From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 44ABCC43441 for ; Wed, 14 Nov 2018 09:01:02 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 16045214F1 for ; Wed, 14 Nov 2018 09:01:02 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 16045214F1 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732475AbeKNTDU (ORCPT ); Wed, 14 Nov 2018 14:03:20 -0500 Received: from mx1.redhat.com ([209.132.183.28]:45276 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727595AbeKNTDK (ORCPT ); Wed, 14 Nov 2018 14:03:10 -0500 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id C68953078ADC; Wed, 14 Nov 2018 09:00:49 +0000 (UTC) Received: from localhost (ovpn-8-29.pek2.redhat.com [10.72.8.29]) by smtp.corp.redhat.com (Postfix) with ESMTPS id C4C9760C6D; Wed, 14 Nov 2018 09:00:44 +0000 (UTC) Date: Wed, 14 Nov 2018 17:00:42 +0800 From: Baoquan He To: David Hildenbrand Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, mhocko@suse.com, akpm@linux-foundation.org, aarcange@redhat.com Subject: Re: Memory hotplug softlock issue Message-ID: <20181114090042.GD2653@MiWiFi-R3L-srv> References: <20181114070909.GB2653@MiWiFi-R3L-srv> <5a6c6d6b-ebcd-8bfa-d6e0-4312bfe86586@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <5a6c6d6b-ebcd-8bfa-d6e0-4312bfe86586@redhat.com> User-Agent: Mutt/1.9.1 (2017-09-22) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.48]); Wed, 14 Nov 2018 09:00:50 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi David, On 11/14/18 at 09:18am, David Hildenbrand wrote: > Code seems to be waiting for the mem_hotplug_lock in read. > We hold mem_hotplug_lock in write whenever we online/offline/add/remove > memory. There are two ways to trigger offlining of memory: > > 1. Offlining via "cat offline > /sys/devices/system/memory/memory0/state" > > This always properly took the mem_hotplug_lock. Nothing changed > > 2. Offlining via "cat 0 > /sys/devices/system/memory/memory0/online" > > This didn't take the mem_hotplug_lock and I fixed that for this release. > > So if you were testing with 1., you should have seen the same error > before this release (unless there is something else now broken in this > release). Thanks a lot for looking into this. I triggered sysrq+t to check threads' state. You can see that we use firmware to trigger ACPI event to go to acpi_bus_offline(), it truly didn't take mem_hotplug_lock() and has taken it with your fix in commit 381eab4a6ee mm/memory_hotplug: fix online/offline_pages called w.o. mem_hotplug_lock [ +0.007062] Workqueue: kacpi_hotplug acpi_hotplug_work_fn [ +0.005398] Call Trace: [ +0.002476] ? page_vma_mapped_walk+0x307/0x710 [ +0.004538] ? page_remove_rmap+0xa2/0x340 [ +0.004104] ? ptep_clear_flush+0x54/0x60 [ +0.004027] ? enqueue_entity+0x11c/0x620 [ +0.005904] ? schedule+0x28/0x80 [ +0.003336] ? rmap_walk_file+0xf9/0x270 [ +0.003940] ? try_to_unmap+0x9c/0xf0 [ +0.003695] ? migrate_pages+0x2b0/0xb90 [ +0.003959] ? try_offline_node+0x160/0x160 [ +0.004214] ? __offline_pages+0x6ce/0x8e0 [ +0.004134] ? memory_subsys_offline+0x40/0x60 [ +0.004474] ? device_offline+0x81/0xb0 [ +0.003867] ? acpi_bus_offline+0xdb/0x140 [ +0.004117] ? acpi_device_hotplug+0x21c/0x460 [ +0.004458] ? acpi_hotplug_work_fn+0x1a/0x30 [ +0.004372] ? process_one_work+0x1a1/0x3a0 [ +0.004195] ? worker_thread+0x30/0x380 [ +0.003851] ? drain_workqueue+0x120/0x120 [ +0.004117] ? kthread+0x112/0x130 [ +0.003411] ? kthread_park+0x80/0x80 [ +0.005325] ? ret_from_fork+0x35/0x40 > > > The real question is, however, why offlining of the last block doesn't > succeed. In __offline_pages() we basically have an endless loop (while > holding the mem_hotplug_lock in write). Now I consider this piece of > code very problematic (we should automatically fail after X > attempts/after X seconds, we should not ignore -ENOMEM), and we've had > other BUGs whereby we would run into an endless loop here (e.g. related > to hugepages I guess). Hmm, even though memory hotplug stalled there, there are still much memory. E.g in this system, it has 8 nodes and each node has 64 GB memory, it's 512 GB in all. Now I run "stress -m 200" to trigger 200 processes to malloc then free 256 MB contiously, and it's eating 50 GB in all. In theory, it still has much memory for migrating to. > > You mentioned memory pressure, if our host is under memory pressure we > can easily trigger running into an endless loop there, because we > basically ignore -ENOMEM e.g. when we cannot get a page to migrate some > memory to be offlined. I assume this is the case here. > do_migrate_range() could be the bad boy if it keeps failing forever and > we keep retrying. Not sure what other people think about this. If failed the memory removing when still much free memory left, I worry customer will complain. Yeah, it stoped at do_migrate_range() when try to migrate the last memory block. And each time it's the last memory block which can't be offlined and hang. If any message or information needed, I can provide. Thanks Baoquan