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SubjectRe: [PATCH 3/3] mm: oom: show unreclaimable slab info when unreclaimable slabs > user memory
On Wed 04-10-17 02:06:17, Yang Shi wrote:
> +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);
> +}

I am sorry I haven't pointed this earlier (I was following only half
way) but this should really be memcg aware. You are checking only global
counters. I do not think it is an absolute must to provide per-memcg
data but you should at least check !is_memcg_oom(oc).

[...]
> +void dump_unreclaimable_slab(void)
> +{
> + struct kmem_cache *s, *s2;
> + struct slabinfo sinfo;
> +
> + pr_info("Unreclaimable slab info:\n");
> + pr_info("Name Used Total\n");
> +
> + /*
> + * Here acquiring slab_mutex is risky since we don't prefer to get
> + * sleep in oom path. But, without mutex hold, it may introduce a
> + * risk of crash.
> + * Use mutex_trylock to protect the list traverse, dump nothing
> + * without acquiring the mutex.
> + */
> + if (!mutex_trylock(&slab_mutex))
> + return;

I would move the trylock up so that we do not get empty and confusing
Unreclaimable slab info: and add a note that we are not dumping anything
due to lock contention
pr_warn("excessive unreclaimable slab memory but cannot dump stats to give you more details\n");

Other than that this looks sensible to me.

> + list_for_each_entry_safe(s, s2, &slab_caches, list) {
> + if (!is_root_cache(s) || (s->flags & SLAB_RECLAIM_ACCOUNT))
> + continue;
> +
> + memset(&sinfo, 0, sizeof(sinfo));
> + get_slabinfo(s, &sinfo);
> +
> + if (sinfo.num_objs > 0)
> + pr_info("%-17s %10luKB %10luKB\n", cache_name(s),
> + (sinfo.active_objs * s->size) / 1024,
> + (sinfo.num_objs * s->size) / 1024);
> + }
> + mutex_unlock(&slab_mutex);
> +}
> +
> #if defined(CONFIG_MEMCG) && !defined(CONFIG_SLOB)
> void *memcg_slab_start(struct seq_file *m, loff_t *pos)
> {
> --
> 1.8.3.1

--
Michal Hocko
SUSE Labs

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