From: Johannes Weiner <hannes@cmpxchg.org>
To: Michal Hocko <mhocko@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Minchan Kim <minchan@kernel.org>,
"Kirill A. Shutemov" <kirill@shutemov.name>,
Vladimir Davydov <vdavydov@parallels.com>,
linux-mm@kvack.org, LKML <linux-kernel@vger.kernel.org>,
Michal Hocko <mhocko@suse.com>
Subject: Re: [PATCH mmotm] memcg: Ignore partial THP when moving task
Date: Tue, 8 Dec 2015 12:35:28 -0500 [thread overview]
Message-ID: <20151208173528.GA32265@cmpxchg.org> (raw)
In-Reply-To: <1449594789-15866-1-git-send-email-mhocko@kernel.org>
On Tue, Dec 08, 2015 at 06:13:09PM +0100, Michal Hocko wrote:
> From: Michal Hocko <mhocko@suse.com>
>
> After "mm: rework mapcount accounting to enable 4k mapping of THPs"
> it is possible to have a partial THP accessible via ptes. Memcg task
> migration code is not prepared for this situation and uncharges the tail
> page from the original memcg while the original THP is still charged via
> the head page which is not mapped to the moved task. The page counter
> of the origin memcg will underflow when the whole THP is uncharged later
> on and lead to:
> WARNING: CPU: 0 PID: 1340 at mm/page_counter.c:26 page_counter_cancel+0x34/0x40()
> reported by Minchan Kim.
>
> This patch prevents from the underflow by skipping any partial THP pages
> in mem_cgroup_move_charge_pte_range. PageTransCompound is checked when
> we do pte walk. This means that a process might leave a partial THP
> behind in the original memcg if there is no other process mapping it via
> pmd but this is considered acceptable because it shouldn't happen often
> and this is not considered a memory leak because the original THP is
> still accessible and reclaimable. Moreover the task migration has always
> been racy and never guaranteed to move all pages.
>
> Reported-by: Minchan Kim <minchan@kernel.org>
> Acked-by: Johannes Weiner <hannes@cmpxchg.org>
> Signed-off-by: Michal Hocko <mhocko@suse.com>
> ---
>
> Hi,
> this is a patch tested by Minchan in the original thread [1]. I have
> only replaced PageCompound with PageTransCompound because other similar
> fixes in mmotm used this one. The underlying implementation is the same.
> Johannes, I have kept your a-b but let me know if you are not OK with the
> changelog.
Looks good to me, thanks Michal. Please keep my Acked-by.
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next prev parent reply other threads:[~2015-12-08 17:35 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-12-08 17:13 Michal Hocko
2015-12-08 17:35 ` Johannes Weiner [this message]
2015-12-09 9:07 ` Michal Hocko
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