linux-kernel - Re: [PATCH 1/5] mm, page_alloc: Spread allocations across zones before introducing fragmentation

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Date:   Mon, 26 Nov 2018 13:36:57 +0100
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Mel Gorman <mgorman@...hsingularity.net>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     David Rientjes <rientjes@...gle.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Zi Yan <zi.yan@...rutgers.edu>,
        Michal Hocko <mhocko@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>
Subject: Re: [PATCH 1/5] mm, page_alloc: Spread allocations across zones
 before introducing fragmentation

On 11/23/18 12:45 PM, Mel Gorman wrote:
...


> Fault latencies are slightly reduced while allocation success rates remain
> at zero as this configuration does not make any special effort to allocate
> THP and fio is heavily active at the time and either filling memory or
> keeping pages resident. However, a 49% reduction of serious fragmentation
> events reduces the changes of external fragmentation being a problem in
> the future.
> 
> Vlastimil asked during review for a breakdown of the allocation types
> that are falling back.
> 
> vanilla
>    3816 MIGRATE_UNMOVABLE
>  800845 MIGRATE_MOVABLE
>      33 MIGRATE_UNRECLAIMABLE
> 
> patch
>     735 MIGRATE_UNMOVABLE
>  408135 MIGRATE_MOVABLE
>      42 MIGRATE_UNRECLAIMABLE

Nit: it's MIGRATE_RECLAIMABLE :)

> The majority of the fallbacks are due to movable allocations and this is
> consistent for the workload throughout the series so will not be presented
> again as the primary source of fallbacks are movable allocations.

Note that I was more interested in the *reduction* of different kinds of
fallbacks, not their ratios - that the majority is caused by movable
allocations is fully expected.
And the results above actually show that while the reduction for MOVABLE
is ~50%, the reduction for UNMOVABLE is actually 80%! IMHO that's great
(better than I would expect, in fact), and good to know.

...

> Overall, the patch reduces the number of external fragmentation causing
> events so the success of THP over long periods of time would be improved
> for this adverse workload.
> 
> Signed-off-by: Mel Gorman <mgorman@...hsingularity.net>

Acked-by: Vlastimil Babka <vbabka@...e.cz>