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Wed, 18 Aug 2021 03:18:05 +0000 Date: Tue, 17 Aug 2021 20:18:01 -0700 From: Roman Gushchin To: Muchun Song CC: , , , , , , , , , , , , , Subject: Re: [PATCH v1 03/12] mm: memcontrol: make lruvec lock safe when LRU pages are reparented Message-ID: References: <20210814052519.86679-1-songmuchun@bytedance.com> <20210814052519.86679-4-songmuchun@bytedance.com> Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <20210814052519.86679-4-songmuchun@bytedance.com> X-ClientProxiedBy: MWHPR17CA0091.namprd17.prod.outlook.com (2603:10b6:300:c2::29) 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::5:20bf) by MWHPR17CA0091.namprd17.prod.outlook.com (2603:10b6:300:c2::29) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.4436.19 via Frontend Transport; Wed, 18 Aug 2021 03:18:04 +0000 X-MS-PublicTrafficType: Email X-MS-Office365-Filtering-Correlation-Id: bc0011ef-d572-4b42-14a3-08d961f6cbaa X-MS-TrafficTypeDiagnostic: BYAPR15MB3078: X-Microsoft-Antispam-PRVS: X-FB-Source: Internal X-MS-Oob-TLC-OOBClassifiers: OLM:10000; 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dkim=pass header.d=fb.com header.s=facebook header.b=OJFtoWsF; spf=pass (imf30.hostedemail.com: domain of "prvs=786498ca91=guro@fb.com" designates 67.231.153.30 as permitted sender) smtp.mailfrom="prvs=786498ca91=guro@fb.com"; dmarc=pass (policy=reject) header.from=fb.com X-Rspamd-Server: rspam01 X-Stat-Signature: itwt17ga9jkw78dkuo11e9radbdsy5fg X-HE-Tag: 1629256693-406808 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 Sat, Aug 14, 2021 at 01:25:10PM +0800, Muchun Song wrote: > The diagram below shows how to make the folio lruvec lock safe when LRU > pages are reparented. > > folio_lruvec_lock(folio) > retry: > lruvec = folio_lruvec(folio); > > // The folio is reparented at this time. > spin_lock(&lruvec->lru_lock); > > if (unlikely(lruvec_memcg(lruvec) != folio_memcg(folio))) > // Acquired the wrong lruvec lock and need to retry. > // Because this folio is on the parent memcg lruvec list. > goto retry; > > // If we reach here, it means that folio_memcg(folio) 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 folio 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 folio_memcg() cannot > be changed when we hold the lruvec lock. > > Since lruvec_memcg(lruvec) is always equal to folio_memcg(folio) 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 Maybe it's mostly s/page/folio, but the patch looks quite differently in comparison to the version I did ack. In general, please, drop acks when there are significant changes between versions. Thanks!