mm: vmscan: use a new flag to indicate shrinker is registered

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.

Link: https://lkml.kernel.org/r/20210311190845.9708-9-shy828301@gmail.com
Signed-off-by: Yang Shi <shy828301@gmail.com>
Acked-by: Kirill Tkhai <ktkhai@virtuozzo.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Roman Gushchin <guro@fb.com>
Reviewed-by: Shakeel Butt <shakeelb@google.com>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/include/linux/shrinker.h b/include/linux/shrinker.h
index 0f80123..1eac79c 100644 (file)
--- 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 400f4a6..d160116 100644 (file)
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -316,19 +316,6 @@ 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)
@@ -337,7 +324,7 @@ 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;
 
@@ -360,9 +347,9 @@ 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)
@@ -490,8 +477,11 @@ 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;
@@ -501,10 +491,7 @@ 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);
 }
 
@@ -524,13 +511,16 @@ 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;
 }
@@ -695,7 +685,7 @@ 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;