From: Oleg Nesterov <oleg@redhat.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Hugh Dickins <hughd@google.com>, Michal Hocko <mhocko@kernel.org>,
Linux-MM <linux-mm@kvack.org>,
LKML <linux-kernel@vger.kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
Tim Chen <tim.c.chen@linux.intel.com>,
Michal Hocko <mhocko@suse.com>
Subject: Re: [RFC PATCH] mm: silence soft lockups from unlock_page
Date: Sun, 26 Jul 2020 15:57:05 +0200 [thread overview]
Message-ID: <20200726135705.GA14017@redhat.com> (raw)
In-Reply-To: <CAHk-=wgpdbxaWWxOeVeA-eTex6QcSZLK9S2=eSv6KbQdPapfug@mail.gmail.com>
Linus,
I was greatly confused and tried to confuse you.
Somehow I misunderstood your last version and didn't bother to read it
again until now.
Sorry for noise and thanks for your explanations.
Oleg.
On 07/25, Linus Torvalds wrote:
>
> On Sat, Jul 25, 2020 at 12:28 PM Oleg Nesterov <oleg@redhat.com> wrote:
> >
> > What I tried to say. AFAICS before that commit we had (almost) the same
> > behaviour you propose now: unlock_page/etc wakes all the non-exclusive
> > waiters up.
> >
> > No?
>
> Yes, but no.
>
> We'd wake them _up_ fairly aggressively, but then they'd be caught on
> the bit being set again by the exclusive locker (that we also woke
> up).
>
> So they'd get woken up, and then go to sleep again.
>
> So the new behavior wakes things up more aggressively (but a different
> way), but not by letting them go out of order and early, but simply by
> not going back to sleep again.
>
> So the "wake up more" is very different - now it's about not going to
> sleep again, rather than by ordering the wakeup queue.
>
> We _could_ order the wakeup queue too, and put all non-exclusive
> weiters at the head again. And make it *really* aggressive.
>
> But since one of ourissues has been "latency of walking the wait
> queue", I'm not sure we want that. interspesing any blocking waiters -
> and stopping the waitqueue walking as a result - might be better under
> load.
>
> Wild handwaving. We could try it, but IO think that really would be a
> separate "try this out" patch.
>
> Right now, I think my patch will likely make for _better_ latencies
> for everything.
>
> Lower latency of non-exclusive waiters (because not going back to
> sleep), but also lower latency of walking the wait queue (because
> fewer entries, hopefully, and also less contention due to the "not
> going back to sleep" noise)
>
> Linus
>
next prev parent reply other threads:[~2020-07-26 13:57 UTC|newest]
Thread overview: 54+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-21 6:32 [RFC PATCH] mm: silence soft lockups from unlock_page Michal Hocko
[not found] ` <FCC3EB2D-9F11-4E9E-88F4-40B2926B35CC@lca.pw>
2020-07-21 11:25 ` Michal Hocko
[not found] ` <664A07B6-DBCD-4520-84F1-241A4E7A339F@lca.pw>
2020-07-21 12:17 ` Michal Hocko
[not found] ` <20200721132343.GA4261@lca.pw>
2020-07-21 13:38 ` Michal Hocko
2020-07-21 14:17 ` Chris Down
2020-07-21 15:00 ` Michal Hocko
2020-07-21 15:33 ` Linus Torvalds
2020-07-21 15:49 ` Michal Hocko
2020-07-22 18:29 ` Linus Torvalds
2020-07-22 21:29 ` Hugh Dickins
2020-07-22 22:10 ` Linus Torvalds
2020-07-22 23:42 ` Linus Torvalds
2020-07-23 0:23 ` Linus Torvalds
2020-07-23 12:47 ` Oleg Nesterov
2020-07-23 17:32 ` Linus Torvalds
2020-07-23 18:01 ` Oleg Nesterov
2020-07-23 18:22 ` Linus Torvalds
2020-07-23 19:03 ` Linus Torvalds
2020-07-24 14:45 ` Oleg Nesterov
2020-07-23 20:03 ` Linus Torvalds
2020-07-23 23:11 ` Hugh Dickins
2020-07-23 23:43 ` Linus Torvalds
2020-07-24 0:07 ` Hugh Dickins
2020-07-24 0:46 ` Linus Torvalds
2020-07-24 3:45 ` Hugh Dickins
2020-07-24 15:24 ` Oleg Nesterov
2020-07-24 17:32 ` Linus Torvalds
2020-07-24 23:25 ` Linus Torvalds
2020-07-25 2:08 ` Hugh Dickins
2020-07-25 2:46 ` Linus Torvalds
2020-07-25 10:14 ` Oleg Nesterov
2020-07-25 18:48 ` Linus Torvalds
2020-07-25 19:27 ` Oleg Nesterov
2020-07-25 19:51 ` Linus Torvalds
2020-07-26 13:57 ` Oleg Nesterov [this message]
2020-07-25 21:19 ` Hugh Dickins
2020-07-26 4:22 ` Hugh Dickins
2020-07-26 20:30 ` Hugh Dickins
2020-07-26 20:41 ` Linus Torvalds
2020-07-26 22:09 ` Hugh Dickins
2020-07-27 19:35 ` Greg KH
2020-08-06 5:46 ` Hugh Dickins
2020-08-18 13:50 ` Greg KH
2020-08-06 5:21 ` Hugh Dickins
2020-08-06 17:07 ` Linus Torvalds
2020-08-06 18:00 ` Matthew Wilcox
2020-08-06 18:32 ` Linus Torvalds
2020-08-07 18:41 ` Hugh Dickins
2020-08-07 19:07 ` Linus Torvalds
2020-08-07 19:35 ` Matthew Wilcox
2020-08-03 13:14 ` Michal Hocko
2020-08-03 17:56 ` Linus Torvalds
2020-07-25 9:39 ` Oleg Nesterov
2020-07-23 8:03 ` Michal Hocko
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