linux-kernel - Re: [PATCH 2/3] mm, compaction: split off flag for not updating skip hints

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Date:   Thu, 2 Nov 2017 13:09:43 +0000
From:   Mel Gorman <mgorman@...hsingularity.net>
To:     Vlastimil Babka <vbabka@...e.cz>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>
Subject: Re: [PATCH 2/3] mm, compaction: split off flag for not updating skip
 hints

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 <vbabka@...e.cz>

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

-- 
Mel Gorman
SUSE Labs