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Tue, 3 Apr 2018 20:24:11 -0400 Received: from mail-wr0-f194.google.com ([209.85.128.194]:38367 "EHLO mail-wr0-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756608AbeDDAYI (ORCPT ); Tue, 3 Apr 2018 20:24:08 -0400 X-Google-Smtp-Source: AIpwx49A4MxewlZdW8Ccfp6IlsTJA9UXrUSg96h9jh+H/JkwPVI23VND0SQ0Eg+hvi+iKFu8sg8E8KNjbxNAf5Oz1GQ= MIME-Version: 1.0 In-Reply-To: <20170914132452.d5klyizce72rhjaa@dhcp22.suse.cz> References: <1504672525-17915-1-git-send-email-iamjoonsoo.kim@lge.com> <20170914132452.d5klyizce72rhjaa@dhcp22.suse.cz> From: Joonsoo Kim Date: Wed, 4 Apr 2018 09:24:06 +0900 Message-ID: Subject: Re: [PATCH] mm/page_alloc: don't reserve ZONE_HIGHMEM for ZONE_MOVABLE request 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 Content-Type: text/plain; charset="UTF-8" Sender: linux-api-owner@vger.kernel.org X-Mailing-List: linux-api@vger.kernel.org X-getmail-retrieved-from-mailbox: INBOX X-Mailing-List: linux-kernel@vger.kernel.org List-ID: 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.