linux-kernel - Re: [PATCH 05/11] mm, compaction: distinguish COMPACT_DEFERRED from COMPACT

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Date:	Mon, 11 Apr 2016 13:02:20 +0200
From:	Vlastimil Babka <vbabka@...e.cz>
To:	Michal Hocko <mhocko@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Johannes Weiner <hannes@...xchg.org>,
	Mel Gorman <mgorman@...e.de>,
	David Rientjes <rientjes@...gle.com>,
	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
	Joonsoo Kim <js1304@...il.com>,
	Hillf Danton <hillf.zj@...baba-inc.com>, linux-mm@...ck.org,
	LKML <linux-kernel@...r.kernel.org>,
	Michal Hocko <mhocko@...e.com>
Subject: Re: [PATCH 05/11] mm, compaction: distinguish COMPACT_DEFERRED from
 COMPACT_SKIPPED

On 04/05/2016 01:25 PM, Michal Hocko wrote:
> From: Michal Hocko <mhocko@...e.com>
>
> try_to_compact_pages can currently return COMPACT_SKIPPED even when the
> compaction is defered for some zone just because zone DMA is skipped
> in 99% of cases due to watermark checks. This makes COMPACT_DEFERRED
> basically unusable for the page allocator as a feedback mechanism.
>
> Make sure we distinguish those two states properly and switch their
> ordering in the enum. This would mean that the COMPACT_SKIPPED will be
> returned only when all eligible zones are skipped.
>
> This shouldn't introduce any functional change.

Hmm, really? __alloc_pages_direct_compact() does distinguish 
COMPACT_DEFERRED, and sets *deferred compaction, so ultimately this is 
some change for THP allocations?

Also there's no mention of COMPACT_INACTIVE in the changelog (which 
indeed isn't functional change, but might surprise somebody).

> Signed-off-by: Michal Hocko <mhocko@...e.com>

Patch itself is OK.

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