From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751735AbdJSHaS (ORCPT ); Thu, 19 Oct 2017 03:30:18 -0400 Received: from LGEAMRELO13.lge.com ([156.147.23.53]:41317 "EHLO lgeamrelo13.lge.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751611AbdJSHaR (ORCPT ); Thu, 19 Oct 2017 03:30:17 -0400 X-Original-SENDERIP: 156.147.1.127 X-Original-MAILFROM: iamjoonsoo.kim@lge.com X-Original-SENDERIP: 10.177.222.138 X-Original-MAILFROM: iamjoonsoo.kim@lge.com Date: Thu, 19 Oct 2017 16:33:56 +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: <20171019073355.GA4486@js1304-P5Q-DELUXE> References: <20171013115835.zaehapuucuzl2vlv@dhcp22.suse.cz> <20171013120013.698-1-mhocko@kernel.org> <20171019025111.GA3852@js1304-P5Q-DELUXE> <20171019071503.e7w5fo35lsq6ca54@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20171019071503.e7w5fo35lsq6ca54@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 Thu, Oct 19, 2017 at 09:15:03AM +0200, Michal Hocko wrote: > On Thu 19-10-17 11:51:11, Joonsoo Kim wrote: > > On Fri, Oct 13, 2017 at 02:00:12PM +0200, Michal Hocko wrote: > > > From: Michal Hocko > > > > > > Michael has noticed that the memory offline tries to migrate kernel code > > > pages when doing > > > echo 0 > /sys/devices/system/memory/memory0/online > > > > > > The current implementation will fail the operation after several failed > > > page migration attempts but we shouldn't even attempt to migrate > > > that memory and fail right away because this memory is clearly not > > > migrateable. This will become a real problem when we drop the retry loop > > > counter resp. timeout. > > > > > > The real problem is in has_unmovable_pages in fact. We should fail if > > > there are any non migrateable pages in the area. In orther to guarantee > > > that remove the migrate type checks because MIGRATE_MOVABLE is not > > > guaranteed to contain only migrateable pages. It is merely a heuristic. > > > Similarly MIGRATE_CMA does guarantee that the page allocator doesn't > > > allocate any non-migrateable pages from the block but CMA allocations > > > themselves are unlikely to migrateable. Therefore remove both checks. > > > > 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() 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. Thanks. From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-f199.google.com (mail-pf0-f199.google.com [209.85.192.199]) by kanga.kvack.org (Postfix) with ESMTP id 7854E6B0033 for ; Thu, 19 Oct 2017 03:30:18 -0400 (EDT) Received: by mail-pf0-f199.google.com with SMTP id v2so5182336pfa.10 for ; Thu, 19 Oct 2017 00:30:18 -0700 (PDT) Received: from lgeamrelo13.lge.com (LGEAMRELO13.lge.com. [156.147.23.53]) by mx.google.com with ESMTP id k70si5178008pgc.344.2017.10.19.00.30.16 for ; Thu, 19 Oct 2017 00:30:17 -0700 (PDT) Date: Thu, 19 Oct 2017 16:33:56 +0900 From: Joonsoo Kim Subject: Re: [PATCH 1/2] mm: drop migrate type checks from has_unmovable_pages Message-ID: <20171019073355.GA4486@js1304-P5Q-DELUXE> References: <20171013115835.zaehapuucuzl2vlv@dhcp22.suse.cz> <20171013120013.698-1-mhocko@kernel.org> <20171019025111.GA3852@js1304-P5Q-DELUXE> <20171019071503.e7w5fo35lsq6ca54@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20171019071503.e7w5fo35lsq6ca54@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 Thu, Oct 19, 2017 at 09:15:03AM +0200, Michal Hocko wrote: > On Thu 19-10-17 11:51:11, Joonsoo Kim wrote: > > On Fri, Oct 13, 2017 at 02:00:12PM +0200, Michal Hocko wrote: > > > From: Michal Hocko > > > > > > Michael has noticed that the memory offline tries to migrate kernel code > > > pages when doing > > > echo 0 > /sys/devices/system/memory/memory0/online > > > > > > The current implementation will fail the operation after several failed > > > page migration attempts but we shouldn't even attempt to migrate > > > that memory and fail right away because this memory is clearly not > > > migrateable. This will become a real problem when we drop the retry loop > > > counter resp. timeout. > > > > > > The real problem is in has_unmovable_pages in fact. We should fail if > > > there are any non migrateable pages in the area. In orther to guarantee > > > that remove the migrate type checks because MIGRATE_MOVABLE is not > > > guaranteed to contain only migrateable pages. It is merely a heuristic. > > > Similarly MIGRATE_CMA does guarantee that the page allocator doesn't > > > allocate any non-migrateable pages from the block but CMA allocations > > > themselves are unlikely to migrateable. Therefore remove both checks. > > > > 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() 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. 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