Re: [patch] mm, slab: show total unreclaimable slab footprint on oom

[Harry Yoo <harry.yoo@oracle.com>]

On Sat, Apr 19, 2025 at 07:26:11PM -0700, David Rientjes wrote:
> When there is a large amount of unreclaimable slab memory in use at the
> time of oom kill, what really matters is the memory footprint that it
> consumes rather than only the number of active and total objects.
>
> Include the memory footprint in the kernel log for debugging.
>
> This may overestimate the amount of memory since slab pages may not be
> all of the same order, but it gives a useful upper bound for
> understanding where all the memory is going similar to slabinfo.
>
> At the same time, align the fields for some lengthy slab cache names such
> as fsnotify_mark_connector.
> 
> Signed-off-by: David Rientjes <rientjes@google.com>
> ---

Reviewed-by: Harry Yoo <harry.yoo@oracle.com>

By the way would it overkill to maintain a slab usage counter per
kmem_cache_node (Yes. one more atomic in allocate_slab()/discard_slab())
Or it doesn't need to be that accurate?

-- 
Cheers,
Harry / Hyeonggon

>  mm/slab_common.c | 9 +++++----
>  1 file changed, 5 insertions(+), 4 deletions(-)
> 
> diff --git a/mm/slab_common.c b/mm/slab_common.c
> --- a/mm/slab_common.c
> +++ b/mm/slab_common.c
> @@ -1145,7 +1145,7 @@ void dump_unreclaimable_slab(void)
>  	}
>  
>  	pr_info("Unreclaimable slab info:\n");
> -	pr_info("Name                      Used          Total\n");
> +	pr_info("Name                            Active_objs   Total_objs       Memory\n");
>  
>  	list_for_each_entry(s, &slab_caches, list) {
>  		if (s->flags & SLAB_RECLAIM_ACCOUNT)
> @@ -1154,9 +1154,10 @@ void dump_unreclaimable_slab(void)
>  		get_slabinfo(s, &sinfo);
>  
>  		if (sinfo.num_objs > 0)
> -			pr_info("%-17s %10luKB %10luKB\n", s->name,
> -				(sinfo.active_objs * s->size) / 1024,
> -				(sinfo.num_objs * s->size) / 1024);
> +			pr_info("%-30s %10luKB %10luKB %10luKB\n", s->name,
> +				(sinfo.active_objs * s->size) >> 10,
> +				(sinfo.num_objs * s->size) >> 10,
> +				sinfo.num_slabs << (sinfo.cache_order + PAGE_SHIFT - 10));
>  	}
>  	mutex_unlock(&slab_mutex);
>  }