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

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Message-ID: <20170822212408.GC28715@tassilo.jf.intel.com>
Date:   Tue, 22 Aug 2017 14:24:08 -0700
From:   Andi Kleen <ak@...ux.intel.com>
To:     Christopher Lameter <cl@...ux.com>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        "Liang, Kan" <kan.liang@...el.com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Mel Gorman <mgorman@...e.de>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Ingo Molnar <mingo@...e.hu>,
        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 Tue, Aug 22, 2017 at 04:08:52PM -0500, Christopher Lameter wrote:
> On Tue, 22 Aug 2017, Andi Kleen wrote:
> 
> > We only see it on 4S+ today. But systems are always getting larger,
> > so what's a large system today, will be a normal medium scale system
> > tomorrow.
> >
> > BTW we also collected PT traces for the long hang cases, but it was
> > hard to find a consistent pattern in them.
> 
> Hmmm... Maybe it would be wise to limit the pages autonuma can migrate?
> 
> If a page has more than 50 refcounts or so then dont migrate it. I think
> high number of refcounts and a high frequewncy of calls are reached in
> particular for pages of the c library. Attempting to migrate those does
> not make much sense anyways because the load may shift and another
> function may become popular. We may end up shifting very difficult to
> migrate pages back and forth.

I believe in this case it's used by threads, so a reference count limit
wouldn't help.

If migrating code was a problem I would probably rather just disable
migration of read-only pages.

-Andi