Re: [PATCH 2/2] mm: Consider subtrees in memory.events

Tejun Heo
2019-01-28T14:30:40Z

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