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

[Yang Shi]

On 9/20/17 2:00 PM, David Rientjes wrote:
> On Thu, 21 Sep 2017, Yang Shi wrote:
>
> > diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> > index 99736e0..173c423 100644
> > --- a/mm/oom_kill.c
> > +++ b/mm/oom_kill.c
> > @@ -43,6 +43,7 @@
> >   
> >   #include <asm/tlb.h>
> >   #include "internal.h"
> > +#include "slab.h"
> >   
> >   #define CREATE_TRACE_POINTS
> >   #include <trace/events/oom.h>
> > @@ -427,6 +428,14 @@ static void dump_header(struct oom_control *oc, struct task_struct *p)
> >   		dump_tasks(oc->memcg, oc->nodemask);
> >   }
> >   
> > +static void dump_header_with_slabinfo(struct oom_control *oc, struct task_struct *p)
> > +{
> > +	dump_header(oc, p);
> > +
> > +	if (IS_ENABLED(CONFIG_SLABINFO))
> > +		show_unreclaimable_slab();
> > +}
> > +
> >   /*
> >    * Number of OOM victims in flight
> >    */
>
> I don't think we need a new function for this.  Where you want to dump
> unreclaimable slab before panic, just call a new dump_unreclaimable_slab()
> function that gets declared in slab.h that is a no-op when CONFIG_SLABINFO
> is disabled.  We just want to do
>
> 	dump_header(...);
> 	dump_unreclaimable_slab(...);
> 	panic(...);

Thanks for the comment, they will be solved in v4.

Yang

> > diff --git a/mm/slab.c b/mm/slab.c
> > index 04dec48..4f4971c 100644
> > --- a/mm/slab.c
> > +++ b/mm/slab.c
> > @@ -4132,6 +4132,7 @@ void get_slabinfo(struct kmem_cache *cachep, struct slabinfo *sinfo)
> >   	sinfo->shared = cachep->shared;
> >   	sinfo->objects_per_slab = cachep->num;
> >   	sinfo->cache_order = cachep->gfporder;
> > +	sinfo->reclaim = is_reclaimable(cachep);
>
> We don't need a new field, we already have cachep->flags accessible.
>
> >   }
> >   
> >   void slabinfo_show_stats(struct seq_file *m, struct kmem_cache *cachep)
> > diff --git a/mm/slab.h b/mm/slab.h
> > index 0733628..2f1ebce 100644
> > --- a/mm/slab.h
> > +++ b/mm/slab.h
> > @@ -186,6 +186,7 @@ struct slabinfo {
> >   	unsigned int shared;
> >   	unsigned int objects_per_slab;
> >   	unsigned int cache_order;
> > +	unsigned int reclaim;
>
> Not needed.
>
> >   };
> >   
> >   void get_slabinfo(struct kmem_cache *s, struct slabinfo *sinfo);
> > @@ -352,6 +353,11 @@ static inline void memcg_link_cache(struct kmem_cache *s)
> >   
> >   #endif /* CONFIG_MEMCG && !CONFIG_SLOB */
> >   
> > +static inline bool is_reclaimable(struct kmem_cache *s)
> > +{
> > +	return (s->flags & SLAB_RECLAIM_ACCOUNT) ? true : false;
> > +}
> > +
>
> I don't think we need this.
>
> >   static inline struct kmem_cache *cache_from_obj(struct kmem_cache *s, void *x)
> >   {
> >   	struct kmem_cache *cachep;
> > @@ -504,6 +510,7 @@ static inline struct kmem_cache_node *get_node(struct kmem_cache *s, int node)
> >   void *memcg_slab_next(struct seq_file *m, void *p, loff_t *pos);
> >   void memcg_slab_stop(struct seq_file *m, void *p);
> >   int memcg_slab_show(struct seq_file *m, void *p);
> > +void show_unreclaimable_slab(void);
> >   
> >   void ___cache_free(struct kmem_cache *cache, void *x, unsigned long addr);
> >   
> > diff --git a/mm/slab_common.c b/mm/slab_common.c
> > index 904a83b..f2c6200 100644
> > --- 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)
> > +
>
> I don't think we need this.
>
> >   /*
> >    * Set of flags that will prevent slab merging
> >    */
> > @@ -1272,6 +1274,35 @@ static int slab_show(struct seq_file *m, void *p)
> >   	return 0;
> >   }
> >   
> > +void show_unreclaimable_slab()
>
> void show_unreclaimable_slab(void)
>
> > +{
> > +	struct kmem_cache *s = NULL;
>
> No initialization needed.
>
> > +	struct slabinfo sinfo;
> > +
> > +	memset(&sinfo, 0, sizeof(sinfo));
> > +
> > +	printk("Unreclaimable slab info:\n");
> > +	printk("Name                      Used          Total\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;
> > +
>
> We need to do the memset() here.
>
> > +		get_slabinfo(s, &sinfo);
> > +
> > +		if (!is_reclaimable(s) && sinfo.num_objs > 0)
> > +			printk("%-17s %10luKB %10luKB\n", cache_name(s), K(sinfo.active_objs * s->size), K(sinfo.num_objs * s->size));
>
> I think you can just check for SLAB_RECLAIM_ACCOUNT here.
>
> Everything in this function should be pr_info().
>
> > +	}
> > +}
> > +EXPORT_SYMBOL(show_unreclaimable_slab);
> > +#undef K
> > +
> >   #if defined(CONFIG_MEMCG) && !defined(CONFIG_SLOB)
> >   void *memcg_slab_start(struct seq_file *m, loff_t *pos)
> >   {
> > diff --git a/mm/slub.c b/mm/slub.c
> > index 163352c..5c17c0a 100644
> > --- a/mm/slub.c
> > +++ b/mm/slub.c
> > @@ -5872,6 +5872,7 @@ void get_slabinfo(struct kmem_cache *s, struct slabinfo *sinfo)
> >   	sinfo->num_slabs = nr_slabs;
> >   	sinfo->objects_per_slab = oo_objects(s->oo);
> >   	sinfo->cache_order = oo_order(s->oo);
> > +	sinfo->reclaim = is_reclaimable(s);
>
> Not needed.
>
> >   }
> >   
> >   void slabinfo_show_stats(struct seq_file *m, struct kmem_cache *s)