Re: NFS: 82ms wakeup latency 4.14-rc4

From: Trond Myklebust
Date: Mon Dec 18 2017 - 12:24:46 EST

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.

Trond Myklebust
Linux NFS client maintainer, PrimaryData