linux-kernel - Re: [PATCH] mm: memcg: dump memcg protection info on oom or alloc failures

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Message-ID: <20251108022639.73734-1-sj@kernel.org>
Date: Fri,  7 Nov 2025 18:26:38 -0800
From: SeongJae Park <sj@...nel.org>
To: Shakeel Butt <shakeel.butt@...ux.dev>
Cc: SeongJae Park <sj@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Johannes Weiner <hannes@...xchg.org>,
	Michal Hocko <mhocko@...nel.org>,
	Roman Gushchin <roman.gushchin@...ux.dev>,
	Muchun Song <muchun.song@...ux.dev>,
	David Rientjes <rientjes@...gle.com>,
	Vlastimil Babka <vbabka@...e.cz>,
	linux-mm@...ck.org,
	cgroups@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Meta kernel team <kernel-team@...a.com>
Subject: Re: [PATCH] mm: memcg: dump memcg protection info on oom or alloc failures

On Fri,  7 Nov 2025 15:40:41 -0800 Shakeel Butt <shakeel.butt@...ux.dev> wrote:

> Currently kernel dumps memory state on oom and allocation failures. One
> of the question usually raised on those dumps is why the kernel has not
> reclaimed the reclaimable memory instead of triggering oom. One
> potential reason is the usage of memory protection provided by memcg.
> So, let's also dump the memory protected by the memcg in such reports to
> ease the debugging.
> 
> Signed-off-by: Shakeel Butt <shakeel.butt@...ux.dev>
> ---
[...]
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index c34029e92bab..623446821b00 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -5636,3 +5636,16 @@ bool mem_cgroup_node_allowed(struct mem_cgroup *memcg, int nid)
>  {
>  	return memcg ? cpuset_node_allowed(memcg->css.cgroup, nid) : true;
>  }
> +
> +void mem_cgroup_show_protected_memory(struct mem_cgroup *memcg)
> +{
> +	if (mem_cgroup_disabled() || !cgroup_subsys_on_dfl(memory_cgrp_subsys))
> +		return;
> +
> +	if (!memcg)
> +		memcg = root_mem_cgroup;
> +
> +	pr_warn("Memory cgroup min protection %lukB -- low protection %lukB",
> +		K(atomic_long_read(&memcg->memory.children_min_usage)*PAGE_SIZE),
> +		K(atomic_long_read(&memcg->memory.children_low_usage)*PAGE_SIZE));
> +}

I didn't expect this function is showing the information by calling pr_warn().
To me, "show" feels like something for file operations, like memory_min_show().

What about s/show/dump/ on the name?  It makes it more consistent with the
subject of this patch, and other similar functions like dump_page() ?

No strong opinion.  The current name is also ok for me, but I'm just curious your thought.


Thanks,
SJ

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