linux-kernel - [PATCH v4 3/4] mm: shrinker: remove redundant shrinker

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Message-Id: <20230911092517.64141-4-zhengqi.arch@bytedance.com>
Date:   Mon, 11 Sep 2023 17:25:16 +0800
From:   Qi Zheng <zhengqi.arch@...edance.com>
To:     akpm@...ux-foundation.org, david@...morbit.com, tkhai@...ru,
        vbabka@...e.cz, roman.gushchin@...ux.dev, djwong@...nel.org,
        brauner@...nel.org, paulmck@...nel.org, tytso@....edu,
        steven.price@....com, cel@...nel.org, senozhatsky@...omium.org,
        yujie.liu@...el.com, gregkh@...uxfoundation.org,
        muchun.song@...ux.dev, joel@...lfernandes.org,
        christian.koenig@....com, daniel@...ll.ch
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        dri-devel@...ts.freedesktop.org, linux-fsdevel@...r.kernel.org,
        Qi Zheng <zhengqi.arch@...edance.com>,
        Muchun Song <songmuchun@...edance.com>
Subject: [PATCH v4 3/4] mm: shrinker: remove redundant shrinker_rwsem in debugfs operations

The debugfs_remove_recursive() will wait for debugfs_file_put() to return,
so the shrinker will not be freed when doing debugfs operations (such as
shrinker_debugfs_count_show() and shrinker_debugfs_scan_write()), so there
is no need to hold shrinker_rwsem during debugfs operations.

Signed-off-by: Qi Zheng <zhengqi.arch@...edance.com>
Reviewed-by: Muchun Song <songmuchun@...edance.com>
---
 mm/shrinker_debug.c | 16 +---------------
 1 file changed, 1 insertion(+), 15 deletions(-)

diff --git a/mm/shrinker_debug.c b/mm/shrinker_debug.c
index ee0cddb4530f..e4ce509f619e 100644
--- a/mm/shrinker_debug.c
+++ b/mm/shrinker_debug.c
@@ -51,17 +51,12 @@ static int shrinker_debugfs_count_show(struct seq_file *m, void *v)
 	struct mem_cgroup *memcg;
 	unsigned long total;
 	bool memcg_aware;
-	int ret, nid;
+	int ret = 0, nid;
 
 	count_per_node = kcalloc(nr_node_ids, sizeof(unsigned long), GFP_KERNEL);
 	if (!count_per_node)
 		return -ENOMEM;
 
-	ret = down_read_killable(&shrinker_rwsem);
-	if (ret) {
-		kfree(count_per_node);
-		return ret;
-	}
 	rcu_read_lock();
 
 	memcg_aware = shrinker->flags & SHRINKER_MEMCG_AWARE;
@@ -94,7 +89,6 @@ static int shrinker_debugfs_count_show(struct seq_file *m, void *v)
 	} while ((memcg = mem_cgroup_iter(NULL, memcg, NULL)) != NULL);
 
 	rcu_read_unlock();
-	up_read(&shrinker_rwsem);
 
 	kfree(count_per_node);
 	return ret;
@@ -119,7 +113,6 @@ static ssize_t shrinker_debugfs_scan_write(struct file *file,
 	struct mem_cgroup *memcg = NULL;
 	int nid;
 	char kbuf[72];
-	ssize_t ret;
 
 	read_len = size < (sizeof(kbuf) - 1) ? size : (sizeof(kbuf) - 1);
 	if (copy_from_user(kbuf, buf, read_len))
@@ -148,12 +141,6 @@ static ssize_t shrinker_debugfs_scan_write(struct file *file,
 		return -EINVAL;
 	}
 
-	ret = down_read_killable(&shrinker_rwsem);
-	if (ret) {
-		mem_cgroup_put(memcg);
-		return ret;
-	}
-
 	sc.nid = nid;
 	sc.memcg = memcg;
 	sc.nr_to_scan = nr_to_scan;
@@ -161,7 +148,6 @@ static ssize_t shrinker_debugfs_scan_write(struct file *file,
 
 	shrinker->scan_objects(shrinker, &sc);
 
-	up_read(&shrinker_rwsem);
 	mem_cgroup_put(memcg);
 
 	return size;
-- 
2.30.2