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V" , Minchan Kim , Linux Memory Management List , LKML , Joonsoo Kim , linux-api@vger.kernel.org Subject: Re: [PATCH] mm/page_alloc: don't reserve ZONE_HIGHMEM for ZONE_MOVABLE request Message-ID: <20180412120133.GD23400@dhcp22.suse.cz> 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=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.9.4 (2018-02-28) 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: On Wed 04-04-18 09:24:06, Joonsoo Kim wrote: > 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. :) I have forgot all the details but my vague recollection is that the concern was that GFP_HIGHUSER_MOVABLE etc. wouldn't keep any reserve in the highmem zone and so emergency allocations - e.g. those during OOM will have to fallback to kernel zones and might lead to hard to predict results. Am I still confused and this will not happen after the patch? -- Michal Hocko SUSE Labs