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Date:   Thu, 2 Nov 2017 13:09:43 +0000
From:   Mel Gorman <>
To:     Vlastimil Babka <>
Cc:     Andrew Morton <>,,, David Rientjes <>,
        Joonsoo Kim <>
Subject: Re: [PATCH 2/3] mm, compaction: split off flag for not updating skip

On Thu, Nov 02, 2017 at 01:17:05PM +0100, Vlastimil Babka wrote:
> Pageblock skip hints were added as a heuristic for compaction, which shares
> core code with CMA. Since CMA reliability would suffer from the heuristics,
> compact_control flag ignore_skip_hint was added for the CMA use case.
> Since commit 6815bf3f233e ("mm/compaction: respect ignore_skip_hint in
> update_pageblock_skip") the flag also means that CMA won't *update* the skip
> hints in addition to ignoring them.
> Today, direct compaction can also ignore the skip hints in the last resort
> attempt, but there's no reason not to set them when isolation fails in such
> case. Thus, this patch splits off a new no_set_skip_hint flag to avoid the
> updating, which only CMA sets. This should improve the heuristics a bit, and
> allow us to simplify the persistent skip bit handling as the next step.
> Signed-off-by: Vlastimil Babka <>

Acked-by: Mel Gorman <>

Mel Gorman

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