 +1837,7 @@ static void nfs_commit_release_pages(str
 		set_bit(NFS_CONTEXT_RESEND_WRITES, &req->wb_context->flags);
 	next:
 		nfs_unlock_and_release_request(req);
+		cond_resched();
 	}
 	nfss = NFS_SERVER(data->inode);
 	if (atomic_long_read(&nfss->writeback) < NFS_CONGESTION_OFF_THRESH)