linux-kernel - Re: [PATCH] mm: memcontrol: Expose THP events on a per-memcg basis

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Date:   Tue, 29 Jan 2019 17:15:49 -0500
From:   Johannes Weiner <hannes@...xchg.org>
To:     Chris Down <chris@...isdown.name>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Tejun Heo <tj@...nel.org>, Roman Gushchin <guro@...com>,
        linux-kernel@...r.kernel.org, cgroups@...r.kernel.org,
        linux-mm@...ck.org, kernel-team@...com
Subject: Re: [PATCH] mm: memcontrol: Expose THP events on a per-memcg basis

On Tue, Jan 29, 2019 at 03:58:52PM -0500, Chris Down wrote:
> Currently THP allocation events data is fairly opaque, since you can
> only get it system-wide. This patch makes it easier to reason about
> transparent hugepage behaviour on a per-memcg basis.
> 
> For anonymous THP-backed pages, we already have MEMCG_RSS_HUGE in v1,
> which is used for v1's rss_huge [sic]. This is reused here as it's
> fairly involved to untangle NR_ANON_THPS right now to make it
> per-memcg, since right now some of this is delegated to rmap before we
> have any memcg actually assigned to the page. It's a good idea to rework
> that, but let's leave untangling THP allocation for a future patch.
>
> Signed-off-by: Chris Down <chris@...isdown.name>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Johannes Weiner <hannes@...xchg.org>
> Cc: Tejun Heo <tj@...nel.org>
> Cc: Roman Gushchin <guro@...com>
> Cc: linux-kernel@...r.kernel.org
> Cc: cgroups@...r.kernel.org
> Cc: linux-mm@...ck.org
> Cc: kernel-team@...com

Looks good to me. It's useful to know if a cgroup is getting the THP
coverage and allocation policy it's asking for.

Acked-by: Johannes Weiner <hannes@...xchg.org>

The fallback numbers could be useful as well, but they're tricky to
obtain as there isn't an obvious memcg context. We can do them later.