From: Kirill Tkhai <ktkhai@virtuozzo.com>
To: David Rientjes <rientjes@google.com>
Cc: Michal Hocko <mhocko@kernel.org>,
Wei Yang <richardw.yang@linux.intel.com>,
hannes@cmpxchg.org, vdavydov.dev@gmail.com,
akpm@linux-foundation.org, kirill.shutemov@linux.intel.com,
yang.shi@linux.alibaba.com, cgroups@vger.kernel.org,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
alexander.duyck@gmail.com, stable@vger.kernel.org
Subject: Re: [Patch v3] mm: thp: grab the lock before manipulation defer list
Date: Fri, 17 Jan 2020 12:42:05 +0300 [thread overview]
Message-ID: <11ba0af7-c2b2-83f9-ac55-7793cedb8028@virtuozzo.com> (raw)
In-Reply-To: <alpine.DEB.2.21.2001170132090.20618@chino.kir.corp.google.com>
On 17.01.2020 12:32, David Rientjes wrote:
> On Fri, 17 Jan 2020, Kirill Tkhai wrote:
>
>>>> I think that's a good point, especially considering that the current code
>>>> appears to unconditionally place any compound page on the deferred split
>>>> queue of the destination memcg. The correct list that it should appear
>>>> on, I believe, depends on whether the pmd has been split for the process
>>>> being moved: note the MC_TARGET_PAGE caveat in
>>>> mem_cgroup_move_charge_pte_range() that does not move the charge for
>>>> compound pages with split pmds. So when mem_cgroup_move_account() is
>>>> called with compound == true, we're moving the charge of the entire
>>>> compound page: why would it appear on that memcg's deferred split queue?
>>>
>>> I believe Kirill asked how do we know that the page should be actually
>>> added to the deferred list just from the list_empty check. In other
>>> words what if the page hasn't been split at all?
>>
>> Yes, I'm talking about this. Function mem_cgroup_move_account() adds every
>> huge page to the deferred list, while we need to do that only for pages,
>> which are queued for splitting...
>>
>
> Yup, and that appears broken before Wei's patch. Since we only migrate
> charges of entire compound pages (we have a mapping pmd, the underlying
> page cannot be split), it should not appear on the deferred split queue
> for any memcg, right?
Hm. Can't a huge page be mapped in two tasks:
1)the first task unmapped a part of page and initiated splitting,
2)the second task still refers the whole page,
then we move account for the second task?
next prev parent reply other threads:[~2020-01-17 9:42 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-16 1:31 Wei Yang
2020-01-16 9:35 ` Kirill Tkhai
2020-01-16 22:01 ` David Rientjes
2020-01-17 0:47 ` Wei Yang
2020-01-17 9:10 ` Michal Hocko
2020-01-17 9:26 ` Kirill Tkhai
2020-01-17 9:32 ` David Rientjes
2020-01-17 9:42 ` Kirill Tkhai [this message]
2020-01-17 11:59 ` Michal Hocko
2020-01-17 9:31 ` David Rientjes
2020-01-17 15:38 ` Kirill A. Shutemov
2020-01-17 19:11 ` David Rientjes
2020-01-17 19:17 ` Yang Shi
2020-01-17 22:18 ` Wei Yang
2020-01-17 22:57 ` Kirill A. Shutemov
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