linux-kernel - RE: [PATCH 1/2] sched/wait: Break up long wake list walk

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Date:   Wed, 23 Aug 2017 20:55:15 +0000
From:   "Liang, Kan" <kan.liang@...el.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Tim Chen <tim.c.chen@...ux.intel.com>
CC:     Mel Gorman <mgorman@...hsingularity.net>,
        Mel Gorman <mgorman@...e.de>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...e.hu>, Andi Kleen <ak@...ux.intel.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Johannes Weiner" <hannes@...xchg.org>, Jan Kara <jack@...e.cz>,
        linux-mm <linux-mm@...ck.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH 1/2] sched/wait: Break up long wake list walk

> 
> On Wed, Aug 23, 2017 at 8:58 AM, Tim Chen <tim.c.chen@...ux.intel.com>
> wrote:
> >
> > Will you still consider the original patch as a fail safe mechanism?
> 
> I don't think we have much choice, although I would *really* want to get this
> root-caused rather than just papering over the symptoms.
> 
> Maybe still worth testing that "sched/numa: Scale scan period with tasks in
> group and shared/private" patch that Mel mentioned.

The patch doesn’t help on our load.

Thanks,
Kan
> 
> In fact, looking at that patch description, it does seem to match this particular
> load a lot. Quoting from the commit message:
> 
>   "Running 80 tasks in the same group, or as threads of the same process,
>    results in the memory getting scanned 80x as fast as it would be if a
>    single task was using the memory.
> 
>    This really hurts some workloads"
> 
> So if 80 threads causes 80x as much scanning, a few thousand threads might
> indeed be really really bad.
> 
> So once more unto the breach, dear friends, once more.
> 
> Please.
> 
> The patch got applied to -tip as commit b5dd77c8bdad, and can be
> downloaded here:
> 
> 
> https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git/commit/?id=b5dd
> 77c8bdada7b6262d0cba02a6ed525bf4e6e1
> 
> (Hmm. It says it's cc'd to me, but I never noticed that patch simply because it
> was in a big group of other -tip commits.. Oh well).
> 
>           Linus