linux-kernel - Re: [PATCH] mm/thp: don't count ZONE_MOVABLE as the target for freepage reserving

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Message-ID: <20180405080539.GA631@js1304-desktop>
Date:   Thu, 5 Apr 2018 17:05:39 +0900
From:   Joonsoo Kim <iamjoonsoo.kim@....com>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Mel Gorman <mgorman@...e.de>, Vlastimil Babka <vbabka@...e.cz>,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/thp: don't count ZONE_MOVABLE as the target for
 freepage reserving

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@....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

Thanks.