From patchwork Fri Apr 16 05:14:01 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Muchun Song X-Patchwork-Id: 12206699 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=-16.5 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,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 B1F09C433B4 for ; Fri, 16 Apr 2021 05:15:51 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 2E7336113B for ; Fri, 16 Apr 2021 05:15:51 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 2E7336113B Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=bytedance.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id A87556B006C; Fri, 16 Apr 2021 01:15:50 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id A358D6B0071; Fri, 16 Apr 2021 01:15:50 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 8FFD26B0072; Fri, 16 Apr 2021 01:15:50 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0112.hostedemail.com [216.40.44.112]) by kanga.kvack.org (Postfix) with ESMTP id 696316B006C for ; Fri, 16 Apr 2021 01:15:50 -0400 (EDT) Received: from smtpin17.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with ESMTP id 31DFE5848 for ; Fri, 16 Apr 2021 05:15:50 +0000 (UTC) X-FDA: 78037068060.17.B2EEEE6 Received: from mail-pj1-f41.google.com (mail-pj1-f41.google.com [209.85.216.41]) by imf24.hostedemail.com (Postfix) with ESMTP id 3D7A5A00038C for ; Fri, 16 Apr 2021 05:15:43 +0000 (UTC) Received: by mail-pj1-f41.google.com with SMTP id r13so9526273pjf.2 for ; Thu, 15 Apr 2021 22:15:49 -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=x3mRR8adpG+SIPQvbajyUHRAzVYGQ9kXgMEs7JE0sm5iBBYsM7za2rneJ2x+zx7Alm nvjA0ySFpVE0MWfbuJUl+trTsqrxpnkGXWgmQ1htfWCvNWccRgTDGYGaEs7Feyw4sZ41 Nyo0Z2ol/a0h+wdqzCXC58YJtzlmXejXT0oumYu+JvdMKtxzxN6FdzbxwmbUg8/S9Eap H4ZZve05NA7mvYp2zP0e740L9pte8vGxHJ68iJKbrfp6Xk5BJVu0G0bgdZWFZhcNG0MR WAdfx26I8k/nlMtz6X2Uhe00xyCK4COeU4jU9z0DBaM4bXqoCGlrnT/S13+W2n51u6bb wnPQ== 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=BLqsrgwzGPbOy3Dq67PZMNVyil+8j1ufweIJ5e4yHXnrrjz+d7tzMASURTbkgM9Flh GcWdoSJ+jKETpiBIMFWWctp9RWX+jfuokmYvbIL+7IkvlqUp6JMiPxpwb6XqtjVH7osc QqMLP2otnU/XluG9exjGVpOHAi/nS6t4nK5VJz83jDIjvh0SrlMFQBr6tUfk2c5M6/Ru tIL2kp2DoC4rPp0niRIdMlKrdKQBMB810Jhtm3nyDQwaRGaTEYDmWORxw3Ydk+c41dUv /b9BkVudC8W5mDUUnPTlcoMAGTiNyfRrsxQ30kPbnHG77c/b+RJrVK1lRcl3ouf3urP5 B6Hg== X-Gm-Message-State: AOAM533c4UyXMOKKkveY2ZCD0veUWd5L7WkfcOSSDZ4NggNpqGm2nmK2 8G4Ezct+e+vnQmY2TObaffJeuA== X-Google-Smtp-Source: ABdhPJyRUkfUK1Gz4fhB+MEe5DNop4sWVG+HsPBKJEMPEQLpoPtCsMG3b1+SKM+CihVIFoRzjH8IfQ== X-Received: by 2002:a17:90a:9405:: with SMTP id r5mr8098835pjo.139.1618550148926; Thu, 15 Apr 2021 22:15:48 -0700 (PDT) Received: from localhost.localdomain ([139.177.225.235]) by smtp.gmail.com with ESMTPSA id j7sm3518540pfd.129.2021.04.15.22.15.44 (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Thu, 15 Apr 2021 22:15:48 -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 v2 2/8] mm: memcontrol: bail out early when !mm in get_mem_cgroup_from_mm Date: Fri, 16 Apr 2021 13:14:01 +0800 Message-Id: <20210416051407.54878-3-songmuchun@bytedance.com> X-Mailer: git-send-email 2.21.0 (Apple Git-122) In-Reply-To: <20210416051407.54878-1-songmuchun@bytedance.com> References: <20210416051407.54878-1-songmuchun@bytedance.com> MIME-Version: 1.0 X-Stat-Signature: sq7axp9xi768sxkqy8ugsqrtw9d84xnw X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 3D7A5A00038C Received-SPF: none (bytedance.com>: No applicable sender policy available) receiver=imf24; identity=mailfrom; envelope-from=""; helo=mail-pj1-f41.google.com; client-ip=209.85.216.41 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1618550143-413218 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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;