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=-15.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 44312C433E0 for ; Wed, 10 Feb 2021 09:18:33 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 9AEBC64DD5 for ; Wed, 10 Feb 2021 09:18:32 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 9AEBC64DD5 Authentication-Results: mail.kernel.org; dmarc=fail (p=quarantine dis=none) header.from=suse.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 0303F6B0006; Wed, 10 Feb 2021 04:18:32 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id F23E46B006C; Wed, 10 Feb 2021 04:18:31 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id DEBD96B006E; Wed, 10 Feb 2021 04:18:31 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0013.hostedemail.com [216.40.44.13]) by kanga.kvack.org (Postfix) with ESMTP id C9FA06B0006 for ; Wed, 10 Feb 2021 04:18:31 -0500 (EST) Received: from smtpin20.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with ESMTP id 95191180515C1 for ; Wed, 10 Feb 2021 09:18:31 +0000 (UTC) X-FDA: 77801807622.20.76578D4 Received: from mx2.suse.de (mx2.suse.de [195.135.220.15]) by imf16.hostedemail.com (Postfix) with ESMTP id 4A64280191EF for ; Wed, 10 Feb 2021 09:18:30 +0000 (UTC) X-Virus-Scanned: by amavisd-new at test-mx.suse.de DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1612948709; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=ASj2m7GT07IQH1F8g5mMfrRhbhZLOXHsiTlFLSHPhQs=; b=IhNDtf/K8be4ssN5h3aEtbjD7q1P9y2RTK5JYLMDrdSoFCLe5AU2rSwLOfTw86//DhosMy n7z4EDkqtrZkJVswhdgEO9Sk6ZnqtjKhUhkhTdLr/VsK9c/u/KMkNjgtavvKrQ9u5a6WLZ QDiZ2U6LnZHJF8LmGEZb/Z7BO93S+ag= Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id AF47EB13F; Wed, 10 Feb 2021 09:18:29 +0000 (UTC) Date: Wed, 10 Feb 2021 10:18:27 +0100 From: Michal Hocko To: Johannes Weiner Cc: Andrew Morton , Muchun Song , Shakeel Butt , linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-team@fb.com Subject: Re: [PATCH] fs: buffer: use raw page_memcg() on locked page Message-ID: References: <20210209190126.97842-1-hannes@cmpxchg.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210209190126.97842-1-hannes@cmpxchg.org> X-Stat-Signature: pz3dmat1p91n395365woyfwj7ykoe9ax X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 4A64280191EF Received-SPF: none (suse.com>: No applicable sender policy available) receiver=imf16; identity=mailfrom; envelope-from=""; helo=mx2.suse.de; client-ip=195.135.220.15 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1612948710-447492 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: On Tue 09-02-21 14:01:26, Johannes Weiner wrote: > alloc_page_buffers() currently uses get_mem_cgroup_from_page() for > charging the buffers to the page owner, which does an rcu-protected > page->memcg lookup and acquires a reference. But buffer allocation has > the page lock held throughout, which pins the page to the memcg and > thereby the memcg - neither rcu nor holding an extra reference during > the allocation are necessary. Use a raw page_memcg() instead. > > This was the last user of get_mem_cgroup_from_page(), delete it. > > Reported-by: Muchun Song > Signed-off-by: Johannes Weiner Acked-by: Michal Hocko Thanks! > --- > fs/buffer.c | 4 ++-- > include/linux/memcontrol.h | 7 ------- > mm/memcontrol.c | 23 ----------------------- > 3 files changed, 2 insertions(+), 32 deletions(-) > > diff --git a/fs/buffer.c b/fs/buffer.c > index 96c7604f69b3..dc5d3e22c493 100644 > --- a/fs/buffer.c > +++ b/fs/buffer.c > @@ -847,7 +847,8 @@ struct buffer_head *alloc_page_buffers(struct page *page, unsigned long size, > if (retry) > gfp |= __GFP_NOFAIL; > > - memcg = get_mem_cgroup_from_page(page); > + /* The page lock pins the memcg */ > + memcg = page_memcg(page); > old_memcg = set_active_memcg(memcg); > > head = NULL; > @@ -868,7 +869,6 @@ struct buffer_head *alloc_page_buffers(struct page *page, unsigned long size, > } > out: > set_active_memcg(old_memcg); > - mem_cgroup_put(memcg); > return head; > /* > * In case anything failed, we just free everything we got. > diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h > index a8c7a0ccc759..a44b2d51aecc 100644 > --- a/include/linux/memcontrol.h > +++ b/include/linux/memcontrol.h > @@ -687,8 +687,6 @@ struct mem_cgroup *mem_cgroup_from_task(struct task_struct *p); > > struct mem_cgroup *get_mem_cgroup_from_mm(struct mm_struct *mm); > > -struct mem_cgroup *get_mem_cgroup_from_page(struct page *page); > - > struct lruvec *lock_page_lruvec(struct page *page); > struct lruvec *lock_page_lruvec_irq(struct page *page); > struct lruvec *lock_page_lruvec_irqsave(struct page *page, > @@ -1169,11 +1167,6 @@ static inline struct mem_cgroup *get_mem_cgroup_from_mm(struct mm_struct *mm) > return NULL; > } > > -static inline struct mem_cgroup *get_mem_cgroup_from_page(struct page *page) > -{ > - return NULL; > -} > - > static inline void mem_cgroup_put(struct mem_cgroup *memcg) > { > } > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index 51778fa9b462..9e455815fb7a 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -1048,29 +1048,6 @@ struct mem_cgroup *get_mem_cgroup_from_mm(struct mm_struct *mm) > } > EXPORT_SYMBOL(get_mem_cgroup_from_mm); > > -/** > - * get_mem_cgroup_from_page: Obtain a reference on given page's memcg. > - * @page: page from which memcg should be extracted. > - * > - * Obtain a reference on page->memcg and returns it if successful. Otherwise > - * root_mem_cgroup is returned. > - */ > -struct mem_cgroup *get_mem_cgroup_from_page(struct page *page) > -{ > - struct mem_cgroup *memcg = page_memcg(page); > - > - if (mem_cgroup_disabled()) > - return NULL; > - > - rcu_read_lock(); > - /* Page should not get uncharged and freed memcg under us. */ > - if (!memcg || WARN_ON_ONCE(!css_tryget(&memcg->css))) > - memcg = root_mem_cgroup; > - rcu_read_unlock(); > - return memcg; > -} > -EXPORT_SYMBOL(get_mem_cgroup_from_page); > - > static __always_inline struct mem_cgroup *active_memcg(void) > { > if (in_interrupt()) > -- > 2.30.0 -- Michal Hocko SUSE Labs