From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ot1-f71.google.com (mail-ot1-f71.google.com [209.85.210.71]) by kanga.kvack.org (Postfix) with ESMTP id 45C856B037F for ; Mon, 29 Oct 2018 11:50:00 -0400 (EDT) Received: by mail-ot1-f71.google.com with SMTP id l92so6755592otc.12 for ; Mon, 29 Oct 2018 08:50:00 -0700 (PDT) Received: from mail-sor-f65.google.com (mail-sor-f65.google.com. [209.85.220.65]) by mx.google.com with SMTPS id m12sor9971116otl.31.2018.10.29.08.49.58 for (Google Transport Security); Mon, 29 Oct 2018 08:49:58 -0700 (PDT) MIME-Version: 1.0 References: <20181009170051.GA40606@tiger-server> <25092df0-b7b4-d456-8409-9c004cb6e422@linux.intel.com> <20181010095838.GG5873@dhcp22.suse.cz> <20181010172451.GK5873@dhcp22.suse.cz> <98c35e19-13b9-0913-87d9-b3f1ab738b61@linux.intel.com> <20181010185242.GP5873@dhcp22.suse.cz> <20181011085509.GS5873@dhcp22.suse.cz> <6f32f23c-c21c-9d42-7dda-a1d18613cd3c@linux.intel.com> <20181017075257.GF18839@dhcp22.suse.cz> <971729e6-bcfe-a386-361b-d662951e69a7@linux.intel.com> In-Reply-To: <971729e6-bcfe-a386-361b-d662951e69a7@linux.intel.com> From: Dan Williams Date: Mon, 29 Oct 2018 08:49:46 -0700 Message-ID: Subject: Re: [PATCH v5 4/4] mm: Defer ZONE_DEVICE page initialization to the point where we init pgmap Content-Type: text/plain; charset="UTF-8" Sender: owner-linux-mm@kvack.org List-ID: To: alexander.h.duyck@linux.intel.com Cc: Michal Hocko , Linux MM , Andrew Morton , Linux Kernel Mailing List , linux-nvdimm , Pasha Tatashin , Dave Hansen , =?UTF-8?B?SsOpcsO0bWUgR2xpc3Nl?= , rppt@linux.vnet.ibm.com, Ingo Molnar , "Kirill A. Shutemov" , Zhang Yi On Wed, Oct 17, 2018 at 8:02 AM Alexander Duyck wrote: > > On 10/17/2018 12:52 AM, Michal Hocko wrote: > > On Thu 11-10-18 10:38:39, Alexander Duyck wrote: > >> On 10/11/2018 1:55 AM, Michal Hocko wrote: > >>> On Wed 10-10-18 20:52:42, Michal Hocko wrote: > >>> [...] > >>>> My recollection was that we do clear the reserved bit in > >>>> move_pfn_range_to_zone and we indeed do in __init_single_page. But then > >>>> we set the bit back right afterwards. This seems to be the case since > >>>> d0dc12e86b319 which reorganized the code. I have to study this some more > >>>> obviously. > >>> > >>> so my recollection was wrong and d0dc12e86b319 hasn't really changed > >>> much because __init_single_page wouldn't zero out the struct page for > >>> the hotplug contex. A comment in move_pfn_range_to_zone explains that we > >>> want the reserved bit because pfn walkers already do see the pfn range > >>> and the page is not fully associated with the zone until it is onlined. > >>> > >>> I am thinking that we might be overzealous here. With the full state > >>> initialized we shouldn't actually care. pfn_to_online_page should return > >>> NULL regardless of the reserved bit and normal pfn walkers shouldn't > >>> touch pages they do not recognize and a plain page with ref. count 1 > >>> doesn't tell much to anybody. So I _suspect_ that we can simply drop the > >>> reserved bit setting here. > >> > >> So this has me a bit hesitant to want to just drop the bit entirely. If > >> nothing else I think I may wan to make that a patch onto itself so that if > >> we aren't going to set it we just drop it there. That way if it does cause > >> issues we can bisect it to that patch and pinpoint the cause. > > > > Yes a patch on its own make sense for bisectability. > > For now I think I am going to back off of this. There is a bunch of > other changes that need to happen in order for us to make this work. As > far as I can tell there are several places that are relying on this > reserved bit. When David Hildebrand and I looked it was only the hibernation code that we thought needed changing. We either need to audit the removal or go back to adding a special case hack for kvm because this is a blocking issue for them. What do you see beyond the hibernation change?