From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-it1-f199.google.com (mail-it1-f199.google.com [209.85.166.199]) by kanga.kvack.org (Postfix) with ESMTP id E8D8F8E0002 for ; Sat, 12 Jan 2019 05:53:10 -0500 (EST) Received: by mail-it1-f199.google.com with SMTP id p21so4840915itb.8 for ; Sat, 12 Jan 2019 02:53:10 -0800 (PST) Received: from www262.sakura.ne.jp (www262.sakura.ne.jp. [202.181.97.72]) by mx.google.com with ESMTPS id e8si1442005jaj.17.2019.01.12.02.53.08 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Sat, 12 Jan 2019 02:53:09 -0800 (PST) Subject: Re: [PATCH 0/2] oom, memcg: do not report racy no-eligible OOM References: <20190109120212.GT31793@dhcp22.suse.cz> <201901102359.x0ANxIbn020225@www262.sakura.ne.jp> <20190111113354.GD14956@dhcp22.suse.cz> <0d67b389-91e2-18ab-b596-39361b895c89@i-love.sakura.ne.jp> <20190111133401.GA6997@dhcp22.suse.cz> <20190111150703.GI14956@dhcp22.suse.cz> <20190111164536.GJ14956@dhcp22.suse.cz> From: Tetsuo Handa Message-ID: <0aacad13-3e91-646a-90b1-c70993b05701@i-love.sakura.ne.jp> Date: Sat, 12 Jan 2019 19:52:50 +0900 MIME-Version: 1.0 In-Reply-To: <20190111164536.GJ14956@dhcp22.suse.cz> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko Cc: Andrew Morton , linux-mm@kvack.org, Johannes Weiner , LKML On 2019/01/12 1:45, Michal Hocko wrote: >>> Anyway, could you update your patch and abstract >>> if (unlikely(tsk_is_oom_victim(current) || >>> fatal_signal_pending(current) || >>> current->flags & PF_EXITING)) >>> >>> in try_charge and reuse it in mem_cgroup_out_of_memory under the >>> oom_lock with an explanation please? >> >> I don't think doing so makes sense, for >> >> tsk_is_oom_victim(current) = T && fatal_signal_pending(current) == F >> >> can't happen for mem_cgroup_out_of_memory() under the oom_lock, and >> current->flags cannot get PF_EXITING when current is inside >> mem_cgroup_out_of_memory(). fatal_signal_pending(current) alone is >> appropriate for mem_cgroup_out_of_memory() under the oom_lock because >> >> tsk_is_oom_victim(current) = F && fatal_signal_pending(current) == T >> >> can happen there. > > I meant to use the same check consistently. If we can bypass the charge > under a list of conditions in the charge path we should be surely be > able to the the same for the oom path. I will not insist but unless > there is a strong reason I would prefer that. > You mean something like this? I'm not sure this change is safe. mm/memcontrol.c | 27 +++++++++++++++++++++++---- 1 file changed, 23 insertions(+), 4 deletions(-) diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 17189da..1733d019 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -248,6 +248,12 @@ enum res_type { iter != NULL; \ iter = mem_cgroup_iter(NULL, iter, NULL)) +static inline bool can_ignore_limit(void) +{ + return tsk_is_oom_victim(current) || fatal_signal_pending(current) || + (current->flags & PF_EXITING); +} + /* Some nice accessors for the vmpressure. */ struct vmpressure *memcg_to_vmpressure(struct mem_cgroup *memcg) { @@ -1395,7 +1401,7 @@ static bool mem_cgroup_out_of_memory(struct mem_cgroup *memcg, gfp_t gfp_mask, * A few threads which were not waiting at mutex_lock_killable() can * fail to bail out. Therefore, check again after holding oom_lock. */ - ret = fatal_signal_pending(current) || out_of_memory(&oc); + ret = can_ignore_limit() || out_of_memory(&oc); mutex_unlock(&oom_lock); return ret; } @@ -1724,6 +1730,10 @@ static enum oom_status mem_cgroup_oom(struct mem_cgroup *memcg, gfp_t mask, int mem_cgroup_unmark_under_oom(memcg); if (mem_cgroup_out_of_memory(memcg, mask, order)) + /* + * Returning OOM_SUCCESS upon can_ignore_limit() is OK, for + * the caller will check can_ignore_limit() again. + */ ret = OOM_SUCCESS; else ret = OOM_FAILED; @@ -1783,6 +1793,11 @@ bool mem_cgroup_oom_synchronize(bool handle) finish_wait(&memcg_oom_waitq, &owait.wait); mem_cgroup_out_of_memory(memcg, current->memcg_oom_gfp_mask, current->memcg_oom_order); + /* + * Returning upon can_ignore_limit() is OK, for the caller is + * already killed... CheckMe: Is this assumption correct? + * Page fault can't happen after getting PF_EXITING? + */ } else { schedule(); mem_cgroup_unmark_under_oom(memcg); @@ -2215,9 +2230,7 @@ static int try_charge(struct mem_cgroup *memcg, gfp_t gfp_mask, * bypass the last charges so that they can exit quickly and * free their memory. */ - if (unlikely(tsk_is_oom_victim(current) || - fatal_signal_pending(current) || - current->flags & PF_EXITING)) + if (unlikely(can_ignore_limit())) goto force; /* @@ -5527,6 +5540,12 @@ static ssize_t memory_max_write(struct kernfs_open_file *of, memcg_memory_event(memcg, MEMCG_OOM); if (!mem_cgroup_out_of_memory(memcg, GFP_KERNEL, 0)) break; + /* + * There is no need to check can_ignore_limit() here, for + * signal_pending(current) above will break anyway. + */ + if (unlikely(can_ignore_limit())) + break; } memcg_wb_domain_size_changed(memcg); -- 1.8.3.1