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

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Message-ID: <37D7C6CF3E00A74B8858931C1DB2F07753787AE4@SHSMSX103.ccr.corp.intel.com>
Date:   Fri, 18 Aug 2017 16:53:30 +0000
From:   "Liang, Kan" <kan.liang@...el.com>
To:     Mel Gorman <mgorman@...hsingularity.net>
CC:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Mel Gorman <mgorman@...e.de>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Tim Chen <tim.c.chen@...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 Fri, Aug 18, 2017 at 02:20:38PM +0000, Liang, Kan wrote:
> > > Nothing fancy other than needing a comment if it works.
> > >
> >
> > No, the patch doesn't work.
> >
> 
> That indicates that it may be a hot page and it's possible that the page is
> locked for a short time but waiters accumulate.  What happens if you leave
> NUMA balancing enabled but disable THP?  

No, disabling THP doesn't help the case.

Thanks,
Kan

> Waiting on migration entries also
> uses wait_on_page_locked so it would be interesting to know if the problem
> is specific to THP.
> 
> Can you tell me what this workload is doing? I want to see if it's something
> like many threads pounding on a limited number of pages very quickly. If it's
> many threads working on private data, it would also be important to know
> how each buffers threads are aligned, particularly if the buffers are smaller
> than a THP or base page size. For example, if each thread is operating on a
> base page sized buffer then disabling THP would side-step the problem but
> THP would be false sharing between multiple threads.
> 
> 
> --
> Mel Gorman
> SUSE Labs