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SubjectRe: [PATCH v6 14/17] mm: Iterate only over charged shrinkers during memcg shrink_slab()
On Fri, May 18, 2018 at 11:44:01AM +0300, Kirill Tkhai wrote:
> Using the preparations made in previous patches, in case of memcg
> shrink, we may avoid shrinkers, which are not set in memcg's shrinkers
> bitmap. To do that, we separate iterations over memcg-aware and
> !memcg-aware shrinkers, and memcg-aware shrinkers are chosen
> via for_each_set_bit() from the bitmap. In case of big nodes,
> having many isolated environments, this gives significant
> performance growth. See next patches for the details.
>
> Note, that the patch does not respect to empty memcg shrinkers,
> since we never clear the bitmap bits after we set it once.
> Their shrinkers will be called again, with no shrinked objects
> as result. This functionality is provided by next patches.
>
> Signed-off-by: Kirill Tkhai <ktkhai@virtuozzo.com>
> ---
> mm/vmscan.c | 87 +++++++++++++++++++++++++++++++++++++++++++++++++++++------
> 1 file changed, 78 insertions(+), 9 deletions(-)
>
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index f09ea20d7270..2fbf3b476601 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -373,6 +373,20 @@ int prealloc_shrinker(struct shrinker *shrinker)
> goto free_deferred;
> }
>
> + /*
> + * There is a window between prealloc_shrinker()
> + * and register_shrinker_prepared(). We don't want
> + * to clear bit of a shrinker in such the state
> + * in shrink_slab_memcg(), since this will impose
> + * restrictions on a code registering a shrinker
> + * (they would have to guarantee, their LRU lists
> + * are empty till shrinker is completely registered).
> + * So, we differ the situation, when 1)a shrinker
> + * is semi-registered (id is assigned, but it has
> + * not yet linked to shrinker_list) and 2)shrinker
> + * is not registered (id is not assigned).
> + */
> + INIT_LIST_HEAD(&shrinker->list);
> return 0;
>
> free_deferred:
> @@ -544,6 +558,67 @@ static unsigned long do_shrink_slab(struct shrink_control *shrinkctl,
> return freed;
> }
>
> +#ifdef CONFIG_MEMCG_KMEM
> +static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int nid,
> + struct mem_cgroup *memcg, int priority)
> +{
> + struct memcg_shrinker_map *map;
> + unsigned long freed = 0;
> + int ret, i;
> +
> + if (!memcg_kmem_enabled() || !mem_cgroup_online(memcg))
> + return 0;
> +
> + if (!down_read_trylock(&shrinker_rwsem))
> + return 0;
> +
> + /*
> + * 1) Caller passes only alive memcg, so map can't be NULL.
> + * 2) shrinker_rwsem protects from maps expanding.
> + */
> + map = rcu_dereference_protected(memcg->nodeinfo[nid]->shrinker_map,
> + true);
> + BUG_ON(!map);
> +
> + for_each_set_bit(i, map->map, memcg_shrinker_nr_max) {
> + struct shrink_control sc = {
> + .gfp_mask = gfp_mask,
> + .nid = nid,
> + .memcg = memcg,
> + };
> + struct shrinker *shrinker;
> +
> + shrinker = idr_find(&shrinker_idr, i);
> + if (unlikely(!shrinker)) {

Nit: I don't think 'unlikely' is required here as this is definitely not
a hot path.

> + clear_bit(i, map->map);
> + continue;
> + }
> + BUG_ON(!(shrinker->flags & SHRINKER_MEMCG_AWARE));
> +
> + /* See comment in prealloc_shrinker() */
> + if (unlikely(list_empty(&shrinker->list)))

Ditto.

> + continue;
> +
> + ret = do_shrink_slab(&sc, shrinker, priority);
> + freed += ret;
> +
> + if (rwsem_is_contended(&shrinker_rwsem)) {
> + freed = freed ? : 1;
> + break;
> + }
> + }
> +
> + up_read(&shrinker_rwsem);
> + return freed;
> +}
> +#else /* CONFIG_MEMCG_KMEM */
> +static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int nid,
> + struct mem_cgroup *memcg, int priority)
> +{
> + return 0;
> +}
> +#endif /* CONFIG_MEMCG_KMEM */
> +
> /**
> * shrink_slab - shrink slab caches
> * @gfp_mask: allocation context
> @@ -573,8 +648,8 @@ static unsigned long shrink_slab(gfp_t gfp_mask, int nid,
> struct shrinker *shrinker;
> unsigned long freed = 0;
>
> - if (memcg && (!memcg_kmem_enabled() || !mem_cgroup_online(memcg)))
> - return 0;
> + if (memcg && !mem_cgroup_is_root(memcg))
> + return shrink_slab_memcg(gfp_mask, nid, memcg, priority);
>
> if (!down_read_trylock(&shrinker_rwsem))
> goto out;
> @@ -586,13 +661,7 @@ static unsigned long shrink_slab(gfp_t gfp_mask, int nid,
> .memcg = memcg,
> };
>
> - /*
> - * If kernel memory accounting is disabled, we ignore
> - * SHRINKER_MEMCG_AWARE flag and call all shrinkers
> - * passing NULL for memcg.
> - */
> - if (memcg_kmem_enabled() &&
> - !!memcg != !!(shrinker->flags & SHRINKER_MEMCG_AWARE))
> + if (!!memcg != !!(shrinker->flags & SHRINKER_MEMCG_AWARE))
> continue;
>
> if (!(shrinker->flags & SHRINKER_NUMA_AWARE))
>

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