From: Yafang Shao <laoar.shao@gmail.com>
To: Chris Down <chris@chrisdown.name>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Johannes Weiner <hannes@cmpxchg.org>,
Michal Hocko <mhocko@kernel.org>, Roman Gushchin <guro@fb.com>,
Linux MM <linux-mm@kvack.org>, Cgroups <cgroups@vger.kernel.org>,
LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 1/2] mm, memcg: Avoid stale protection values when cgroup is above protection
Date: Thu, 30 Apr 2020 09:31:23 +0800 [thread overview]
Message-ID: <CALOAHbCL_JJgcy9r99Kn81-o_t-fs_nQ+n7aKMHO-02QMCufEw@mail.gmail.com> (raw)
In-Reply-To: <20200430011626.GA2754277@chrisdown.name>
On Thu, Apr 30, 2020 at 9:16 AM Chris Down <chris@chrisdown.name> wrote:
>
> Hi Yafang,
>
> Yafang Shao writes:
> >Would you pls. add some comments above these newly added WRITE_ONCE() ?
> >E.g.
> >What does them mean to fix ?
> >Why do we must add WRITE_ONCE() and READ_ONCE here and there all over
> >the memcg protection ?
> >Otherwise, it may be harder to understand by the others.
>
> There is already discussion in the changelogs for previous store tear
> improvements. For example, b3a7822e5e75 ("mm, memcg: prevent
> mem_cgroup_protected store tearing").
>
I'm sorry that I missed the changelog in the other one.
So you'd better add these commit log or comment to this one again.
> WRITE_ONCE and READ_ONCE are standard compiler barriers, in this case, to avoid
> store tears from writes in another thread (effective protection caching is
> designed by its very nature to permit racing, but tearing is non-ideal).
>
> You can find out more about them in the "COMPILER BARRIER" section in
> Documentation/memory-barriers.txt. I'm not really seeing the value of adding an
> extra comment about this specific use of them, unless you have some more
> explicit concern.
My concern is why we add these barriers to memcg protection
specifically but don't add these barriers to the other memebers like
memcg->oom_group which has the same issue ?
What is the difference between these members and that members ?
--
Thanks
Yafang
next prev parent reply other threads:[~2020-04-30 1:32 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-28 18:26 [PATCH 0/2] mm: memcontrol: memory.{low,min} reclaim fix & cleanup Chris Down
2020-04-28 18:26 ` [PATCH 1/2] mm, memcg: Avoid stale protection values when cgroup is above protection Chris Down
2020-04-28 21:16 ` Johannes Weiner
2020-04-29 10:15 ` Michal Hocko
2020-04-29 10:53 ` Yafang Shao
2020-04-29 14:19 ` Johannes Weiner
2020-04-29 14:03 ` Johannes Weiner
2020-04-29 14:17 ` Yafang Shao
2020-04-29 14:27 ` Johannes Weiner
2020-04-29 14:31 ` Yafang Shao
2020-04-29 15:04 ` Michal Hocko
2020-04-29 16:56 ` Johannes Weiner
2020-04-30 14:57 ` Michal Hocko
2020-04-30 17:17 ` Roman Gushchin
2020-04-30 23:59 ` Yafang Shao
2020-05-04 7:23 ` Michal Hocko
2020-05-04 22:59 ` Roman Gushchin
2020-04-30 1:04 ` Yafang Shao
2020-04-30 1:16 ` Chris Down
2020-04-30 1:31 ` Yafang Shao [this message]
2020-04-30 1:46 ` Chris Down
2020-04-30 1:49 ` Yafang Shao
2020-04-28 18:27 ` [PATCH 2/2] mm, memcg: Decouple e{low,min} state mutations from protection checks Chris Down
2020-04-28 21:19 ` Johannes Weiner
2020-04-29 10:06 ` Michal Hocko
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