linux-kernel - Re: NFS: 82ms wakeup latency 4.14-rc4

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Message-ID: <1513617866.4581.6.camel@primarydata.com>
Date:   Mon, 18 Dec 2017 17:24:29 +0000
From:   Trond Myklebust <trondmy@...marydata.com>
To:     "bfields@...ldses.org" <bfields@...ldses.org>,
        "efault@....de" <efault@....de>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-nfs@...r.kernel.org" <linux-nfs@...r.kernel.org>,
        "jlayton@...nel.org" <jlayton@...nel.org>
Subject: Re: NFS: 82ms wakeup latency 4.14-rc4

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
trond.myklebust@...marydata.com