From: Wei Yang <richardw.yang@linux.intel.com>
To: David Rientjes <rientjes@google.com>
Cc: "Kirill A. Shutemov" <kirill@shutemov.name>,
Michal Hocko <mhocko@kernel.org>,
Wei Yang <richardw.yang@linux.intel.com>,
hannes@cmpxchg.org, vdavydov.dev@gmail.com,
akpm@linux-foundation.org, cgroups@vger.kernel.org,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
kirill.shutemov@linux.intel.com, yang.shi@linux.alibaba.com,
alexander.duyck@gmail.com
Subject: Re: [Patch v2] mm: thp: grab the lock before manipulation defer list
Date: Wed, 15 Jan 2020 09:19:27 +0800 [thread overview]
Message-ID: <20200115011927.GB4916@richard> (raw)
In-Reply-To: <alpine.DEB.2.21.2001141254460.84781@chino.kir.corp.google.com>
On Tue, Jan 14, 2020 at 12:57:22PM -0800, David Rientjes wrote:
>On Tue, 14 Jan 2020, Kirill A. Shutemov wrote:
>
>> split_huge_page_to_list() has page lock taken.
>>
>> free_transhuge_page() is in the free path and doesn't susceptible to the
>> race.
>>
>> deferred_split_scan() is trickier. list_move() should be safe against
>> list_empty() as it will not produce false-positive list_empty().
>> list_del_init() *should* (correct me if I'm wrong) be safe because the page
>> is freeing and memcg will not touch the page anymore.
>>
>> deferred_split_huge_page() is a problematic one. It called from
>> page_remove_rmap() path witch does require page lock. I don't see any
>> obvious way to exclude race with mem_cgroup_move_account() here.
>> Anybody else?
>>
>> Wei, could you rewrite the commit message with deferred_split_huge_page()
>> as a race source instead of split_huge_page_to_list()?
>>
>
>I think describing the race in terms of deferred_split_huge_page() makes
>the most sense and I'd prefer a cc to stable for 5.4+. Even getting the
>split_queue_len, which is unsigned long, to underflow because of a
>list_empty(page_deferred_list()) check that is no longer accurate after
>the lock is taken would be a significant issue for shrinkers.
Oh, you are right. Even the list is not corrupted between
deferred_split_scan() and mem_cgroup_move_account(), split_queue_len would be
in a wrong state.
Hmm... to some extend, the page lock complicates the picture a little here,
even it helps in some cases.
--
Wei Yang
Help you, Help me
next prev parent reply other threads:[~2020-01-15 1:19 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-09 14:30 Wei Yang
2020-01-09 18:52 ` David Rientjes
2020-01-09 18:58 ` Michal Hocko
2020-01-11 0:03 ` Kirill A. Shutemov
2020-01-12 2:28 ` Wei Yang
2020-01-12 22:57 ` Kirill A. Shutemov
2020-01-13 0:44 ` Wei Yang
2020-01-13 7:36 ` Kirill A. Shutemov
2020-01-13 8:23 ` Wei Yang
2020-01-14 9:31 ` Michal Hocko
2020-01-14 10:31 ` Kirill A. Shutemov
2020-01-14 10:59 ` Kirill A. Shutemov
2020-01-14 20:57 ` David Rientjes
2020-01-15 1:19 ` Wei Yang [this message]
2020-01-15 1:07 ` Wei Yang
2020-01-15 3:26 ` David Rientjes
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