Re: [PATCH] mm/page_alloc: don't reserve ZONE_HIGHMEM for ZONE_MOVABLE request

From: Michal Hocko <mhocko@kernel.org>
To: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Vlastimil Babka <vbabka@suse.cz>,
	Mel Gorman <mgorman@techsingularity.net>,
	Johannes Weiner <hannes@cmpxchg.org>,
	"Aneesh Kumar K . V" <aneesh.kumar@linux.vnet.ibm.com>,
	Minchan Kim <minchan@kernel.org>,
	linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] mm/page_alloc: don't reserve ZONE_HIGHMEM for ZONE_MOVABLE request
Date: Fri, 25 Aug 2017 09:33:14 +0200	[thread overview]
Message-ID: <20170825073314.GC25498@dhcp22.suse.cz> (raw)
In-Reply-To: <20170825001543.GC29701@js1304-P5Q-DELUXE>

On Fri 25-08-17 09:15:43, Joonsoo Kim wrote:
> On Thu, Aug 24, 2017 at 11:30:50AM +0200, Michal Hocko wrote:
> > On Thu 24-08-17 14:45:46, Joonsoo Kim wrote:
> > > From: Joonsoo Kim <iamjoonsoo.kim@lge.com>
> > > 
> > > Freepage on ZONE_HIGHMEM doesn't work for kernel memory so it's not that
> > > important to reserve. When ZONE_MOVABLE is used, this problem would
> > > theorectically cause to decrease usable memory for GFP_HIGHUSER_MOVABLE
> > > allocation request which is mainly used for page cache and anon page
> > > allocation. So, fix it.
> > 
> > I do not really understand what is the problem you are trying to fix.
> > Yes the memory is reserved for a higher priority consumer and that is
> > deliberate AFAICT. Just consider that an OOM victim wants to make
> > further progress and rely on memory reserve while doing
> > GFP_HIGHUSER_MOVABLE request.
> > 
> > So what is the real problem you are trying to address here?
> 
> If the system has the both, ZONE_HIGHMEM and ZONE_MOVABLE,
> ZONE_HIGHMEM will reserve the memory for ZONE_MOVABLE request.

Ohh, right. I forgot that __GFP_MOVABLE doesn't really enforce the
movable zone. It does so only if __GFP_HIGHMEM is specified as well when
ZONE_HIGHMEM is enabled. So indeed reserving memory in both is somehow
awkward. So why don't we simply remove reserves from the movable zone
when the highmem zone is enabled?
-- 
Michal Hocko
SUSE Labs

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>