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Date: Wed, 4 May 2016 23:39:14 +0900
Message-ID: <CAAmzW4MBC4tVJA1T3Py3ZwFmVPxE=X4+W6J5OQSp8aDu_YmboQ@mail.gmail.com>
Subject: Re: [PATCH 12/14] mm, oom: protect !costly allocations some more
From: Joonsoo Kim <js1304@gmail.com>
To: Michal Hocko <mhocko@kernel.org>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        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>,
        Hillf Danton <hillf.zj@alibaba-inc.com>,
        Vlastimil Babka <vbabka@suse.cz>,
        Linux Memory Management List <linux-mm@kvack.org>,
        LKML <linux-kernel@vger.kernel.org>
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2016-05-04 17:53 GMT+09:00 Michal Hocko <mhocko@kernel.org>:
> On Wed 04-05-16 15:01:24, Joonsoo Kim wrote:
>> On Wed, Apr 20, 2016 at 03:47:25PM -0400, Michal Hocko wrote:
> [...]
>
> Please try to trim your responses it makes it much easier to follow the
> discussion

Okay.

>> > +static inline bool
>> > +should_compact_retry(unsigned int order, enum compact_result compact_result,
>> > +                enum migrate_mode *migrate_mode,
>> > +                int compaction_retries)
>> > +{
>> > +   if (!order)
>> > +           return false;
>> > +
>> > +   /*
>> > +    * compaction considers all the zone as desperately out of memory
>> > +    * so it doesn't really make much sense to retry except when the
>> > +    * failure could be caused by weak migration mode.
>> > +    */
>> > +   if (compaction_failed(compact_result)) {
>>
>> IIUC, this compaction_failed() means that at least one zone is
>> compacted and failed. This is not same with your assumption in the
>> comment. If compaction is done and failed on ZONE_DMA, it would be
>> premature decision.
>
> Not really, because if other zones are making some progress then their
> result will override COMPACT_COMPLETE

Think about the situation that DMA zone fails to compact and
the other zones are deferred or skipped. In this case, COMPACT_COMPLETE
will be returned as a final result and should_compact_retry() return false.
I don't think that it means all the zones are desperately out of memory.

Thanks.