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Received: from IT-FVFX43SYHV2H.local(mailfrom:alex.shi@linux.alibaba.com fp:SMTPD_---0TncLfyC_1578908838) by smtp.aliyun-inc.com(127.0.0.1); Mon, 13 Jan 2020 17:47:19 +0800 Subject: Re: [PATCH v7 02/10] mm/memcg: fold lru_lock in lock_page_lru To: Konstantin Khlebnikov , 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> <36d7e390-a3d1-908c-d181-4a9e9c8d3d98@yandex-team.ru> From: Alex Shi Message-ID: <952d02c2-8aa5-40bb-88bb-c43dee65c8bc@linux.alibaba.com> Date: Mon, 13 Jan 2020 17:45:51 +0800 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:68.0) Gecko/20100101 Thunderbird/68.3.1 MIME-Version: 1.0 In-Reply-To: <36d7e390-a3d1-908c-d181-4a9e9c8d3d98@yandex-team.ru> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable 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: =E5=9C=A8 2020/1/10 =E4=B8=8B=E5=8D=884:49, Konstantin Khlebnikov =E5=86=99= =E9=81=93: > On 25/12/2019 12.04, Alex Shi wrote: >> =C2=A0From the commit_charge's explanations and mem_cgroup_commit_char= ge >> 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 >> --- >> =C2=A0 mm/memcontrol.c | 9 ++++----- >> =C2=A0 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 *m= emcg, unsigned int nr_pages) >> =C2=A0 =C2=A0 static void lock_page_lru(struct page *page, int *isolat= ed) >> =C2=A0 { >> -=C2=A0=C2=A0=C2=A0 pg_data_t *pgdat =3D page_pgdat(page); >> - >> -=C2=A0=C2=A0=C2=A0 spin_lock_irq(&pgdat->lru_lock); >> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 if (PageLRU(page)) { >> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 pg_data_t *pgdat =3D page_= pgdat(page); >> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 struct lruvec *= lruvec; >> =C2=A0 +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 spin_lock_irq(&pgda= t->lru_lock); >=20 > That's wrong. Here PageLRU must be checked again under lru_lock. Hi, Konstantin, For logical remain, we can get the lock and then release for !PageLRU.=20 but I still can figure out the problem scenario. Would like to give more = hints? >=20 >=20 > Also I don't like these functions: > - called lock/unlock but actually also isolates > - used just once > - pgdat evaluated twice That's right. I will fold these functions into commit_charge. Thanks Alex