[v2 PATCH 4/9] mm: vmscan: use a new flag to indicate shrinker is registered

Yang Shi
2020-12-14T22:37:52Z

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.

Introduce a new flag to indicate if shrinker is registered or not.

Signed-off-by: Yang Shi <shy828301@gmail.com>
---
include/linux/shrinker.h | 7 ++++---
mm/vmscan.c | 13 +++++++++----
2 files changed, 13 insertions(+), 7 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 9b31b9c419ec..16c9d2aeeb26 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -378,6 +378,7 @@ void register_shrinker_prepared(struct shrinker *shrinker)
if (shrinker->flags & SHRINKER_MEMCG_AWARE)
idr_replace(&shrinker_idr, shrinker, shrinker->id);
#endif
+ shrinker->flags |= SHRINKER_REGISTERED;
up_write(&shrinker_rwsem);
}

@@ -397,13 +398,17 @@ EXPORT_SYMBOL(register_shrinker);
*/
void unregister_shrinker(struct shrinker *shrinker)
{
- if (!shrinker->nr_deferred)
- return;
- if (shrinker->flags & SHRINKER_MEMCG_AWARE)
- unregister_memcg_shrinker(shrinker);
down_write(&shrinker_rwsem);
+ if (!(shrinker->flags & SHRINKER_REGISTERED)) {
+ up_write(&shrinker_rwsem);
+ return;
+ }
list_del(&shrinker->list);
+ shrinker->flags &= ~SHRINKER_REGISTERED;
up_write(&shrinker_rwsem);
+
+ if (shrinker->flags & SHRINKER_MEMCG_AWARE)
+ unregister_memcg_shrinker(shrinker);
kfree(shrinker->nr_deferred);
shrinker->nr_deferred = NULL;
}
--
2.26.2