From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751290AbdJWFTU (ORCPT ); Mon, 23 Oct 2017 01:19:20 -0400 Received: from LGEAMRELO13.lge.com ([156.147.23.53]:57415 "EHLO lgeamrelo13.lge.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750885AbdJWFTT (ORCPT ); Mon, 23 Oct 2017 01:19:19 -0400 X-Original-SENDERIP: 156.147.1.121 X-Original-MAILFROM: iamjoonsoo.kim@lge.com X-Original-SENDERIP: 10.177.222.138 X-Original-MAILFROM: iamjoonsoo.kim@lge.com Date: Mon, 23 Oct 2017 14:23:09 +0900 From: Joonsoo Kim To: Michal Hocko Cc: linux-mm@kvack.org, Michael Ellerman , Vlastimil Babka , Andrew Morton , KAMEZAWA Hiroyuki , Reza Arbab , Yasuaki Ishimatsu , qiuxishi@huawei.com, Igor Mammedov , Vitaly Kuznetsov , LKML Subject: Re: [PATCH 1/2] mm: drop migrate type checks from has_unmovable_pages Message-ID: <20171023052309.GB23082@js1304-P5Q-DELUXE> References: <20171013120013.698-1-mhocko@kernel.org> <20171019025111.GA3852@js1304-P5Q-DELUXE> <20171019071503.e7w5fo35lsq6ca54@dhcp22.suse.cz> <20171019073355.GA4486@js1304-P5Q-DELUXE> <20171019082041.5zudpqacaxjhe4gw@dhcp22.suse.cz> <20171019122118.y6cndierwl2vnguj@dhcp22.suse.cz> <20171020021329.GB10438@js1304-P5Q-DELUXE> <20171020055922.x2mj6j66obmp52da@dhcp22.suse.cz> <20171020065014.GA11145@js1304-P5Q-DELUXE> <20171020070220.t4o573zymgto5kmi@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20171020070220.t4o573zymgto5kmi@dhcp22.suse.cz> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Oct 20, 2017 at 09:02:20AM +0200, Michal Hocko wrote: > On Fri 20-10-17 15:50:14, Joonsoo Kim wrote: > > On Fri, Oct 20, 2017 at 07:59:22AM +0200, Michal Hocko wrote: > > > On Fri 20-10-17 11:13:29, Joonsoo Kim wrote: > > > > On Thu, Oct 19, 2017 at 02:21:18PM +0200, Michal Hocko wrote: > > > > > On Thu 19-10-17 10:20:41, Michal Hocko wrote: > > > > > > On Thu 19-10-17 16:33:56, Joonsoo Kim wrote: > > > > > > > On Thu, Oct 19, 2017 at 09:15:03AM +0200, Michal Hocko wrote: > > > > > > > > On Thu 19-10-17 11:51:11, Joonsoo Kim wrote: > > > > > > [...] > > > > > > > > > Hello, > > > > > > > > > > > > > > > > > > This patch will break the CMA user. As you mentioned, CMA allocation > > > > > > > > > itself isn't migrateable. So, after a single page is allocated through > > > > > > > > > CMA allocation, has_unmovable_pages() will return true for this > > > > > > > > > pageblock. Then, futher CMA allocation request to this pageblock will > > > > > > > > > fail because it requires isolating the pageblock. > > > > > > > > > > > > > > > > Hmm, does this mean that the CMA allocation path depends on > > > > > > > > has_unmovable_pages to return false here even though the memory is not > > > > > > > > movable? This sounds really strange to me and kind of abuse of this > > > > > > > > > > > > > > Your understanding is correct. Perhaps, abuse or wrong function name. > > > > > > > > > > > > > > > function. Which path is that? Can we do the migrate type test theres? > > > > > > > > > > > > > > alloc_contig_range() -> start_isolate_page_range() -> > > > > > > > set_migratetype_isolate() -> has_unmovable_pages() > > > > > > > > > > > > I see. It seems that the CMA and memory hotplug have a very different > > > > > > view on what should happen during isolation. > > > > > > > > > > > > > We can add one argument, 'XXX' to set_migratetype_isolate() and change > > > > > > > it to check migrate type rather than has_unmovable_pages() if 'XXX' is > > > > > > > specified. > > > > > > > > > > > > Can we use the migratetype argument and do the special thing for > > > > > > MIGRATE_CMA? Like the following diff? > > > > > > > > > > And with the full changelog. > > > > > --- > > > > > >From 8cbd811d741f5dd93d1b21bb3ef94482a4d0bd32 Mon Sep 17 00:00:00 2001 > > > > > From: Michal Hocko > > > > > Date: Thu, 19 Oct 2017 14:14:02 +0200 > > > > > Subject: [PATCH] mm: distinguish CMA and MOVABLE isolation in > > > > > has_unmovable_pages > > > > > > > > > > Joonsoo has noticed that "mm: drop migrate type checks from > > > > > has_unmovable_pages" would break CMA allocator because it relies on > > > > > has_unmovable_pages returning false even for CMA pageblocks which in > > > > > fact don't have to be movable: > > > > > alloc_contig_range > > > > > start_isolate_page_range > > > > > set_migratetype_isolate > > > > > has_unmovable_pages > > > > > > > > > > This is a result of the code sharing between CMA and memory hotplug > > > > > while each one has a different idea of what has_unmovable_pages should > > > > > return. This is unfortunate but fixing it properly would require a lot > > > > > of code duplication. > > > > > > > > > > Fix the issue by introducing the requested migrate type argument > > > > > and special case MIGRATE_CMA case where CMA page blocks are handled > > > > > properly. This will work for memory hotplug because it requires > > > > > MIGRATE_MOVABLE. > > > > > > > > Unfortunately, alloc_contig_range() can be called with > > > > MIGRATE_MOVABLE so this patch cannot perfectly fix the problem. > > > > > > Yes, alloc_contig_range can be called with MIGRATE_MOVABLE but my > > > understanding is that only CMA allocator really depends on this weird > > > semantic and that does MIGRATE_CMA unconditionally. > > > > alloc_contig_range() could be called for partial pages in the > > pageblock. With your patch, this case also fails unnecessarilly if the > > other pages in the pageblock is pinned. > > Is this really the case for GB pages? Do we really want to mess those No, but, as I mentioned already, this API can be called with less pages. I know that there is no user with less pages at this moment but I cannot see any point to reduce this API's capability. > with CMA blocks and make those blocks basically unusable because GB > pages are rarely (if at all migrateable)? > > > Until now, there is no user calling alloc_contig_range() with partial > > pages except CMA allocator but API could support it. > > I disagree. If this is a CMA thing it should stay that way. The semantic > is quite confusing already, please let's not make it even worse. It is already used by other component. I'm not sure what is the confusing semantic you mentioned. I think that set_migratetype_isolate() has confusing semantic and should be fixed since making the pageblock isolated doesn't need to check if there is unmovable page or not. Do you think that set_migratetype_isolate() need to check it? If so, why? > > > > I did a more thinking and found that it's strange to check if there is > > > > unmovable page in the pageblock during the set_migratetype_isolate(). > > > > set_migratetype_isolate() should be just for setting the migratetype > > > > of the pageblock. Checking other things should be done by another > > > > place, for example, before calling the start_isolate_page_range() in > > > > __offline_pages(). > > > > > > How do we guarantee the atomicity? > > > > What atomicity do you mean? > > Currently we are checking and isolating pages under zone lock. If we > split that we are losing atomicity, aren't we. I think that it can be done easily. set_migratetype_isolate() { lock __set_migratetype_isolate(); unlock } set_migratetype_isolate_if_no_unmovable_pages() { lock if (has_unmovable_pages()) fail else __set_migratetype_isolate() unlock } Thanks. From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pg0-f71.google.com (mail-pg0-f71.google.com [74.125.83.71]) by kanga.kvack.org (Postfix) with ESMTP id E06956B0069 for ; Mon, 23 Oct 2017 01:19:17 -0400 (EDT) Received: by mail-pg0-f71.google.com with SMTP id a192so11004061pge.1 for ; Sun, 22 Oct 2017 22:19:17 -0700 (PDT) Received: from lgeamrelo13.lge.com (LGEAMRELO13.lge.com. [156.147.23.53]) by mx.google.com with ESMTP id w1si4365785pgq.644.2017.10.22.22.19.16 for ; Sun, 22 Oct 2017 22:19:16 -0700 (PDT) Date: Mon, 23 Oct 2017 14:23:09 +0900 From: Joonsoo Kim Subject: Re: [PATCH 1/2] mm: drop migrate type checks from has_unmovable_pages Message-ID: <20171023052309.GB23082@js1304-P5Q-DELUXE> References: <20171013120013.698-1-mhocko@kernel.org> <20171019025111.GA3852@js1304-P5Q-DELUXE> <20171019071503.e7w5fo35lsq6ca54@dhcp22.suse.cz> <20171019073355.GA4486@js1304-P5Q-DELUXE> <20171019082041.5zudpqacaxjhe4gw@dhcp22.suse.cz> <20171019122118.y6cndierwl2vnguj@dhcp22.suse.cz> <20171020021329.GB10438@js1304-P5Q-DELUXE> <20171020055922.x2mj6j66obmp52da@dhcp22.suse.cz> <20171020065014.GA11145@js1304-P5Q-DELUXE> <20171020070220.t4o573zymgto5kmi@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20171020070220.t4o573zymgto5kmi@dhcp22.suse.cz> Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko Cc: linux-mm@kvack.org, Michael Ellerman , Vlastimil Babka , Andrew Morton , KAMEZAWA Hiroyuki , Reza Arbab , Yasuaki Ishimatsu , qiuxishi@huawei.com, Igor Mammedov , Vitaly Kuznetsov , LKML On Fri, Oct 20, 2017 at 09:02:20AM +0200, Michal Hocko wrote: > On Fri 20-10-17 15:50:14, Joonsoo Kim wrote: > > On Fri, Oct 20, 2017 at 07:59:22AM +0200, Michal Hocko wrote: > > > On Fri 20-10-17 11:13:29, Joonsoo Kim wrote: > > > > On Thu, Oct 19, 2017 at 02:21:18PM +0200, Michal Hocko wrote: > > > > > On Thu 19-10-17 10:20:41, Michal Hocko wrote: > > > > > > On Thu 19-10-17 16:33:56, Joonsoo Kim wrote: > > > > > > > On Thu, Oct 19, 2017 at 09:15:03AM +0200, Michal Hocko wrote: > > > > > > > > On Thu 19-10-17 11:51:11, Joonsoo Kim wrote: > > > > > > [...] > > > > > > > > > Hello, > > > > > > > > > > > > > > > > > > This patch will break the CMA user. As you mentioned, CMA allocation > > > > > > > > > itself isn't migrateable. So, after a single page is allocated through > > > > > > > > > CMA allocation, has_unmovable_pages() will return true for this > > > > > > > > > pageblock. Then, futher CMA allocation request to this pageblock will > > > > > > > > > fail because it requires isolating the pageblock. > > > > > > > > > > > > > > > > Hmm, does this mean that the CMA allocation path depends on > > > > > > > > has_unmovable_pages to return false here even though the memory is not > > > > > > > > movable? This sounds really strange to me and kind of abuse of this > > > > > > > > > > > > > > Your understanding is correct. Perhaps, abuse or wrong function name. > > > > > > > > > > > > > > > function. Which path is that? Can we do the migrate type test theres? > > > > > > > > > > > > > > alloc_contig_range() -> start_isolate_page_range() -> > > > > > > > set_migratetype_isolate() -> has_unmovable_pages() > > > > > > > > > > > > I see. It seems that the CMA and memory hotplug have a very different > > > > > > view on what should happen during isolation. > > > > > > > > > > > > > We can add one argument, 'XXX' to set_migratetype_isolate() and change > > > > > > > it to check migrate type rather than has_unmovable_pages() if 'XXX' is > > > > > > > specified. > > > > > > > > > > > > Can we use the migratetype argument and do the special thing for > > > > > > MIGRATE_CMA? Like the following diff? > > > > > > > > > > And with the full changelog. > > > > > --- > > > > > >From 8cbd811d741f5dd93d1b21bb3ef94482a4d0bd32 Mon Sep 17 00:00:00 2001 > > > > > From: Michal Hocko > > > > > Date: Thu, 19 Oct 2017 14:14:02 +0200 > > > > > Subject: [PATCH] mm: distinguish CMA and MOVABLE isolation in > > > > > has_unmovable_pages > > > > > > > > > > Joonsoo has noticed that "mm: drop migrate type checks from > > > > > has_unmovable_pages" would break CMA allocator because it relies on > > > > > has_unmovable_pages returning false even for CMA pageblocks which in > > > > > fact don't have to be movable: > > > > > alloc_contig_range > > > > > start_isolate_page_range > > > > > set_migratetype_isolate > > > > > has_unmovable_pages > > > > > > > > > > This is a result of the code sharing between CMA and memory hotplug > > > > > while each one has a different idea of what has_unmovable_pages should > > > > > return. This is unfortunate but fixing it properly would require a lot > > > > > of code duplication. > > > > > > > > > > Fix the issue by introducing the requested migrate type argument > > > > > and special case MIGRATE_CMA case where CMA page blocks are handled > > > > > properly. This will work for memory hotplug because it requires > > > > > MIGRATE_MOVABLE. > > > > > > > > Unfortunately, alloc_contig_range() can be called with > > > > MIGRATE_MOVABLE so this patch cannot perfectly fix the problem. > > > > > > Yes, alloc_contig_range can be called with MIGRATE_MOVABLE but my > > > understanding is that only CMA allocator really depends on this weird > > > semantic and that does MIGRATE_CMA unconditionally. > > > > alloc_contig_range() could be called for partial pages in the > > pageblock. With your patch, this case also fails unnecessarilly if the > > other pages in the pageblock is pinned. > > Is this really the case for GB pages? Do we really want to mess those No, but, as I mentioned already, this API can be called with less pages. I know that there is no user with less pages at this moment but I cannot see any point to reduce this API's capability. > with CMA blocks and make those blocks basically unusable because GB > pages are rarely (if at all migrateable)? > > > Until now, there is no user calling alloc_contig_range() with partial > > pages except CMA allocator but API could support it. > > I disagree. If this is a CMA thing it should stay that way. The semantic > is quite confusing already, please let's not make it even worse. It is already used by other component. I'm not sure what is the confusing semantic you mentioned. I think that set_migratetype_isolate() has confusing semantic and should be fixed since making the pageblock isolated doesn't need to check if there is unmovable page or not. Do you think that set_migratetype_isolate() need to check it? If so, why? > > > > I did a more thinking and found that it's strange to check if there is > > > > unmovable page in the pageblock during the set_migratetype_isolate(). > > > > set_migratetype_isolate() should be just for setting the migratetype > > > > of the pageblock. Checking other things should be done by another > > > > place, for example, before calling the start_isolate_page_range() in > > > > __offline_pages(). > > > > > > How do we guarantee the atomicity? > > > > What atomicity do you mean? > > Currently we are checking and isolating pages under zone lock. If we > split that we are losing atomicity, aren't we. I think that it can be done easily. set_migratetype_isolate() { lock __set_migratetype_isolate(); unlock } set_migratetype_isolate_if_no_unmovable_pages() { lock if (has_unmovable_pages()) fail else __set_migratetype_isolate() unlock } Thanks. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org