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Subject: Re: [PATCH 05/11] mm, compaction: distinguish COMPACT_DEFERRED from
 COMPACT_SKIPPED
To: Michal Hocko <mhocko@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>
References: <1459855533-4600-1-git-send-email-mhocko@kernel.org>
 <1459855533-4600-6-git-send-email-mhocko@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
        Johannes Weiner <hannes@cmpxchg.org>, Mel Gorman <mgorman@suse.de>,
        David Rientjes <rientjes@google.com>,
        Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>,
        Joonsoo Kim <js1304@gmail.com>,
        Hillf Danton <hillf.zj@alibaba-inc.com>, linux-mm@kvack.org,
        LKML <linux-kernel@vger.kernel.org>, Michal Hocko <mhocko@suse.com>
From: Vlastimil Babka <vbabka@suse.cz>
Message-ID: <570B843C.8050608@suse.cz>
Date: Mon, 11 Apr 2016 13:02:20 +0200
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On 04/05/2016 01:25 PM, Michal Hocko wrote:
> From: Michal Hocko <mhocko@suse.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@suse.com>

Patch itself is OK.

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