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Tue, 25 May 2021 17:22:01 +0000 Date: Tue, 25 May 2021 10:21:57 -0700 From: Roman Gushchin To: Muchun Song CC: , , , , , , , , , , , Subject: Re: [RFC PATCH v3 03/12] mm: memcontrol: make lruvec lock safe when the LRU pages reparented Message-ID: References: <20210421070059.69361-1-songmuchun@bytedance.com> <20210421070059.69361-4-songmuchun@bytedance.com> Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <20210421070059.69361-4-songmuchun@bytedance.com> X-Originating-IP: [2620:10d:c090:400::5:5cc2] X-ClientProxiedBy: MWHPR12CA0034.namprd12.prod.outlook.com (2603:10b6:301:2::20) To BYAPR15MB4136.namprd15.prod.outlook.com (2603:10b6:a03:96::24) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from carbon.dhcp.thefacebook.com (2620:10d:c090:400::5:5cc2) by MWHPR12CA0034.namprd12.prod.outlook.com (2603:10b6:301:2::20) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.4150.24 via Frontend Transport; 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dkim=pass header.d=fb.com header.s=facebook header.b=VXh1eeZo; dmarc=pass (policy=reject) header.from=fb.com; spf=pass (imf08.hostedemail.com: domain of "prvs=477960a1d1=guro@fb.com" designates 67.231.153.30 as permitted sender) smtp.mailfrom="prvs=477960a1d1=guro@fb.com" X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 400F480234A3 X-Stat-Signature: ycxp19murdujfjifkdpexk9fybnkqgo6 X-HE-Tag: 1621963324-215082 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 Wed, Apr 21, 2021 at 03:00:50PM +0800, Muchun Song wrote: > The diagram below shows how to make the page lruvec lock safe when the > LRU pages reparented. > > lock_page_lruvec(page) > retry: > lruvec = mem_cgroup_page_lruvec(page); > > // The page is reparented at this time. > spin_lock(&lruvec->lru_lock); > > if (unlikely(lruvec_memcg(lruvec) != page_memcg(page))) > // Acquired the wrong lruvec lock and need to retry. > // Because this page is on the parent memcg lruvec list. > goto retry; > > // If we reach here, it means that page_memcg(page) is stable. > > memcg_reparent_objcgs(memcg) > // lruvec belongs to memcg and lruvec_parent belongs to parent memcg. > spin_lock(&lruvec->lru_lock); > spin_lock(&lruvec_parent->lru_lock); > > // Move all the pages from the lruvec list to the parent lruvec list. > > spin_unlock(&lruvec_parent->lru_lock); > spin_unlock(&lruvec->lru_lock); > > After we acquire the lruvec lock, we need to check whether the page is > reparented. If so, we need to reacquire the new lruvec lock. On the > routine of the LRU pages reparenting, we will also acquire the lruvec > lock (Will be implemented in the later patch). So page_memcg() cannot > be changed when we hold the lruvec lock. > > Since lruvec_memcg(lruvec) is always equal to page_memcg(page) after > we hold the lruvec lock, lruvec_memcg_debug() check is pointless. So > remove it. > > This is a preparation for reparenting the LRU pages. > > Signed-off-by: Muchun Song Acked-by: Roman Gushchin Thanks!