[069/143] mm: vmscan: use a new flag to indicate shrinker is registered

Commit Message

Andrew Morton May 5, 2021, 1:36 a.m. UTC

From: Yang Shi <[e-mail]>
Subject: 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/[e-mail]
Signed-off-by: Yang Shi <[e-mail]>
Acked-by: Kirill Tkhai <[e-mail]>
Acked-by: Vlastimil Babka <[e-mail]>
Acked-by: Roman Gushchin <[e-mail]>
Reviewed-by: Shakeel Butt <[e-mail]>
Cc: Dave Chinner <[e-mail]>
Cc: Johannes Weiner <[e-mail]>
Cc: Michal Hocko <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
---

 include/linux/shrinker.h |    7 +++---
 mm/vmscan.c              |   40 +++++++++++++------------------------
 2 files changed, 19 insertions(+), 28 deletions(-)

Patch

--- a/include/linux/shrinker.h~mm-vmscan-use-a-new-flag-to-indicate-shrinker-is-registered
+++ a/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);
--- a/mm/vmscan.c~mm-vmscan-use-a-new-flag-to-indicate-shrinker-is-registered
+++ a/mm/vmscan.c
@@ -316,19 +316,6 @@  void set_shrinker_bit(struct mem_cgroup
 	}
 }
 
-/*
- * 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(struc
 
 	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(st
 
 	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 shr
 	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 s
 {
 	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(g
 		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;