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=-5.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 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 3831EC7618B for ; Wed, 24 Jul 2019 06:27:32 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id ED6C1229F3 for ; Wed, 24 Jul 2019 06:27:31 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1563949652; bh=9dMf+7r227Y03NWApAtcyWQAesltuPtcVGhKQt5I60o=; h=Date:From:To:Subject:References:In-Reply-To:List-ID:From; b=rqVsupQAQ5ffwWs3Ov64/puz7BsOzLCqnTOtwp5waUerzySD9KwDpm7HNFcxwHxAA tEGus2xlXggOnHP9/xJsU+R25w6B+j0CDsPTvZvElRQcI/TxK+CniiEwpc4d8ZmBWn fXNhYRjGo0s9b14jFxZu+TdR8t4wKWHEF3VA7dX8= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726026AbfGXG1a (ORCPT ); Wed, 24 Jul 2019 02:27:30 -0400 Received: from mx2.suse.de ([195.135.220.15]:39774 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1725882AbfGXG1a (ORCPT ); Wed, 24 Jul 2019 02:27:30 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 22667AC94 for ; Wed, 24 Jul 2019 06:27:28 +0000 (UTC) Date: Wed, 24 Jul 2019 08:27:27 +0200 From: Michal Hocko To: linux-kernel@vger.kernel.org Subject: Re: + mm-oom-avoid-printk-iteration-under-rcu.patch added to -mm tree Message-ID: <20190724062727.GA10882@dhcp22.suse.cz> References: <20190723231429.b0bmJ%akpm@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190723231429.b0bmJ%akpm@linux-foundation.org> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Andrew, I've had some concerns wrt. this patch - especially the additional complexity - and I have to say I am not convinced that this is really needed. Our past experience in this area suggests that more tricky code leads to different corner cases. So I am really reluctant to add more complexity without any real world reports. On Tue 23-07-19 16:14:29, Andrew Morton wrote: > From: Tetsuo Handa > Subject: mm, oom: avoid printk() iteration under RCU > > Currently dump_tasks() might call printk() for many thousands times under > RCU, which might take many minutes for slow consoles. Therefore, split > dump_tasks() into three stages; take a snapshot of possible OOM victim > candidates under RCU, dump the snapshot from reschedulable context, and > destroy the snapshot. > > In a future patch, the first stage would be moved to select_bad_process() > and the third stage would be moved to after oom_kill_process(), and will > simplify refcount handling. > > Link: http://lkml.kernel.org/r/1563360901-8277-1-git-send-email-penguin-kernel@I-love.SAKURA.ne.jp > Signed-off-by: Tetsuo Handa > Cc: Shakeel Butt > Cc: Michal Hocko > Cc: Roman Gushchin > Cc: David Rientjes > Signed-off-by: Andrew Morton > --- > > include/linux/sched.h | 1 > mm/oom_kill.c | 67 +++++++++++++++++++--------------------- > 2 files changed, 34 insertions(+), 34 deletions(-) > > --- a/include/linux/sched.h~mm-oom-avoid-printk-iteration-under-rcu > +++ a/include/linux/sched.h > @@ -1246,6 +1246,7 @@ struct task_struct { > #ifdef CONFIG_MMU > struct task_struct *oom_reaper_list; > #endif > + struct list_head oom_victim_list; > #ifdef CONFIG_VMAP_STACK > struct vm_struct *stack_vm_area; > #endif > --- a/mm/oom_kill.c~mm-oom-avoid-printk-iteration-under-rcu > +++ a/mm/oom_kill.c > @@ -377,36 +377,13 @@ static void select_bad_process(struct oo > } > } > > -static int dump_task(struct task_struct *p, void *arg) > -{ > - struct oom_control *oc = arg; > - struct task_struct *task; > - > - if (oom_unkillable_task(p)) > - return 0; > > - /* p may not have freeable memory in nodemask */ > - if (!is_memcg_oom(oc) && !oom_cpuset_eligible(p, oc)) > - return 0; > - > - task = find_lock_task_mm(p); > - if (!task) { > - /* > - * This is a kthread or all of p's threads have already > - * detached their mm's. There's no need to report > - * them; they can't be oom killed anyway. > - */ > - return 0; > +static int add_candidate_task(struct task_struct *p, void *arg) > +{ > + if (!oom_unkillable_task(p)) { > + get_task_struct(p); > + list_add_tail(&p->oom_victim_list, (struct list_head *) arg); > } > - > - pr_info("[%7d] %5d %5d %8lu %8lu %8ld %8lu %5hd %s\n", > - task->pid, from_kuid(&init_user_ns, task_uid(task)), > - task->tgid, task->mm->total_vm, get_mm_rss(task->mm), > - mm_pgtables_bytes(task->mm), > - get_mm_counter(task->mm, MM_SWAPENTS), > - task->signal->oom_score_adj, task->comm); > - task_unlock(task); > - > return 0; > } > > @@ -422,19 +399,41 @@ static int dump_task(struct task_struct > */ > static void dump_tasks(struct oom_control *oc) > { > - pr_info("Tasks state (memory values in pages):\n"); > - pr_info("[ pid ] uid tgid total_vm rss pgtables_bytes swapents oom_score_adj name\n"); > + static LIST_HEAD(list); > + struct task_struct *p; > + struct task_struct *t; > > if (is_memcg_oom(oc)) > - mem_cgroup_scan_tasks(oc->memcg, dump_task, oc); > + mem_cgroup_scan_tasks(oc->memcg, add_candidate_task, &list); > else { > - struct task_struct *p; > - > rcu_read_lock(); > for_each_process(p) > - dump_task(p, oc); > + add_candidate_task(p, &list); > rcu_read_unlock(); > } > + pr_info("Tasks state (memory values in pages):\n"); > + pr_info("[ pid ] uid tgid total_vm rss pgtables_bytes swapents oom_score_adj name\n"); > + list_for_each_entry(p, &list, oom_victim_list) { > + cond_resched(); > + /* p may not have freeable memory in nodemask */ > + if (!is_memcg_oom(oc) && !oom_cpuset_eligible(p, oc)) > + continue; > + /* All of p's threads might have already detached their mm's. */ > + t = find_lock_task_mm(p); > + if (!t) > + continue; > + pr_info("[%7d] %5d %5d %8lu %8lu %8ld %8lu %5hd %s\n", > + t->pid, from_kuid(&init_user_ns, task_uid(t)), > + t->tgid, t->mm->total_vm, get_mm_rss(t->mm), > + mm_pgtables_bytes(t->mm), > + get_mm_counter(t->mm, MM_SWAPENTS), > + t->signal->oom_score_adj, t->comm); > + task_unlock(t); > + } > + list_for_each_entry_safe(p, t, &list, oom_victim_list) { > + list_del(&p->oom_victim_list); > + put_task_struct(p); > + } > } > > static void dump_oom_summary(struct oom_control *oc, struct task_struct *victim) > _ > > Patches currently in -mm which might be from penguin-kernel@I-love.SAKURA.ne.jp are > > mm-oom-avoid-printk-iteration-under-rcu.patch > info-task-hung-in-generic_file_write_iter.patch > info-task-hung-in-generic_file_write-fix.patch > kexec-bail-out-upon-sigkill-when-allocating-memory.patch -- Michal Hocko SUSE Labs