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

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Date:   Sat, 8 Apr 2017 10:04:20 -0700 (PDT)
From:   Hugh Dickins <hughd@...gle.com>
To:     Hugh Dickins <hughd@...gle.com>
cc:     Michal Hocko <mhocko@...nel.org>,
        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, Hugh Dickins wrote:
> On Fri, 7 Apr 2017, Michal Hocko wrote:
> > On Fri 07-04-17 09:58:17, Hugh Dickins wrote:
> > > 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.
> > 
> > Fair enough. Andrew, could you update the changelog of
> > mm-move-pcp-and-lru-pcp-drainging-into-single-wq.patch
> > and send it to Linus along with
> > mm-move-pcp-and-lru-pcp-drainging-into-single-wq-fix.patch before rc6?
> > 
> > I would add your Teste-by Hugh but I guess you want to give your testing
> > more time before feeling comfortable to give it.
> 
> Yes, fair enough: at the moment it's just
> Half-Tested-by: Hugh Dickins <hughd@...gle.com>
> and I hope to take the Half- off in about 21 hours.
> But I certainly wouldn't mind if it found its way to Linus without my
> final seal of approval.

48 hours and still going well: I declare it good, and thanks to Andrew,
Linus has ce612879ddc7 "mm: move pcp and lru-pcp draining into single wq"
already in for rc6.

Hugh