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SubjectRe: [PATCH 2/2] mm: oom: show unreclaimable slab info when kernel panic
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(...);

> 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)

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