linux-kernel - Re: [PATCH v16 7/9] mm: Rotate free list so reported pages are moved to the tail of the list

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Date:   Wed, 8 Jan 2020 14:38:56 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Alexander Duyck <alexander.duyck@...il.com>, kvm@...r.kernel.org,
        mst@...hat.com, linux-kernel@...r.kernel.org, willy@...radead.org,
        mhocko@...nel.org, linux-mm@...ck.org, akpm@...ux-foundation.org,
        mgorman@...hsingularity.net, vbabka@...e.cz
Cc:     yang.zhang.wz@...il.com, nitesh@...hat.com, konrad.wilk@...cle.com,
        pagupta@...hat.com, riel@...riel.com, lcapitulino@...hat.com,
        dave.hansen@...el.com, wei.w.wang@...el.com, aarcange@...hat.com,
        pbonzini@...hat.com, dan.j.williams@...el.com,
        alexander.h.duyck@...ux.intel.com, osalvador@...e.de
Subject: Re: [PATCH v16 7/9] mm: Rotate free list so reported pages are moved
 to the tail of the list

On 03.01.20 22:16, 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>
> ---
>  mm/page_reporting.c |   30 ++++++++++++++++++++++--------
>  1 file changed, 22 insertions(+), 8 deletions(-)

Just a minor comment while scanning over the patches (will do more
review soon), you might want to switch to "mm/page_reporting: " styled
subjects for these optimizations.

-- 
Thanks,

David / dhildenb