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SubjectRe: [PATCH] mm, slab: eagerly delete inactive offlined SLABs
[Cc Vladimir]

On Wed 21-03-18 15:43:01, Shakeel Butt wrote:
> With kmem cgroup support, high memcgs churn can leave behind a lot of
> empty kmem_caches. Usually such kmem_caches will be destroyed when the
> corresponding memcg gets released but the memcg release can be
> arbitrarily delayed. These empty kmem_caches wastes cache_reaper's time.
> So, the reaper should destroy such empty offlined kmem_caches.
>
> Signed-off-by: Shakeel Butt <shakeelb@google.com>
> ---
> mm/slab.c | 18 ++++++++++++++++--
> mm/slab.h | 15 +++++++++++++++
> mm/slab_common.c | 2 +-
> 3 files changed, 32 insertions(+), 3 deletions(-)
>
> diff --git a/mm/slab.c b/mm/slab.c
> index 66f2db98f026..9c174a799ffb 100644
> --- a/mm/slab.c
> +++ b/mm/slab.c
> @@ -4004,6 +4004,16 @@ static void drain_array(struct kmem_cache *cachep, struct kmem_cache_node *n,
> slabs_destroy(cachep, &list);
> }
>
> +static bool is_slab_active(struct kmem_cache *cachep)
> +{
> + int node;
> + struct kmem_cache_node *n;
> +
> + for_each_kmem_cache_node(cachep, node, n)
> + if (READ_ONCE(n->total_slabs) - n->free_slabs)
> + return true;
> + return false;
> +}
> /**
> * cache_reap - Reclaim memory from caches.
> * @w: work descriptor
> @@ -4018,7 +4028,7 @@ static void drain_array(struct kmem_cache *cachep, struct kmem_cache_node *n,
> */
> static void cache_reap(struct work_struct *w)
> {
> - struct kmem_cache *searchp;
> + struct kmem_cache *searchp, *tmp;
> struct kmem_cache_node *n;
> int node = numa_mem_id();
> struct delayed_work *work = to_delayed_work(w);
> @@ -4027,7 +4037,7 @@ static void cache_reap(struct work_struct *w)
> /* Give up. Setup the next iteration. */
> goto out;
>
> - list_for_each_entry(searchp, &slab_caches, list) {
> + list_for_each_entry_safe(searchp, tmp, &slab_caches, list) {
> check_irq_on();
>
> /*
> @@ -4061,6 +4071,10 @@ static void cache_reap(struct work_struct *w)
> 5 * searchp->num - 1) / (5 * searchp->num));
> STATS_ADD_REAPED(searchp, freed);
> }
> +
> + /* Eagerly delete inactive kmem_cache of an offlined memcg. */
> + if (!is_memcg_online(searchp) && !is_slab_active(searchp))
> + shutdown_cache(searchp);
> next:
> cond_resched();
> }
> diff --git a/mm/slab.h b/mm/slab.h
> index e8981e811c45..e911b10efae7 100644
> --- a/mm/slab.h
> +++ b/mm/slab.h
> @@ -166,6 +166,7 @@ static inline slab_flags_t kmem_cache_flags(unsigned int object_size,
> SLAB_TEMPORARY | \
> SLAB_ACCOUNT)
>
> +int shutdown_cache(struct kmem_cache *s);
> int __kmem_cache_shutdown(struct kmem_cache *);
> void __kmem_cache_release(struct kmem_cache *);
> int __kmem_cache_shrink(struct kmem_cache *);
> @@ -290,6 +291,15 @@ static __always_inline void memcg_uncharge_slab(struct page *page, int order,
> memcg_kmem_uncharge(page, order);
> }
>
> +static __always_inline bool is_memcg_online(struct kmem_cache *s)
> +{
> + if (!memcg_kmem_enabled())
> + return true;
> + if (is_root_cache(s))
> + return true;
> + return mem_cgroup_online(s->memcg_params.memcg);
> +}
> +
> extern void slab_init_memcg_params(struct kmem_cache *);
> extern void memcg_link_cache(struct kmem_cache *s);
> extern void slab_deactivate_memcg_cache_rcu_sched(struct kmem_cache *s,
> @@ -342,6 +352,11 @@ static inline void memcg_uncharge_slab(struct page *page, int order,
> {
> }
>
> +static inline bool is_memcg_online(struct kmem_cache *s)
> +{
> + return true;
> +}
> +
> static inline void slab_init_memcg_params(struct kmem_cache *s)
> {
> }
> diff --git a/mm/slab_common.c b/mm/slab_common.c
> index 61ab2ca8bea7..d197e878636b 100644
> --- a/mm/slab_common.c
> +++ b/mm/slab_common.c
> @@ -573,7 +573,7 @@ static void slab_caches_to_rcu_destroy_workfn(struct work_struct *work)
> }
> }
>
> -static int shutdown_cache(struct kmem_cache *s)
> +int shutdown_cache(struct kmem_cache *s)
> {
> /* free asan quarantined objects */
> kasan_cache_shutdown(s);
> --
> 2.17.0.rc0.231.g781580f067-goog

--
Michal Hocko
SUSE Labs

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