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From: Tejun Heo <tj@kernel.org>
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>,
	Dennis Zhou <dennis@kernel.org>,
	linux-kernel@vger.kernel.org, cgroups@vger.kernel.org,
	linux-mm@kvack.org, kernel-team@fb.com
Subject: Re: [PATCH 2/2] mm: Consider subtrees in memory.events
Date: Mon, 28 Jan 2019 06:30:33 -0800	[thread overview]
Message-ID: <20190128143033.GN50184@devbig004.ftw2.facebook.com> (raw)
In-Reply-To: <20190123223144.GA10798@chrisdown.name>

On Wed, Jan 23, 2019 at 05:31:44PM -0500, Chris Down wrote:
> memory.stat and other files already consider subtrees in their output,
> and we should too in order to not present an inconsistent interface.
> 
> The current situation is fairly confusing, because people interacting
> with cgroups expect hierarchical behaviour in the vein of memory.stat,
> cgroup.events, and other files. For example, this causes confusion when
> debugging reclaim events under low, as currently these always read "0"
> at non-leaf memcg nodes, which frequently causes people to misdiagnose
> breach behaviour. The same confusion applies to other counters in this
> file when debugging issues.
> 
> Aggregation is done at write time instead of at read-time since these
> counters aren't hot (unlike memory.stat which is per-page, so it does it
> at read time), and it makes sense to bundle this with the file
> notifications.
...
> Signed-off-by: Chris Down <chris@chrisdown.name>
> Acked-by: Johannes Weiner <hannes@cmpxchg.org>

Acked-by: Tejun Heo <tj@kernel.org>

Michal has a valid counterpoint that this is a change in userland
visible behavior but to me this patch seems to be more of a bug fix
than anything else in that it's addressing an obvious inconsistency in
the interface.

Thanks.

-- 
tejun

  parent reply	other threads:[~2019-01-28 14:30 UTC|newest]

Thread overview: 53+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-01-23 22:31 [PATCH 2/2] mm: Consider subtrees in memory.events Chris Down
2019-01-24  0:24 ` Roman Gushchin
2019-01-24  1:03   ` Chris Down
2019-01-24  8:22 ` Michal Hocko
2019-01-24 15:21   ` Tejun Heo
2019-01-24 15:51     ` Michal Hocko
2019-01-24 16:00   ` Johannes Weiner
2019-01-24 17:01     ` Michal Hocko
2019-01-24 18:23       ` Johannes Weiner
2019-01-25  8:42         ` Michal Hocko
2019-01-25 16:51           ` Tejun Heo
2019-01-25 17:37             ` Michal Hocko
2019-01-25 17:37               ` Michal Hocko
2019-01-25 18:28               ` Tejun Heo
2019-01-28 12:51                 ` Michal Hocko
2019-01-28 14:28                   ` Tejun Heo
2019-01-28 14:52                     ` Michal Hocko
2019-01-28 14:54                       ` Tejun Heo
2019-01-28 15:18                         ` Michal Hocko
2019-01-28 15:41                           ` Tejun Heo
2019-01-28 17:05                             ` Michal Hocko
2019-01-28 17:49                               ` Tejun Heo
2019-01-29 14:43                                 ` Michal Hocko
2019-01-29 14:52                                   ` Tejun Heo
2019-01-30 16:50                                     ` Michal Hocko
2019-01-30 17:06                                       ` Tejun Heo
2019-01-30 17:41                                         ` Michal Hocko
2019-01-30 17:52                                           ` Tejun Heo
2019-01-30 18:16                                             ` Michal Hocko
2019-01-30 19:11                                         ` Shakeel Butt
2019-01-30 19:11                                           ` Shakeel Butt
2019-01-30 19:27                                           ` Johannes Weiner
2019-01-30 19:30                                             ` Johannes Weiner
2019-01-30 19:37                                               ` Shakeel Butt
2019-01-30 19:37                                                 ` Shakeel Butt
2019-01-30 19:23                   ` Johannes Weiner
2019-01-30 20:05                     ` Michal Hocko
2019-01-30 21:31                       ` Johannes Weiner
2019-01-31  8:58                         ` Michal Hocko
2019-01-31 16:22                           ` Johannes Weiner
2019-02-01 10:27                             ` Michal Hocko
2019-02-01 16:34                               ` Johannes Weiner
2019-01-28 15:59                 ` Shakeel Butt
2019-01-28 15:59                   ` Shakeel Butt
2019-01-28 16:05                   ` Tejun Heo
2019-01-28 16:08                     ` Shakeel Butt
2019-01-28 16:08                       ` Shakeel Butt
2019-01-28 16:12                       ` Tejun Heo
2019-01-28 14:30 ` Tejun Heo [this message]
2019-02-08 22:43 ` [PATCH v2 1/2] mm: Rename ambiguously named memory.stat counters and functions Chris Down
2019-02-08 22:44   ` [PATCH v2 2/2] mm: Consider subtrees in memory.events Chris Down
2019-02-11 19:01     ` Johannes Weiner
2019-02-11 18:55   ` [PATCH v2 1/2] mm: Rename ambiguously named memory.stat counters and functions Johannes Weiner

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