From mboxrd@z Thu Jan 1 00:00:00 1970 From: Joonsoo Kim Subject: Re: [PATCH] mm/page_alloc: don't reserve ZONE_HIGHMEM for ZONE_MOVABLE request Date: Wed, 4 Apr 2018 09:24:06 +0900 Message-ID: References: <1504672525-17915-1-git-send-email-iamjoonsoo.kim@lge.com> <20170914132452.d5klyizce72rhjaa@dhcp22.suse.cz> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Return-path: In-Reply-To: <20170914132452.d5klyizce72rhjaa@dhcp22.suse.cz> Sender: linux-kernel-owner@vger.kernel.org To: Michal Hocko Cc: Andrew Morton , Vlastimil Babka , Mel Gorman , Johannes Weiner , "Aneesh Kumar K . V" , Minchan Kim , Linux Memory Management List , LKML , Joonsoo Kim , linux-api@vger.kernel.org List-Id: linux-api@vger.kernel.org Hello, Michal. Sorry for a really long delay. 2017-09-14 22:24 GMT+09:00 Michal Hocko : > [Sorry for a later reply] > > On Wed 06-09-17 13:35:25, Joonsoo Kim wrote: >> From: Joonsoo Kim >> >> Freepage on ZONE_HIGHMEM doesn't work for kernel memory so it's not that >> important to reserve. > > I am still not convinced this is a good idea. I do agree that reserving > memory in both HIGHMEM and MOVABLE is just wasting memory but removing > the reserve from the highmem as well will result that an oom victim will > allocate from lower zones and that might have unexpected side effects. Looks like you are confused. This patch only affects the situation that ZONE_HIGHMEM and ZONE_MOVABLE is used at the same time. In that case, before this patch, ZONE_HIGHMEM has reserve for GFP_HIGHMEM | GFP_MOVABLE request, but, with this patch, no reserve in ZONE_HIGHMEM for GFP_HIGHMEM | GFP_MOVABLE request. This perfectly matchs with your hope. :) > Can we simply leave HIGHMEM reserve and only remove it from the movable > zone if both are present? There is no higher zone than ZONE_MOVABLE so ZONE_MOVABLE has no reserve with/without this patch. To save memory, we need to remove the reserve in ZONE_HIGHMEM. Thanks.