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Date:   Thu, 5 Apr 2018 10:27:08 +0200
From:   Michal Hocko <mhocko@kernel.org>
To:     Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
        Mel Gorman <mgorman@suse.de>, Vlastimil Babka <vbabka@suse.cz>,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] mm/thp: don't count ZONE_MOVABLE as the target for
 freepage reserving
Message-ID: <20180405082708.GA6312@dhcp22.suse.cz>
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 <20180405075753.GZ6312@dhcp22.suse.cz>
 <20180405080539.GA631@js1304-desktop>
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On Thu 05-04-18 17:05:39, Joonsoo Kim wrote:
> On Thu, Apr 05, 2018 at 09:57:53AM +0200, Michal Hocko wrote:
> > On Thu 05-04-18 16:27:16, Joonsoo Kim wrote:
> > > From: Joonsoo Kim <iamjoonsoo.kim@lge.com>
> > > 
> > > ZONE_MOVABLE only has movable pages so we don't need to keep enough
> > > freepages to avoid or deal with fragmentation. So, don't count it.
> > > 
> > > This changes min_free_kbytes and thus min_watermark greatly
> > > if ZONE_MOVABLE is used. It will make the user uses more memory.
> > 
> > OK, but why does it matter. Has anybody seen this as an issue?
> 
> There was a regression report for CMA patchset and I think that it is
> related to this problem. CMA patchset makes the system uses one more
> zone (ZONE_MOVABLE) and then increase min_free_kbytes. It reduces
> usable memory and it could cause regression.
> 
> http://lkml.kernel.org/r/20180102063528.GG30397@yexl-desktop

Then this should be a part of the changelog along with some reproducible
results, please.
-- 
Michal Hocko
SUSE Labs