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From:   Yang Shi <shy828301@gmail.com>
To:     guro@fb.com, ktkhai@virtuozzo.com, shakeelb@google.com,
        david@fromorbit.com, hannes@cmpxchg.org, mhocko@suse.com,
        akpm@linux-foundation.org
Cc:     shy828301@gmail.com, linux-mm@kvack.org,
        linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: [v4 PATCH 09/11] mm: vmscan: don't need allocate shrinker->nr_deferred for memcg aware shrinkers
Date:   Thu, 21 Jan 2021 15:06:19 -0800
Message-Id: <20210121230621.654304-10-shy828301@gmail.com>
In-Reply-To: <20210121230621.654304-1-shy828301@gmail.com>
References: <20210121230621.654304-1-shy828301@gmail.com>
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Now nr_deferred is available on per memcg level for memcg aware shrinkers, so don't need
allocate shrinker->nr_deferred for such shrinkers anymore.

The prealloc_memcg_shrinker() would return -ENOSYS if !CONFIG_MEMCG or memcg is disabled
by kernel command line, then shrinker's SHRINKER_MEMCG_AWARE flag would be cleared.
This makes the implementation of this patch simpler.

Signed-off-by: Yang Shi <shy828301@gmail.com>
---
 mm/vmscan.c | 33 ++++++++++++++++++---------------
 1 file changed, 18 insertions(+), 15 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index d8e77ea13815..ea1402e7b968 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -329,6 +329,9 @@ static int prealloc_memcg_shrinker(struct shrinker *shrinker)
 {
 	int id, ret = -ENOMEM;
 
+	if (mem_cgroup_disabled())
+		return -ENOSYS;
+
 	down_write(&shrinker_rwsem);
 	/* This may call shrinker, so it must use down_read_trylock() */
 	id = idr_alloc(&shrinker_idr, NULL, 0, 0, GFP_KERNEL);
@@ -411,7 +414,7 @@ static bool writeback_throttling_sane(struct scan_control *sc)
 #else
 static int prealloc_memcg_shrinker(struct shrinker *shrinker)
 {
-	return 0;
+	return -ENOSYS;
 }
 
 static void unregister_memcg_shrinker(struct shrinker *shrinker)
@@ -522,8 +525,20 @@ unsigned long lruvec_lru_size(struct lruvec *lruvec, enum lru_list lru, int zone
  */
 int prealloc_shrinker(struct shrinker *shrinker)
 {
-	unsigned int size = sizeof(*shrinker->nr_deferred);
+	unsigned int size;
+	int err;
+
+	if (shrinker->flags & SHRINKER_MEMCG_AWARE) {
+		err = prealloc_memcg_shrinker(shrinker);
+		if (!err)
+			return 0;
+		if (err != -ENOSYS)
+			return err;
+
+		shrinker->flags &= ~SHRINKER_MEMCG_AWARE;
+	}
 
+	size = sizeof(*shrinker->nr_deferred);
 	if (shrinker->flags & SHRINKER_NUMA_AWARE)
 		size *= nr_node_ids;
 
@@ -531,26 +546,14 @@ int prealloc_shrinker(struct shrinker *shrinker)
 	if (!shrinker->nr_deferred)
 		return -ENOMEM;
 
-	if (shrinker->flags & SHRINKER_MEMCG_AWARE) {
-		if (prealloc_memcg_shrinker(shrinker))
-			goto free_deferred;
-	}
 
 	return 0;
-
-free_deferred:
-	kfree(shrinker->nr_deferred);
-	shrinker->nr_deferred = NULL;
-	return -ENOMEM;
 }
 
 void free_prealloced_shrinker(struct shrinker *shrinker)
 {
-	if (!shrinker->nr_deferred)
-		return;
-
 	if (shrinker->flags & SHRINKER_MEMCG_AWARE)
-		unregister_memcg_shrinker(shrinker);
+		return unregister_memcg_shrinker(shrinker);
 
 	kfree(shrinker->nr_deferred);
 	shrinker->nr_deferred = NULL;
-- 
2.26.2