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Fri, 10 Jan 2020 11:49:08 +0300 (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits)) (Client certificate not present) Subject: Re: [PATCH v7 02/10] mm/memcg: fold lru_lock in lock_page_lru To: Alex Shi , cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, akpm@linux-foundation.org, mgorman@techsingularity.net, tj@kernel.org, hughd@google.com, daniel.m.jordan@oracle.com, yang.shi@linux.alibaba.com, willy@infradead.org, shakeelb@google.com, hannes@cmpxchg.org Cc: Michal Hocko , Vladimir Davydov References: <1577264666-246071-1-git-send-email-alex.shi@linux.alibaba.com> <1577264666-246071-3-git-send-email-alex.shi@linux.alibaba.com> From: Konstantin Khlebnikov Message-ID: <36d7e390-a3d1-908c-d181-4a9e9c8d3d98@yandex-team.ru> Date: Fri, 10 Jan 2020 11:49:08 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.2.2 MIME-Version: 1.0 In-Reply-To: <1577264666-246071-3-git-send-email-alex.shi@linux.alibaba.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-CA Content-Transfer-Encoding: 7bit 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 25/12/2019 12.04, Alex Shi wrote: > From the commit_charge's explanations and mem_cgroup_commit_charge > comments, as well as call path when lrucare is ture, The lru_lock is > just to guard the task migration(which would be lead to move_account) > So it isn't needed when !PageLRU, and better be fold into PageLRU to > reduce lock contentions. > > Signed-off-by: Alex Shi > Cc: Johannes Weiner > Cc: Michal Hocko > Cc: Matthew Wilcox > Cc: Vladimir Davydov > Cc: Andrew Morton > Cc: cgroups@vger.kernel.org > Cc: linux-mm@kvack.org > Cc: linux-kernel@vger.kernel.org > --- > mm/memcontrol.c | 9 ++++----- > 1 file changed, 4 insertions(+), 5 deletions(-) > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index c5b5f74cfd4d..0ad10caabc3d 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -2572,12 +2572,11 @@ static void cancel_charge(struct mem_cgroup *memcg, unsigned int nr_pages) > > static void lock_page_lru(struct page *page, int *isolated) > { > - pg_data_t *pgdat = page_pgdat(page); > - > - spin_lock_irq(&pgdat->lru_lock); > if (PageLRU(page)) { > + pg_data_t *pgdat = page_pgdat(page); > struct lruvec *lruvec; > > + spin_lock_irq(&pgdat->lru_lock); That's wrong. Here PageLRU must be checked again under lru_lock. Also I don't like these functions: - called lock/unlock but actually also isolates - used just once - pgdat evaluated twice > lruvec = mem_cgroup_page_lruvec(page, pgdat); > ClearPageLRU(page); > del_page_from_lru_list(page, lruvec, page_lru(page)); > @@ -2588,17 +2587,17 @@ static void lock_page_lru(struct page *page, int *isolated) > > static void unlock_page_lru(struct page *page, int isolated) > { > - pg_data_t *pgdat = page_pgdat(page); > > if (isolated) { > + pg_data_t *pgdat = page_pgdat(page); > struct lruvec *lruvec; > > lruvec = mem_cgroup_page_lruvec(page, pgdat); > VM_BUG_ON_PAGE(PageLRU(page), page); > SetPageLRU(page); > add_page_to_lru_list(page, lruvec, page_lru(page)); > + spin_unlock_irq(&pgdat->lru_lock); > } > - spin_unlock_irq(&pgdat->lru_lock); > } > > static void commit_charge(struct page *page, struct mem_cgroup *memcg, >