linux-kernel - Re: [PATCH v17 7/9] mm/page_reporting: Rotate reported pages to the tail of the list

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Date:   Wed, 19 Feb 2020 14:59:08 +0000
From:   Mel Gorman <mgorman@...hsingularity.net>
To:     Alexander Duyck <alexander.duyck@...il.com>
Cc:     kvm@...r.kernel.org, david@...hat.com, mst@...hat.com,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        akpm@...ux-foundation.org, yang.zhang.wz@...il.com,
        pagupta@...hat.com, konrad.wilk@...cle.com, nitesh@...hat.com,
        riel@...riel.com, willy@...radead.org, lcapitulino@...hat.com,
        dave.hansen@...el.com, wei.w.wang@...el.com, aarcange@...hat.com,
        pbonzini@...hat.com, dan.j.williams@...el.com, mhocko@...nel.org,
        alexander.h.duyck@...ux.intel.com, vbabka@...e.cz,
        osalvador@...e.de
Subject: Re: [PATCH v17 7/9] mm/page_reporting: Rotate reported pages to the
 tail of the list

On Tue, Feb 11, 2020 at 02:47:08PM -0800, Alexander Duyck wrote:
> From: Alexander Duyck <alexander.h.duyck@...ux.intel.com>
> 
> Rather than walking over the same pages again and again to get to the pages
> that have yet to be reported we can save ourselves a significant amount of
> time by simply rotating the list so that when we have a full list of
> reported pages the head of the list is pointing to the next non-reported
> page. Doing this should save us some significant time when processing each
> free list.
> 
> This doesn't gain us much in the standard case as all of the non-reported
> pages should be near the top of the list already. However in the case of
> page shuffling this results in a noticeable improvement. Below are the
> will-it-scale page_fault1 w/ THP numbers for 16 tasks with and without
> this patch.
> 
> Without:
> tasks   processes       processes_idle  threads         threads_idle
> 16      8093776.25      0.17            5393242.00      38.20
> 
> With:
> tasks   processes       processes_idle  threads         threads_idle
> 16      8283274.75      0.17            5594261.00      38.15
> 
> Signed-off-by: Alexander Duyck <alexander.h.duyck@...ux.intel.com>

Thanks for pulling this patch out and noting its impact. I think the
rotation is ok and if it turns out I missed something, it'll be
relatively easy to back out just the optimisation and leave the rest of
the feature intact.

Acked-by: Mel Gorman <mgorman@...hsingularity.net>

-- 
Mel Gorman
SUSE Labs