From: Michal Hocko <mhocko@kernel.org>
To: Kirill Tkhai <ktkhai@virtuozzo.com>,
g@suse.cz, kirill.shutemov@linux.intel.com
Cc: David Rientjes <rientjes@google.com>,
Wei Yang <richardw.yang@linux.intel.com>,
hannes@cmpxchg.org, vdavydov.dev@gmail.com,
akpm@linux-foundation.or, 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 12:59:35 +0100 [thread overview]
Message-ID: <20200117115935.GW19428@dhcp22.suse.cz> (raw)
In-Reply-To: <11ba0af7-c2b2-83f9-ac55-7793cedb8028@virtuozzo.com>
On Fri 17-01-20 12:42:05, Kirill Tkhai wrote:
> 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:
It can but it will get charged to only of the initially. I haven't
checked the THP code in that aspect but from what I remember subpages
shouldn't refer to different memcgs. Kirill Shutemov?
--
Michal Hocko
SUSE Labs
next prev parent reply other threads:[~2020-01-17 11:59 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
2020-01-17 11:59 ` Michal Hocko [this message]
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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