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

[Michal Hocko <mhocko@suse.com>]

On Fri 07-11-25 15:40:41, Shakeel Butt 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.

Makes sense to me.

> Signed-off-by: Shakeel Butt <shakeel.butt@linux.dev>

Acked-by: Michal Hocko <mhocko@suse.com>
Thanks!

> ---
>  include/linux/memcontrol.h |  5 +++++
>  mm/memcontrol.c            | 13 +++++++++++++
>  mm/oom_kill.c              |  1 +
>  mm/page_alloc.c            |  1 +
>  4 files changed, 20 insertions(+)
> 
> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index 8d2e250535a8..6861f0ff02b5 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -1779,6 +1779,7 @@ static inline bool memcg_is_dying(struct mem_cgroup *memcg)
>  	return memcg ? css_is_dying(&memcg->css) : false;
>  }
>  
> +void mem_cgroup_show_protected_memory(struct mem_cgroup *memcg);
>  #else
>  static inline bool mem_cgroup_kmem_disabled(void)
>  {
> @@ -1850,6 +1851,10 @@ static inline bool memcg_is_dying(struct mem_cgroup *memcg)
>  {
>  	return false;
>  }
> +
> +static inline void mem_cgroup_show_protected_memory(struct mem_cgroup *memcg)
> +{
> +}
>  #endif /* CONFIG_MEMCG */
>  
>  #if defined(CONFIG_MEMCG) && defined(CONFIG_ZSWAP)
> 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));
> +}
> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> index c145b0feecc1..5eb11fbba704 100644
> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -472,6 +472,7 @@ static void dump_header(struct oom_control *oc)
>  		if (should_dump_unreclaim_slab())
>  			dump_unreclaimable_slab();
>  	}
> +	mem_cgroup_show_protected_memory(oc->memcg);
>  	if (sysctl_oom_dump_tasks)
>  		dump_tasks(oc);
>  }
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index e4efda1158b2..26be5734253f 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -3977,6 +3977,7 @@ static void warn_alloc_show_mem(gfp_t gfp_mask, nodemask_t *nodemask)
>  		filter &= ~SHOW_MEM_FILTER_NODES;
>  
>  	__show_mem(filter, nodemask, gfp_zone(gfp_mask));
> +	mem_cgroup_show_protected_memory(NULL);
>  }
>  
>  void warn_alloc(gfp_t gfp_mask, nodemask_t *nodemask, const char *fmt, ...)
> -- 
> 2.47.3

-- 
Michal Hocko
SUSE Labs