Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752283AbdGaPyB (ORCPT ); Mon, 31 Jul 2017 11:54:01 -0400 Received: from mx2.suse.de ([195.135.220.15]:54416 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751046AbdGaPyA (ORCPT ); Mon, 31 Jul 2017 11:54:00 -0400 Date: Mon, 31 Jul 2017 17:53:50 +0200 From: Michal Hocko To: Gerald Schaefer Cc: Jerome Glisse , linux-mm@kvack.org, Andrew Morton , Mel Gorman , Vlastimil Babka , Andrea Arcangeli , Reza Arbab , Yasuaki Ishimatsu , qiuxishi@huawei.com, Kani Toshimitsu , slaoub@gmail.com, Joonsoo Kim , Andi Kleen , Daniel Kiper , Igor Mammedov , Vitaly Kuznetsov , LKML , Benjamin Herrenschmidt , Catalin Marinas , Dan Williams , Fenghua Yu , Heiko Carstens , "H. Peter Anvin" , Ingo Molnar , Martin Schwidefsky , Michael Ellerman , Paul Mackerras , Thomas Gleixner , Tony Luck , Will Deacon Subject: Re: [RFC PATCH 0/5] mm, memory_hotplug: allocate memmap from hotadded memory Message-ID: <20170731155350.GA1189@dhcp22.suse.cz> References: <20170726083333.17754-1-mhocko@kernel.org> <20170726210657.GE21717@redhat.com> <20170727065652.GE20970@dhcp22.suse.cz> <20170728121941.GL2274@dhcp22.suse.cz> <20170731143521.5809a6ca@thinkpad> <20170731125319.GA4829@dhcp22.suse.cz> <20170731170459.613d5cbd@thinkpad> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170731170459.613d5cbd@thinkpad> 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: 3792 Lines: 76 On Mon 31-07-17 17:04:59, Gerald Schaefer wrote: > On Mon, 31 Jul 2017 14:53:19 +0200 > Michal Hocko wrote: > > > On Mon 31-07-17 14:35:21, Gerald Schaefer wrote: > > > On Fri, 28 Jul 2017 14:19:41 +0200 > > > Michal Hocko wrote: > > > > > > > On Thu 27-07-17 08:56:52, Michal Hocko wrote: > > > > > On Wed 26-07-17 17:06:59, Jerome Glisse wrote: > > > > > [...] > > > > > > This does not seems to be an opt-in change ie if i am reading patch 3 > > > > > > correctly if an altmap is not provided to __add_pages() you fallback > > > > > > to allocating from begining of zone. This will not work with HMM ie > > > > > > device private memory. So at very least i would like to see some way > > > > > > to opt-out of this. Maybe a new argument like bool forbid_altmap ? > > > > > > > > > > OK, I see! I will think about how to make a sane api for that. > > > > > > > > This is what I came up with. s390 guys mentioned that I cannot simply > > > > use the new range at this stage yet. This will need probably some other > > > > changes but I guess we want an opt-in approach with an arch veto in general. > > > > > > > > So what do you think about the following? Only x86 is update now and I > > > > will split it into two parts but the idea should be clear at least. > > > > > > This looks good, and the kernel will also boot again on s390 when applied > > > on top of the other 5 patches (plus adding the s390 part here). > > > > Thanks for testing Gerald! I am still undecided whether the arch code > > should veto MHP_RANGE_ACCESSIBLE if it cannot be supported or just set > > it when it is supported. My last post did the later but the first one > > sounds like a more clear API to me. I will keep thinking about it. > > > > Anyway, did you have any chance to consider mapping the new physical > > memory range inside arch_add_memory rather than during online on s390? > > Well, it still looks like we cannot do w/o splitting up add_memory(): > 1) (only) set up section map during our initial memory detection, w/o > allocating struct pages, so that the sysfs entries get created also for > our offline memory (or else we have no way to online it later) > 2) set up vmemmap and allocate struct pages with your new altmap approach > during our MEM_GOING_ONLINE callback, because only now the memory is really > accessible As I've tried to mentioned in my other response. This is not possible because there are memory hotplug usecases which never do an explicit online. I am sorry to ask again. But why exactly cannot we make the range accessible from arch_add_memory on s390? > Besides the obvious problem that this would need a new interface, there is > also the problem that (at least) show_valid_zones() in drivers/base/memory.c > operates on struct pages from _offline_ memory, for its page_zone() checks. > This will not work well if we have no struct pages for offline memory ... Yes. > BTW, the latter may also be a issue with your rework on any architecture. > Not sure if I understood it correctly, but the situation on s390 (i.e. > having offline memory blocks visible in sysfs) should be similar to > the scenario on x86, when you plug in memory, set it online in the acpi > handler, and then manually set it offline again via sysfs. Now the > memory is still visible in sysfs, and reading the valid_zones attribute > will trigger an access to struct pages for that memory. What if this > memory is now physically removed, in a race with such a struct page > access? The memmap goes away together with the whole section tear down. And we shouldn't have any users of any struct page by that time. Memblock sysfs should be down as well. I will go and double check whether there are any possible races. -- Michal Hocko SUSE Labs