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=-16.7 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT 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 B40ACC433ED for ; Sat, 17 Apr 2021 04:38:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 98DB7611AB for ; Sat, 17 Apr 2021 04:38:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232972AbhDQEif (ORCPT ); Sat, 17 Apr 2021 00:38:35 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:60514 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229629AbhDQEie (ORCPT ); Sat, 17 Apr 2021 00:38:34 -0400 Received: from mail-pl1-x62a.google.com (mail-pl1-x62a.google.com [IPv6:2607:f8b0:4864:20::62a]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 74092C061574 for ; Fri, 16 Apr 2021 21:38:08 -0700 (PDT) Received: by mail-pl1-x62a.google.com with SMTP id 20so11050840pll.7 for ; Fri, 16 Apr 2021 21:38:08 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=bytedance-com.20150623.gappssmtp.com; s=20150623; h=from:to:cc:subject:date:message-id:in-reply-to:references :mime-version:content-transfer-encoding; bh=NE/BcoGMuqPyqQGyjWQGMTxC1WpQbz3TqD3QbwUvSZY=; b=HCYBSuWL5lNSfyR1c5D+bsBKj9KEfSpvl6qC9ksYnjL148APwpW4TAUtqKdnJ7pC7A TcpivOKDUXNMLR3P+FWv0R6KBx0FXOHEtaFTOTJjSlGGMEKxleb0kqY6b+3DAzr/+qMO yUn6B0VTyigbyVwQw5NZ3llxK3JzpPsR4mNmCT8d1ttTFw24RIUEdIoPxa7Hr+KPWBxb P8YHj4MA8iPuorRIuQPnQgP4eCAw+CDbYwkVLDQxwWWIhoiTTe8bIpNqwVa1ED87nl6A fW/wJXy4jF0w1hZj+aZIv7N5SUCY68+4Hz3w1OYGvkhz307Khf9vrRxWNo24RfqfKG8A gaRQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references:mime-version:content-transfer-encoding; bh=NE/BcoGMuqPyqQGyjWQGMTxC1WpQbz3TqD3QbwUvSZY=; b=fqaA+gfwBfLavCuqCA3eVzynLMppniRlew8jeYLO1YX8/9+hOIkItiirhCJfLW5Mrq BktJUi4x5d7qpvtoLy1Fx05sRt7V0hEupZ42vHA2eTzClJVwDA2H5kikC2Ou5UznLIKM utwqxjFHF5HWdGJNLMY5t9ViwUv5A8vv5bl1LFv2u0qI9KUOh7q3wVuo7oV+KI8dWkUz PRi88wVQpgSrSwZcgP2rtFJ3S8P/RJ/oxb6YstCGUXSBoby2fZfYBpp/rKG+7dOT49zO WL6yJ7lgC9cPVQAjq07uauVl7wOEBGfR/sqWTOmtsZkNnPjp9iNBmBS0bIrcn27tii5I nzNw== X-Gm-Message-State: AOAM530hZqv0BKbw3rP95IfI1+lLrs+M9HtRN9TX7riQvBw6LaV/6GQ2 5Rhc36hv2Pu0EImtCbNTLgDxoFDfrXFfBw== X-Google-Smtp-Source: ABdhPJzWa9DWpbE9nY7cRes3aa7lKCkPT7KXRZi0kgxvIDJ4A4qJBPj3gK6804vLQ/irrw+KbLogpQ== X-Received: by 2002:a17:902:cec4:b029:e9:58eb:562b with SMTP id d4-20020a170902cec4b02900e958eb562bmr12659796plg.63.1618634288058; Fri, 16 Apr 2021 21:38:08 -0700 (PDT) Received: from localhost.bytedance.net ([139.177.225.228]) by smtp.gmail.com with ESMTPSA id w21sm7064775pjy.21.2021.04.16.21.38.02 (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Fri, 16 Apr 2021 21:38:07 -0700 (PDT) From: Muchun Song To: guro@fb.com, hannes@cmpxchg.org, mhocko@kernel.org, akpm@linux-foundation.org, shakeelb@google.com, vdavydov.dev@gmail.com Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, duanxiongchun@bytedance.com, Muchun Song , Michal Hocko Subject: [PATCH v3 2/8] mm: memcontrol: bail out early when !mm in get_mem_cgroup_from_mm Date: Sat, 17 Apr 2021 12:35:32 +0800 Message-Id: <20210417043538.9793-3-songmuchun@bytedance.com> X-Mailer: git-send-email 2.21.0 (Apple Git-122) In-Reply-To: <20210417043538.9793-1-songmuchun@bytedance.com> References: <20210417043538.9793-1-songmuchun@bytedance.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org When mm is NULL, we do not need to hold rcu lock and call css_tryget for the root memcg. And we also do not need to check !mm in every loop of while. So bail out early when !mm. Signed-off-by: Muchun Song Acked-by: Johannes Weiner Reviewed-by: Shakeel Butt Acked-by: Roman Gushchin Acked-by: Michal Hocko --- mm/memcontrol.c | 25 ++++++++++++++----------- 1 file changed, 14 insertions(+), 11 deletions(-) diff --git a/mm/memcontrol.c b/mm/memcontrol.c index f229de925aa5..50e3cf1e263e 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -901,20 +901,23 @@ struct mem_cgroup *get_mem_cgroup_from_mm(struct mm_struct *mm) if (mem_cgroup_disabled()) return NULL; + /* + * Page cache insertions can happen without an + * actual mm context, e.g. during disk probing + * on boot, loopback IO, acct() writes etc. + * + * No need to css_get on root memcg as the reference + * counting is disabled on the root level in the + * cgroup core. See CSS_NO_REF. + */ + if (unlikely(!mm)) + return root_mem_cgroup; + rcu_read_lock(); do { - /* - * Page cache insertions can happen without an - * actual mm context, e.g. during disk probing - * on boot, loopback IO, acct() writes etc. - */ - if (unlikely(!mm)) + memcg = mem_cgroup_from_task(rcu_dereference(mm->owner)); + if (unlikely(!memcg)) memcg = root_mem_cgroup; - else { - memcg = mem_cgroup_from_task(rcu_dereference(mm->owner)); - if (unlikely(!memcg)) - memcg = root_mem_cgroup; - } } while (!css_tryget(&memcg->css)); rcu_read_unlock(); return memcg; -- 2.11.0