From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qk1-f198.google.com (mail-qk1-f198.google.com [209.85.222.198]) by kanga.kvack.org (Postfix) with ESMTP id 63BB96B0003 for ; Thu, 15 Nov 2018 02:54:03 -0500 (EST) Received: by mail-qk1-f198.google.com with SMTP id w185so43920432qka.9 for ; Wed, 14 Nov 2018 23:54:03 -0800 (PST) Received: from mx1.redhat.com (mx1.redhat.com. [209.132.183.28]) by mx.google.com with ESMTPS id 54si1510700qtm.62.2018.11.14.23.54.02 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 14 Nov 2018 23:54:02 -0800 (PST) Date: Thu, 15 Nov 2018 15:53:56 +0800 From: Baoquan He Subject: Re: Memory hotplug softlock issue Message-ID: <20181115075349.GL2653@MiWiFi-R3L-srv> References: <20181114070909.GB2653@MiWiFi-R3L-srv> <5a6c6d6b-ebcd-8bfa-d6e0-4312bfe86586@redhat.com> <20181114090134.GG23419@dhcp22.suse.cz> <20181114145250.GE2653@MiWiFi-R3L-srv> <20181114150029.GY23419@dhcp22.suse.cz> <20181115051034.GK2653@MiWiFi-R3L-srv> <20181115073052.GA23831@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181115073052.GA23831@dhcp22.suse.cz> Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko Cc: David Hildenbrand , linux-mm@kvack.org, linux-kernel@vger.kernel.org, akpm@linux-foundation.org, aarcange@redhat.com On 11/15/18 at 08:30am, Michal Hocko wrote: > On Thu 15-11-18 13:10:34, Baoquan He wrote: > > On 11/14/18 at 04:00pm, Michal Hocko wrote: > > > On Wed 14-11-18 22:52:50, Baoquan He wrote: > > > > On 11/14/18 at 10:01am, Michal Hocko wrote: > > > > > I have seen an issue when the migration cannot make a forward progress > > > > > because of a glibc page with a reference count bumping up and down. Most > > > > > probable explanation is the faultaround code. I am working on this and > > > > > will post a patch soon. In any case the migration should converge and if > > > > > it doesn't do then there is a bug lurking somewhere. > > > > > > > > > > Failing on ENOMEM is a questionable thing. I haven't seen that happening > > > > > wildly but if it is a case then I wouldn't be opposed. > > > > > > > > Applied your debugging patches, it helps a lot to printing message. > > > > > > > > Below is the dmesg log about the migrating failure. It can't pass > > > > migrate_pages() and loop forever. > > > > > > > > [ +0.083841] migrating pfn 10fff7d0 failed > > > > [ +0.000005] page:ffffea043ffdf400 count:208 mapcount:201 mapping:ffff888dff4bdda8 index:0x2 > > > > [ +0.012689] xfs_address_space_operations [xfs] > > > > [ +0.000030] name:"stress" > > > > [ +0.004556] flags: 0x5fffffc0000004(uptodate) > > > > [ +0.007339] raw: 005fffffc0000004 ffffc900000e3d80 ffffc900000e3d80 ffff888dff4bdda8 > > > > [ +0.009488] raw: 0000000000000002 0000000000000000 000000cb000000c8 ffff888e7353d000 > > > > [ +0.007726] page->mem_cgroup:ffff888e7353d000 > > > > [ +0.084538] migrating pfn 10fff7d0 failed > > > > [ +0.000006] page:ffffea043ffdf400 count:210 mapcount:201 mapping:ffff888dff4bdda8 index:0x2 > > > > [ +0.012798] xfs_address_space_operations [xfs] > > > > [ +0.000034] name:"stress" > > > > [ +0.004524] flags: 0x5fffffc0000004(uptodate) > > > > [ +0.007068] raw: 005fffffc0000004 ffffc900000e3d80 ffffc900000e3d80 ffff888dff4bdda8 > > > > [ +0.009359] raw: 0000000000000002 0000000000000000 000000cb000000c8 ffff888e7353d000 > > > > [ +0.007728] page->mem_cgroup:ffff888e7353d000 > > > > > > I wouldn't be surprised if this was a similar/same issue I've been > > > chasing recently. Could you try to disable faultaround to see if that > > > helps. It seems that it helped in my particular case but I am still > > > waiting for the final good-to-go to post the patch as I do not own the > > > workload which triggered that issue. > > > > Tried, still stuck in last block sometime. Usually after several times > > of hotplug/unplug. If stop stress program, the last block will be > > offlined immediately. > > Is the pattern still the same? I mean failing over few pages with > reference count jumping up and down between attempts? ->count jumping up and down, mapcount stays the same value. > > > [root@ ~]# cat /sys/kernel/debug/fault_around_bytes > > 4096 > > Can you make it 0? I executed 'echo 0 > fault_around_bytes', value less than one page size will round up to one page. /* * fault_around_bytes must be rounded down to the nearest page order as it's * what do_fault_around() expects to see. */ static int fault_around_bytes_set(void *data, u64 val) { if (val / PAGE_SIZE > PTRS_PER_PTE) return -EINVAL; if (val > PAGE_SIZE) fault_around_bytes = rounddown_pow_of_two(val); else fault_around_bytes = PAGE_SIZE; /* rounddown_pow_of_two(0) is undefined */ return 0; }