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Date: Tue, 16 Feb 2021 18:00:33 -0800
From: Roman Gushchin <guro@...com>
To: Yang Shi <shy828301@...il.com>
CC: <ktkhai@...tuozzo.com>, <vbabka@...e.cz>, <shakeelb@...gle.com>,
<david@...morbit.com>, <hannes@...xchg.org>, <mhocko@...e.com>,
<akpm@...ux-foundation.org>, <linux-mm@...ck.org>,
<linux-fsdevel@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [v8 PATCH 08/13] mm: vmscan: use a new flag to indicate shrinker
is registered
On Tue, Feb 16, 2021 at 04:13:17PM -0800, Yang Shi wrote:
> Currently registered shrinker is indicated by non-NULL shrinker->nr_deferred.
> This approach is fine with nr_deferred at the shrinker level, but the following
> patches will move MEMCG_AWARE shrinkers' nr_deferred to memcg level, so their
> shrinker->nr_deferred would always be NULL. This would prevent the shrinkers
> from unregistering correctly.
>
> Remove SHRINKER_REGISTERING since we could check if shrinker is registered
> successfully by the new flag.
>
> Acked-by: Kirill Tkhai <ktkhai@...tuozzo.com>
> Acked-by: Vlastimil Babka <vbabka@...e.cz>
> Signed-off-by: Yang Shi <shy828301@...il.com>
Acked-by: Roman Gushchin <guro@...com>
> ---
> include/linux/shrinker.h | 7 ++++---
> mm/vmscan.c | 40 +++++++++++++++-------------------------
> 2 files changed, 19 insertions(+), 28 deletions(-)
>
> diff --git a/include/linux/shrinker.h b/include/linux/shrinker.h
> index 0f80123650e2..1eac79ce57d4 100644
> --- a/include/linux/shrinker.h
> +++ b/include/linux/shrinker.h
> @@ -79,13 +79,14 @@ struct shrinker {
> #define DEFAULT_SEEKS 2 /* A good number if you don't know better. */
>
> /* Flags */
> -#define SHRINKER_NUMA_AWARE (1 << 0)
> -#define SHRINKER_MEMCG_AWARE (1 << 1)
> +#define SHRINKER_REGISTERED (1 << 0)
> +#define SHRINKER_NUMA_AWARE (1 << 1)
> +#define SHRINKER_MEMCG_AWARE (1 << 2)
> /*
> * It just makes sense when the shrinker is also MEMCG_AWARE for now,
> * non-MEMCG_AWARE shrinker should not have this flag set.
> */
> -#define SHRINKER_NONSLAB (1 << 2)
> +#define SHRINKER_NONSLAB (1 << 3)
>
> extern int prealloc_shrinker(struct shrinker *shrinker);
> extern void register_shrinker_prepared(struct shrinker *shrinker);
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index fe6e25f46b55..a1047ea60ecf 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -314,19 +314,6 @@ void set_shrinker_bit(struct mem_cgroup *memcg, int nid, int shrinker_id)
> }
> }
>
> -/*
> - * We allow subsystems to populate their shrinker-related
> - * LRU lists before register_shrinker_prepared() is called
> - * for the shrinker, since we don't want to impose
> - * restrictions on their internal registration order.
> - * In this case shrink_slab_memcg() may find corresponding
> - * bit is set in the shrinkers map.
> - *
> - * This value is used by the function to detect registering
> - * shrinkers and to skip do_shrink_slab() calls for them.
> - */
> -#define SHRINKER_REGISTERING ((struct shrinker *)~0UL)
> -
> static DEFINE_IDR(shrinker_idr);
>
> static int prealloc_memcg_shrinker(struct shrinker *shrinker)
> @@ -335,7 +322,7 @@ static int prealloc_memcg_shrinker(struct shrinker *shrinker)
>
> down_write(&shrinker_rwsem);
> /* This may call shrinker, so it must use down_read_trylock() */
> - id = idr_alloc(&shrinker_idr, SHRINKER_REGISTERING, 0, 0, GFP_KERNEL);
> + id = idr_alloc(&shrinker_idr, shrinker, 0, 0, GFP_KERNEL);
> if (id < 0)
> goto unlock;
>
> @@ -358,9 +345,9 @@ static void unregister_memcg_shrinker(struct shrinker *shrinker)
>
> BUG_ON(id < 0);
>
> - down_write(&shrinker_rwsem);
> + lockdep_assert_held(&shrinker_rwsem);
> +
> idr_remove(&shrinker_idr, id);
> - up_write(&shrinker_rwsem);
> }
>
> static bool cgroup_reclaim(struct scan_control *sc)
> @@ -487,8 +474,11 @@ void free_prealloced_shrinker(struct shrinker *shrinker)
> if (!shrinker->nr_deferred)
> return;
>
> - if (shrinker->flags & SHRINKER_MEMCG_AWARE)
> + if (shrinker->flags & SHRINKER_MEMCG_AWARE) {
> + down_write(&shrinker_rwsem);
> unregister_memcg_shrinker(shrinker);
> + up_write(&shrinker_rwsem);
> + }
>
> kfree(shrinker->nr_deferred);
> shrinker->nr_deferred = NULL;
> @@ -498,10 +488,7 @@ void register_shrinker_prepared(struct shrinker *shrinker)
> {
> down_write(&shrinker_rwsem);
> list_add_tail(&shrinker->list, &shrinker_list);
> -#ifdef CONFIG_MEMCG
> - if (shrinker->flags & SHRINKER_MEMCG_AWARE)
> - idr_replace(&shrinker_idr, shrinker, shrinker->id);
> -#endif
> + shrinker->flags |= SHRINKER_REGISTERED;
> up_write(&shrinker_rwsem);
> }
>
> @@ -521,13 +508,16 @@ EXPORT_SYMBOL(register_shrinker);
> */
> void unregister_shrinker(struct shrinker *shrinker)
> {
> - if (!shrinker->nr_deferred)
> + if (!(shrinker->flags & SHRINKER_REGISTERED))
> return;
> - if (shrinker->flags & SHRINKER_MEMCG_AWARE)
> - unregister_memcg_shrinker(shrinker);
> +
> down_write(&shrinker_rwsem);
> list_del(&shrinker->list);
> + shrinker->flags &= ~SHRINKER_REGISTERED;
> + if (shrinker->flags & SHRINKER_MEMCG_AWARE)
> + unregister_memcg_shrinker(shrinker);
> up_write(&shrinker_rwsem);
> +
> kfree(shrinker->nr_deferred);
> shrinker->nr_deferred = NULL;
> }
> @@ -692,7 +682,7 @@ static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int nid,
> struct shrinker *shrinker;
>
> shrinker = idr_find(&shrinker_idr, i);
> - if (unlikely(!shrinker || shrinker == SHRINKER_REGISTERING)) {
> + if (unlikely(!shrinker || !(shrinker->flags & SHRINKER_REGISTERED))) {
> if (!shrinker)
> clear_bit(i, info->map);
> continue;
> --
> 2.26.2
>
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