Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754636AbdHYHdU (ORCPT ); Fri, 25 Aug 2017 03:33:20 -0400 Received: from mx2.suse.de ([195.135.220.15]:47093 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1754329AbdHYHdS (ORCPT ); Fri, 25 Aug 2017 03:33:18 -0400 Date: Fri, 25 Aug 2017 09:33:14 +0200 From: Michal Hocko To: Joonsoo Kim Cc: Andrew Morton , Vlastimil Babka , Mel Gorman , Johannes Weiner , "Aneesh Kumar K . V" , Minchan Kim , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm/page_alloc: don't reserve ZONE_HIGHMEM for ZONE_MOVABLE request Message-ID: <20170825073314.GC25498@dhcp22.suse.cz> References: <1503553546-27450-1-git-send-email-iamjoonsoo.kim@lge.com> <20170824093050.GD5943@dhcp22.suse.cz> <20170825001543.GC29701@js1304-P5Q-DELUXE> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170825001543.GC29701@js1304-P5Q-DELUXE> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1408 Lines: 30 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 > > > > > > 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