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Tue, 17 Aug 2021 21:28:40 -0700 (PDT) MIME-Version: 1.0 References: <20210814052519.86679-1-songmuchun@bytedance.com> <20210814052519.86679-4-songmuchun@bytedance.com> In-Reply-To: From: Muchun Song Date: Wed, 18 Aug 2021 12:28:02 +0800 Message-ID: Subject: Re: [PATCH v1 03/12] mm: memcontrol: make lruvec lock safe when LRU pages are reparented To: Roman Gushchin Cc: Johannes Weiner , Michal Hocko , Andrew Morton , Shakeel Butt , Vladimir Davydov , LKML , Linux Memory Management List , Xiongchun duan , fam.zheng@bytedance.com, "Singh, Balbir" , Yang Shi , Alex Shi , Muchun Song , Qi Zheng Content-Type: text/plain; charset="UTF-8" Authentication-Results: imf26.hostedemail.com; dkim=pass header.d=bytedance-com.20150623.gappssmtp.com header.s=20150623 header.b=YGtvo4t4; dmarc=pass (policy=none) header.from=bytedance.com; spf=pass (imf26.hostedemail.com: domain of songmuchun@bytedance.com designates 209.85.215.181 as permitted sender) smtp.mailfrom=songmuchun@bytedance.com X-Stat-Signature: wsq6nf8pbnx8c9pt7mkiuqgqwbq8mihz X-Rspamd-Queue-Id: A975F20061D8 X-Rspamd-Server: rspam05 X-HE-Tag: 1629260921-280885 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, Aug 18, 2021 at 11:18 AM Roman Gushchin wrote: > > 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. Got it. I'll drop all acks in the next version. Thanks. > > Thanks!