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=-8.7 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,UNPARSEABLE_RELAY 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 1B4CAC433ED for ; Mon, 12 Apr 2021 05:24:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D83316105A for ; Mon, 12 Apr 2021 05:24:24 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229810AbhDLFYi (ORCPT ); Mon, 12 Apr 2021 01:24:38 -0400 Received: from out20-14.mail.aliyun.com ([115.124.20.14]:39719 "EHLO out20-14.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229676AbhDLFYh (ORCPT ); Mon, 12 Apr 2021 01:24:37 -0400 X-Alimail-AntiSpam: AC=CONTINUE;BC=0.04436332|-1;CH=green;DM=|CONTINUE|false|;DS=CONTINUE|ham_enroll_verification|0.0217706-0.000781028-0.977448;FP=0|0|0|0|0|-1|-1|-1;HT=ay29a033018047206;MF=wangyugui@e16-tech.com;NM=1;PH=DS;RN=4;RT=4;SR=0;TI=SMTPD_---.JyeN.vq_1618205057; Received: from 192.168.2.112(mailfrom:wangyugui@e16-tech.com fp:SMTPD_---.JyeN.vq_1618205057) by smtp.aliyun-inc.com(10.147.40.2); Mon, 12 Apr 2021 13:24:18 +0800 Date: Mon, 12 Apr 2021 13:24:20 +0800 From: Wang Yugui To: Dennis Zhou Subject: Re: unexpected -ENOMEM from percpu_counter_init() Cc: Vlastimil Babka , linux-mm@kvack.org, linux-btrfs@vger.kernel.org In-Reply-To: References: <20210411232000.BF15.409509F4@e16-tech.com> Message-Id: <20210412132419.2BE8.409509F4@e16-tech.com> MIME-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit X-Mailer: Becky! ver. 2.75.03 [en] Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org Hi, > On Sun, Apr 11, 2021 at 11:20:00PM +0800, Wang Yugui wrote: > > Hi, Dennis Zhou > > > > > Hi, > > > > > > > On Sat, Apr 10, 2021 at 11:29:17PM +0800, Wang Yugui wrote: > > > > > Hi, Dennis Zhou > > > > > > > > > > Thanks for your ncie answer. > > > > > but still a few questions. > > > > > > > > > > > Percpu is not really cheap memory to allocate because it has a > > > > > > amplification factor of NR_CPUS. As a result, percpu on the critical > > > > > > path is really not something that is expected to be high throughput. > > > > > > > > > > > Ideally things like btrfs snapshots should preallocate a number of these > > > > > > and not try to do atomic allocations because that in theory could fail > > > > > > because even after we go to the page allocator in the future we can't > > > > > > get enough pages due to needing to go into reclaim. > > > > > > > > > > pre-allocate in module such as mempool_t is just used in a few place in > > > > > linux/fs. so most people like system wide pre-allocate, because it is > > > > > more easy to use? > > > > > > > > > > can we add more chance to management the system wide pre-alloc > > > > > just like this? > > > > > > > > > > diff --git a/include/linux/sched/mm.h b/include/linux/sched/mm.h > > > > > index dc1f4dc..eb3f592 100644 > > > > > --- a/include/linux/sched/mm.h > > > > > +++ b/include/linux/sched/mm.h > > > > > @@ -226,6 +226,11 @@ static inline void memalloc_noio_restore(unsigned int flags) > > > > > static inline unsigned int memalloc_nofs_save(void) > > > > > { > > > > > unsigned int flags = current->flags & PF_MEMALLOC_NOFS; > > > > > + > > > > > + // just like slab_pre_alloc_hook > > > > > + fs_reclaim_acquire(current->flags & gfp_allowed_mask); > > > > > + fs_reclaim_release(current->flags & gfp_allowed_mask); > > > > > + > > > > > current->flags |= PF_MEMALLOC_NOFS; > > > > > return flags; > > > > > } > > > > > > > > > > > > > > > > The workqueue approach has been good enough so far. Technically there is > > > > > > a higher priority workqueue that this work could be scheduled on, but > > > > > > save for this miss on my part, the system workqueue has worked out fine. > > > > > > > > > > > In the future as I mentioned above. It would be good to support actually > > > > > > getting pages, but it's work that needs to be tackled with a bit of > > > > > > care. I might target the work for v5.14. > > > > > > > > > > > > > this is our application pipeline. > > > > > > > file_pre_process | > > > > > > > bwa.nipt xx | > > > > > > > samtools.nipt sort xx | > > > > > > > file_post_process > > > > > > > > > > > > > > file_pre_process/file_post_process is fast, so often are blocked by > > > > > > > pipe input/output. > > > > > > > > > > > > > > 'bwa.nipt xx' is a high-cpu-load, almost all of CPU cores. > > > > > > > > > > > > > > 'samtools.nipt sort xx' is a high-mem-load, it keep the input in memory. > > > > > > > if the memory is not enough, it will save all the buffer to temp file, > > > > > > > so it is sometimes high-IO-load too(write 60G or more to file). > > > > > > > > > > > > > > > > > > > > > xfstests(generic/476) is just high-IO-load, cpu/memory load is NOT high. > > > > > > > so xfstests(generic/476) maybe easy than our application pipeline. > > > > > > > > > > > > > > Although there is yet not a simple reproducer for another problem > > > > > > > happend here, but there is a little high chance that something is wrong > > > > > > > in btrfs/mm/fs-buffer. > > > > > > > > but another problem(os freezed without call trace, PANIC without OOPS?, > > > > > > > > the reason is yet unkown) still happen. > > > > > > > > > > > > I do not have an answer for this. I would recommend looking into kdump. > > > > > > > > > > percpu ENOMEM problem blocked many heavy load test a little long time? > > > > > I still guess this problem of system freeze is a mm/btrfs problem. > > > > > OOM not work, OOPS not work too. > > > > > > > > > > > > > I don't follow. Is this still a problem after the patch? > > > > > > > > > After the patch for percpu ENOMEM, the problem of system freeze have a high > > > frequecy (>75%) to be triggered by our user-space application. > > > > > > The problem of system freeze maybe not caused by the percpu ENOMEM patch. > > > > > > percpu ENOMEM problem maybe more easy to happen than the problem of > > > system freeze. > > > > After highmem zone +80% / otherzone +40% of WMARK_MIN/ WMARK_LOW/ > > WMARK_HIGH, we walked around or reduced the reproduce frequency of the > > problem of system freeze. > > > > so this is a problem of linux-mm. > > > > the user case of our user-space application. > > 1) write the files with the total size > 3 * memory size. > > the memory size > 128G > > 2) btrfs with SSD/SAS, SSD/SATA, or btrfs RAID6 hdd > > SSD/NVMe maybe too fast, so difficult to reproduce. > > 3) some CPU load, and some memory load. > > > > To me it just sounds like writeback is slow. It's hard to debug a system > without actually observing it as well. You might want to limit the > memory allotted to the workload cgroup possibly memory.high. This may > help kick reclaim in earlier. It is system panic (but NO OOPS info). some info is outputed to IPMI/dell iDRAC 2 | 04/03/2021 | 11:35:01 | OS Critical Stop #0x46 | Run-time critical stop () | Asserted 3 | Linux kernel panic: Fatal excep 4 | Linux kernel panic: tion Now I use vm.watermark_scale_factor=40 (default 10) to help kick reclaim in earlier, the reproduce frequency is reduced but still >25%. I will start a new mail thread because this is not related to percpu ENOMEM. > > btrfs and other fs seem not like mempool_t wiht pre-alloc, so difficult > > job is left to the system-wide reclaim/pre-alloc of linux-mm. > > > > maye memalloc_nofs_save() or memalloc_nofs_restore() is a good place to > > add some sync/aysnc memory reclaim/pre-alloc operations for WMARK_MIN/ > > WMARK_LOW/WMARK_HIGH and percpu PCPU_EMPTY_POP_PAGES_LOW. > > > > It's not that simple. Memory reclaim is a balancing act and these places > mark where reclaim cannot trigger writeback and thus oom-killer is the > only way out. I'm sorry, but beyond the above, I don't really have any > additional advice besides retuning your workload to use less memory and > give the system more headroom. Thanks for this info. > I appreciate the bug report though and if its anything percpu related I > will always be available. The patch that fixed percpu ENOMEM already helps a lot. Thanks. Best Regards Wang Yugui (wangyugui@e16-tech.com) 2021/04/12