From: Alex Shi <alex.shi@linux.alibaba.com>
To: Johannes Weiner <hannes@cmpxchg.org>
Cc: 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,
khlebnikov@yandex-team.ru, daniel.m.jordan@oracle.com,
yang.shi@linux.alibaba.com, willy@infradead.org,
"Michal Hocko" <mhocko@kernel.org>,
"Vladimir Davydov" <vdavydov.dev@gmail.com>,
"Roman Gushchin" <guro@fb.com>,
"Shakeel Butt" <shakeelb@google.com>,
"Chris Down" <chris@chrisdown.name>,
"Thomas Gleixner" <tglx@linutronix.de>,
"Vlastimil Babka" <vbabka@suse.cz>, "Qian Cai" <cai@lca.pw>,
"Andrey Ryabinin" <aryabinin@virtuozzo.com>,
"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
"Jérôme Glisse" <jglisse@redhat.com>,
"Andrea Arcangeli" <aarcange@redhat.com>,
"David Rientjes" <rientjes@google.com>,
"Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>,
swkhack <swkhack@gmail.com>,
"Potyra, Stefan" <Stefan.Potyra@elektrobit.com>,
"Mike Rapoport" <rppt@linux.vnet.ibm.com>,
"Stephen Rothwell" <sfr@canb.auug.org.au>,
"Colin Ian King" <colin.king@canonical.com>,
"Jason Gunthorpe" <jgg@ziepe.ca>,
"Mauro Carvalho Chehab" <mchehab+samsung@kernel.org>,
"Peng Fan" <peng.fan@nxp.com>,
"Nikolay Borisov" <nborisov@suse.com>,
"Ira Weiny" <ira.weiny@intel.com>,
"Kirill Tkhai" <ktkhai@virtuozzo.com>,
"Yafang Shao" <laoar.shao@gmail.com>
Subject: Re: [PATCH v3 3/7] mm/lru: replace pgdat lru_lock with lruvec lock
Date: Tue, 19 Nov 2019 18:04:35 +0800 [thread overview]
Message-ID: <85702d50-daf0-ece8-9a5d-e4b860ef2f99@linux.alibaba.com> (raw)
In-Reply-To: <20191118161126.GB365174@cmpxchg.org>
在 2019/11/19 上午12:11, Johannes Weiner 写道:
> On Sat, Nov 16, 2019 at 11:15:02AM +0800, Alex Shi wrote:
>> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
>> index 62470325f9bc..cf274739e619 100644
>> --- a/mm/memcontrol.c
>> +++ b/mm/memcontrol.c
>> @@ -1246,6 +1246,42 @@ struct lruvec *mem_cgroup_page_lruvec(struct page *page, struct pglist_data *pgd
>> return lruvec;
>> }
>>
>> +struct lruvec *lock_page_lruvec_irq(struct page *page,
>> + struct pglist_data *pgdat)
>> +{
>> + struct lruvec *lruvec;
>> +
>> +again:
>> + lruvec = mem_cgroup_page_lruvec(page, pgdat);
>> + spin_lock_irq(&lruvec->lru_lock);
>
> This isn't safe. Nothing prevents the page from being moved to a
> different memcg in between these two operations, and the lruvec having
> been freed by the time you try to acquire the spinlock.
>
> You need to use the rcu lock to dereference page->mem_cgroup and its
> lruvec when coming from the page like this.
Hi Johannes,
Yes, you are right. Thank a lot to point out this!
Could we use rcu lock to guard the lruvec till lruvec->lru_lock getten?
+struct lruvec *lock_page_lruvec_irq(struct page *page,
+ struct pglist_data *pgdat)
+{
+ struct lruvec *lruvec;
+
+again:
+ rcu_read_lock();
+ lruvec = mem_cgroup_page_lruvec(page, pgdat);
+ spin_lock_irq(&lruvec->lru_lock);
+ rcu_read_unlock();
+
+ /* lruvec may changed in commit_charge() */
+ if (lruvec != mem_cgroup_page_lruvec(page, pgdat)) {
+ spin_unlock_irq(&lruvec->lru_lock);
+ goto again;
+ }
+
+ return lruvec;
+}
>
> You also need to use page_memcg_rcu() to insert the appropriate
> lockless access barriers, which mem_cgroup_page_lruvec() does not do
> since it's designed for use with pgdat->lru_lock.
>
Since the page_memcg_rcu can not know it under a spin_lock, guess the following enhance is fine:
@@ -1225,7 +1224,7 @@ struct lruvec *mem_cgroup_page_lruvec(struct page *page, struct pglist_data *pgd
goto out;
}
- memcg = page->mem_cgroup;
+ memcg = READ_ONCE(page->mem_cgroup);
/*
Millions thanks!
Alex
next prev parent reply other threads:[~2019-11-19 10:04 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-11-16 3:14 [PATCH v3 0/8] per lruvec lru_lock for memcg Alex Shi
2019-11-16 3:15 ` [PATCH v3 1/7] mm/lru: add per lruvec lock " Alex Shi
2019-11-16 6:28 ` Shakeel Butt
2019-11-18 2:44 ` Alex Shi
2019-11-18 12:08 ` Matthew Wilcox
2019-11-18 12:37 ` Alex Shi
2019-11-19 10:05 ` Alex Shi
2019-11-16 3:15 ` [PATCH v3 2/7] mm/lruvec: add irqsave flags into lruvec struct Alex Shi
2019-11-16 6:31 ` Shakeel Butt
2019-11-18 2:52 ` Alex Shi
2019-11-22 6:46 ` Christoph Hellwig
2019-11-16 3:15 ` [PATCH v3 3/7] mm/lru: replace pgdat lru_lock with lruvec lock Alex Shi
2019-11-16 4:38 ` Matthew Wilcox
2019-11-18 11:55 ` Alex Shi
2019-11-18 12:14 ` Matthew Wilcox
2019-11-18 12:31 ` Alex Shi
2019-11-18 12:34 ` Matthew Wilcox
2019-11-19 10:14 ` Alex Shi
2019-11-16 7:03 ` Shakeel Butt
2019-11-18 12:23 ` Alex Shi
2019-11-18 12:31 ` Matthew Wilcox
2019-11-19 10:08 ` Alex Shi
2019-11-18 16:11 ` Johannes Weiner
2019-11-19 10:04 ` Alex Shi [this message]
2019-11-19 2:10 ` Daniel Jordan
2019-11-19 10:10 ` Alex Shi
2019-11-16 3:15 ` [PATCH v3 4/7] mm/lru: only change the lru_lock iff page's lruvec is different Alex Shi
2019-11-16 3:15 ` [PATCH v3 5/7] mm/pgdat: remove pgdat lru_lock Alex Shi
2019-11-16 3:15 ` [PATCH v3 6/7] mm/lru: likely enhancement Alex Shi
2019-11-16 3:15 ` [PATCH v3 7/7] mm/lru: revise the comments of lru_lock Alex Shi
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