linux-kernel - Re: [PATCH] mm/page_alloc: don't reserve ZONE_HIGHMEM for ZONE

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Date:   Fri, 25 Aug 2017 09:56:10 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Joonsoo Kim <iamjoonsoo.kim@....com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...e.com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Johannes Weiner <hannes@...xchg.org>,
        "Aneesh Kumar K . V" <aneesh.kumar@...ux.vnet.ibm.com>,
        Minchan Kim <minchan@...nel.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/page_alloc: don't reserve ZONE_HIGHMEM for
 ZONE_MOVABLE request

On 08/25/2017 02:20 AM, Joonsoo Kim wrote:
> On Thu, Aug 24, 2017 at 11:41:58AM +0200, Vlastimil Babka wrote:
> 
> Hmm, this is already pointed by Minchan and I have answered that.
> 
> lkml.kernel.org/r/<20170421013243.GA13966@...304-desktop>
> 
> If you have a better idea, please let me know.

My idea is that size of sysctl_lowmem_reserve_ratio is ZONE_NORMAL+1 and
it has no entries for zones > NORMAL. The
setup_per_zone_lowmem_reserve() is adjusted to only set
lower_zone->lowmem_reserve[j] for idx <= ZONE_NORMAL.

I can't imagine somebody would want override the ratio for HIGHMEM or
MOVABLE
(where it has no effect anyway) so the simplest thing is not to expose
it at all.

> Thanks.
>