linux-kernel - Re: [PATCH 2/2] mm: oom: show unreclaimable slab info when kernel panic

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Date:   Tue, 19 Sep 2017 13:57:15 -0700 (PDT)
From:   David Rientjes <rientjes@...gle.com>
To:     Yang Shi <yang.s@...baba-inc.com>
cc:     cl@...ux.com, penberg@...nel.org, iamjoonsoo.kim@....com,
        akpm@...ux-foundation.org, mhocko@...nel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] mm: oom: show unreclaimable slab info when kernel
 panic

On Tue, 19 Sep 2017, Yang Shi wrote:

> --- a/mm/slab_common.c
> +++ b/mm/slab_common.c
> @@ -35,6 +35,8 @@
>  static DECLARE_WORK(slab_caches_to_rcu_destroy_work,
>  		    slab_caches_to_rcu_destroy_workfn);
>  
> +#define K(x) ((x)/1024)
> +
>  /*
>   * Set of flags that will prevent slab merging
>   */
> @@ -1272,6 +1274,34 @@ static int slab_show(struct seq_file *m, void *p)
>  	return 0;
>  }
>  
> +void show_unreclaimable_slab()
> +{
> +	struct kmem_cache *s = NULL;
> +	struct slabinfo sinfo;
> +
> +	memset(&sinfo, 0, sizeof(sinfo));
> +
> +	printk("Unreclaimable slabs:\n");
> +
> +	/*
> +	 * Here acquiring slab_mutex is unnecessary since we don't prefer to
> +	 * get sleep in oom path right before kernel panic, and avoid race condition.
> +	 * Since it is already oom, so there should be not any big allocation
> +	 * which could change the statistics significantly.
> +	 */
> +	list_for_each_entry(s, &slab_caches, list) {
> +		if (!is_root_cache(s))
> +			continue;
> +
> +		get_slabinfo(s, &sinfo);
> +
> +		if (!is_reclaimable(s) && sinfo.num_objs > 0)
> +			printk("%-17s %luKB\n", cache_name(s), K(sinfo.num_objs * s->size));
> +	}

I like this, but could we be even more helpful by giving the user more 
information from sinfo beyond just the total size of objects allocated?