linux-kernel - Re: Is it safe for kthreadd to drain_all

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Message-ID: <alpine.LSU.2.11.1704070952530.2261@eggly.anvils>
Date:   Fri, 7 Apr 2017 09:58:17 -0700 (PDT)
From:   Hugh Dickins <hughd@...gle.com>
To:     Michal Hocko <mhocko@...nel.org>
cc:     Hugh Dickins <hughd@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Tejun Heo <tj@...nel.org>, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org
Subject: Re: Is it safe for kthreadd to drain_all_pages?

On Fri, 7 Apr 2017, Michal Hocko wrote:
> On Fri 07-04-17 09:25:33, Hugh Dickins wrote:
> [...]
> > 24 hours so far, and with a clean /var/log/messages.  Not conclusive
> > yet, and of course I'll leave it running another couple of days, but
> > I'm increasingly sure that it works as you intended: I agree that
> > 
> > mm-move-pcp-and-lru-pcp-drainging-into-single-wq.patch
> > mm-move-pcp-and-lru-pcp-drainging-into-single-wq-fix.patch
> > 
> > should go to Linus as soon as convenient.  Though I think the commit
> > message needs something a bit stronger than "Quite annoying though".
> > Maybe add a line:
> > 
> > Fixes serious hang under load, observed repeatedly on 4.11-rc.
> 
> Yeah, it is much less theoretical now. I will rephrase and ask Andrew to
> update the chagelog and send it to Linus once I've got your final go.

I don't know akpm's timetable, but your fix being more than a two-liner,
I think it would be better if it could get into rc6, than wait another
week for rc7, just in case others then find problems with it.  So I
think it's safer *not* to wait for my final go, but proceed on the
assumption that it will follow a day later.

Hugh