From: Chris Down <chris@chrisdown.name>
To: Yafang Shao <laoar.shao@gmail.com>
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 02:16:26 +0100 [thread overview]
Message-ID: <20200430011626.GA2754277@chrisdown.name> (raw)
In-Reply-To: <CALOAHbCotD1-+o_XZPU_4_i8Nn98r5F_5NpGVd=z6UG=rUcCmA@mail.gmail.com>
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").
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.
next prev parent reply other threads:[~2020-04-30 1:16 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 [this message]
2020-04-30 1:31 ` Yafang Shao
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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