Date: Mon, 7 Dec 2015 17:18:21 +0100
From: Michal Hocko <mhocko@kernel.org>
To: "Huang, Ying" <ying.huang@linux.intel.com>
Cc: Mel Gorman <mgorman@techsingularity.net>, lkp@01.org,
        LKML <linux-kernel@vger.kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Rik van Riel <riel@redhat.com>, Vitaly Wool <vitalywool@gmail.com>,
        David Rientjes <rientjes@google.com>, Christoph Lameter <cl@linux.com>,
        Johannes Weiner <hannes@cmpxchg.org>, Vlastimil Babka <vbabka@suse.cz>,
        Will Deacon <will.deacon@arm.com>,
        Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [lkp] [mm, page_alloc] d0164adc89: -100.0% fsmark.app_overhead
Message-ID: <20151207161820.GB20774@dhcp22.suse.cz>
References: <20151127100647.GH14880@techsingularity.net>
 <87h9k4kzcv.fsf@yhuang-dev.intel.com>
 <20151202110009.GA2015@techsingularity.net>
 <20151202120046.GE25284@dhcp22.suse.cz>
 <20151202140845.GA19677@suse.de>
 <20151202141529.GG25284@dhcp22.suse.cz>
 <20151202144525.GC2015@techsingularity.net>
 <87k2ovyl4y.fsf@yhuang-dev.intel.com>
 <20151203101719.GG2015@techsingularity.net>
 <87wpsvkmhs.fsf@yhuang-dev.intel.com>
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On Fri 04-12-15 09:53:35, Huang, Ying wrote:
> Mel Gorman <mgorman@techsingularity.net> writes:
[...]
> > What is the result of the __GFP_HIGH patch to give it access to
> > reserves?
> 
> Applied Michal's patch on v4.4-rc3 and tested again, now there is no
> page allocation failure.

I still think this is just a coincidence and __GFP_HIGH just
papers over it (it still makes sense for other reasons though). It
would be better imho to log all allocations which do not include
___GFP_KSWAPD_RECLAIM. This might help us to pin point a caller which
was previously waking kswapd up but it doesn't do so anymore.  There
would have to be a very specific pattern to trigger this because most
allocations would simply wake kswapd up. I am just wondering that
any debugging would simply alter the timing and/or allocation pattern
and we would see a different results so I am not sure this is worth
spending a lot of time on.

-- 
Michal Hocko
SUSE Labs
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