Re: [PATCH 2/2] mm: oom: dump single excessive slab cache when oom

[Yang Shi]

On 10/26/17 7:53 AM, Michal Hocko wrote:
> 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.

OK.

> > 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.

Since we just need the total memory size of the node for NUMA 
constrained OOM, we should be able to use show_mem_node_skip() to bring 
in nodemask.

> 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.

I don't get you. Do you mean the benefit is not that much with just 
dumping excessive slab caches?

Thanks,
Yang


>   
> > Dump single excessive slab cache if its size is > 10% of total system
>
> s@single@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@xxxxxxxxxx>
> > Signed-off-by: Yang Shi <yang.s@xxxxxxxxxxxxxxx>
> > ---
> >   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