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Date:   Thu, 26 Oct 2017 16:53:12 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Yang Shi <yang.s@...baba-inc.com>
Cc:     cl@...ux.com, penberg@...nel.org, rientjes@...gle.com,
        iamjoonsoo.kim@....com, akpm@...ux-foundation.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] mm: oom: dump single excessive slab cache when oom

On Thu 26-10-17 06:49:00, Yang Shi wrote:
> Per the discussion with David [1], it looks more reasonable to just dump

Please try to avoid external references in the changelog as much as
possible.

> the single excessive slab cache instead of dumping all slab caches when
> oom.

You meant to say
"to just dump all slab caches which excess 10% of the total memory."

While we are at it. Abusing calc_mem_size seems to be rather clumsy and
tt is not nodemask aware so you the whole thing is dubious for NUMA
constrained OOMs.

The more I think about this the more I am convinced that this is just
fiddling with the code without a good reason and without much better
outcome.
 
> Dump single excessive slab cache if its size is > 10% of total system

s@...gle@all@

> memory size when oom regardless it is unreclaimable.
> 
> [1] https://marc.info/?l=linux-mm&m=150819933626604&w=2
> 
> Suggested-by: David Rientjes <rientjes@...gle.com>
> Signed-off-by: Yang Shi <yang.s@...baba-inc.com>
> ---
>  mm/oom_kill.c    | 22 +---------------------
>  mm/slab.h        |  4 ++--
>  mm/slab_common.c | 21 ++++++++++++++++-----
>  3 files changed, 19 insertions(+), 28 deletions(-)
> 
> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> index 26add8a..f996f29 100644
> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -162,25 +162,6 @@ static bool oom_unkillable_task(struct task_struct *p,
>  	return false;
>  }
>  
> -/*
> - * Print out unreclaimble slabs info when unreclaimable slabs amount is greater
> - * than all user memory (LRU pages)
> - */
> -static bool is_dump_unreclaim_slabs(void)
> -{
> -	unsigned long nr_lru;
> -
> -	nr_lru = global_node_page_state(NR_ACTIVE_ANON) +
> -		 global_node_page_state(NR_INACTIVE_ANON) +
> -		 global_node_page_state(NR_ACTIVE_FILE) +
> -		 global_node_page_state(NR_INACTIVE_FILE) +
> -		 global_node_page_state(NR_ISOLATED_ANON) +
> -		 global_node_page_state(NR_ISOLATED_FILE) +
> -		 global_node_page_state(NR_UNEVICTABLE);
> -
> -	return (global_node_page_state(NR_SLAB_UNRECLAIMABLE) > nr_lru);
> -}
> -
>  /**
>   * oom_badness - heuristic function to determine which candidate task to kill
>   * @p: task struct of which task we should calculate
> @@ -443,8 +424,7 @@ static void dump_header(struct oom_control *oc, struct task_struct *p)
>  		mem_cgroup_print_oom_info(oc->memcg, p);
>  	else {
>  		show_mem(SHOW_MEM_FILTER_NODES, oc->nodemask);
> -		if (is_dump_unreclaim_slabs())
> -			dump_unreclaimable_slab();
> +		dump_slab_cache();
>  	}
>  	if (sysctl_oom_dump_tasks)
>  		dump_tasks(oc->memcg, oc->nodemask);
> diff --git a/mm/slab.h b/mm/slab.h
> index 6a86025..818b569 100644
> --- a/mm/slab.h
> +++ b/mm/slab.h
> @@ -507,9 +507,9 @@ static inline struct kmem_cache_node *get_node(struct kmem_cache *s, int node)
>  int memcg_slab_show(struct seq_file *m, void *p);
>  
>  #if defined(CONFIG_SLAB) || defined(CONFIG_SLUB_DEBUG)
> -void dump_unreclaimable_slab(void);
> +void dump_slab_cache(void);
>  #else
> -static inline void dump_unreclaimable_slab(void)
> +static inline void dump_slab_cache(void)
>  {
>  }
>  #endif
> diff --git a/mm/slab_common.c b/mm/slab_common.c
> index 1b14fe0..e5bfa07 100644
> --- a/mm/slab_common.c
> +++ b/mm/slab_common.c
> @@ -1311,7 +1311,18 @@ static int slab_show(struct seq_file *m, void *p)
>  	return 0;
>  }
>  
> -void dump_unreclaimable_slab(void)
> +static bool inline is_dump_slabs(struct kmem_cache *s, struct slabinfo *sinfo)
> +{
> +	unsigned long total = 0, reserved = 0, highmem = 0;
> +	unsigned long slab_size = sinfo->num_objs * s->size;
> +
> +	calc_mem_size(&total, &reserved, &highmem);
> +
> +	/* Check if single slab > 10% of total memory size */
> +	return (slab_size > (total * PAGE_SIZE / 10));
> +}
> +
> +void dump_slab_cache(void)
>  {
>  	struct kmem_cache *s, *s2;
>  	struct slabinfo sinfo;
> @@ -1324,20 +1335,20 @@ void dump_unreclaimable_slab(void)
>  	 * without acquiring the mutex.
>  	 */
>  	if (!mutex_trylock(&slab_mutex)) {
> -		pr_warn("excessive unreclaimable slab but cannot dump stats\n");
> +		pr_warn("excessive slab cache but cannot dump stats\n");
>  		return;
>  	}
>  
> -	pr_info("Unreclaimable slab info:\n");
> +	pr_info("The list of excessive single slab cache:\n");
>  	pr_info("Name                      Used          Total\n");
>  
>  	list_for_each_entry_safe(s, s2, &slab_caches, list) {
> -		if (!is_root_cache(s) || (s->flags & SLAB_RECLAIM_ACCOUNT))
> +		if (!is_root_cache(s))
>  			continue;
>  
>  		get_slabinfo(s, &sinfo);
>  
> -		if (sinfo.num_objs > 0)
> +		if (is_dump_slabs(s, &sinfo))
>  			pr_info("%-17s %10luKB %10luKB\n", cache_name(s),
>  				(sinfo.active_objs * s->size) / 1024,
>  				(sinfo.num_objs * s->size) / 1024);
> -- 
> 1.8.3.1

-- 
Michal Hocko
SUSE Labs

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