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, 08 Jan 2020 08:07:52 -0800
From:   Alexander Duyck <alexander.h.duyck@...ux.intel.com>
To:     David Hildenbrand <david@...hat.com>,
        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, 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 Wed, 2020-01-08 at 14:38 +0100, David Hildenbrand wrote:
> 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.
> 

Okay, I will update if needed for the next version.