From:   Qi Zheng <zhengqi.arch@bytedance.com>
To:     akpm@linux-foundation.org, tkhai@ya.ru, hannes@cmpxchg.org,
        shakeelb@google.com, mhocko@kernel.org, roman.gushchin@linux.dev,
        muchun.song@linux.dev, david@redhat.com, shy828301@gmail.com,
        rppt@kernel.org
Cc:     sultan@kerneltoast.com, dave@stgolabs.net,
        penguin-kernel@I-love.SAKURA.ne.jp, paulmck@kernel.org,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        Qi Zheng <zhengqi.arch@bytedance.com>
Subject: [PATCH v4 5/8] mm: shrinkers: make count and scan in shrinker debugfs lockless
Date:   Tue,  7 Mar 2023 14:56:02 +0800
Message-Id: <20230307065605.58209-6-zhengqi.arch@bytedance.com>
In-Reply-To: <20230307065605.58209-1-zhengqi.arch@bytedance.com>
References: <20230307065605.58209-1-zhengqi.arch@bytedance.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

Like global and memcg slab shrink, also use SRCU to
make count and scan operations in memory shrinker
debugfs lockless.

Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
---
 mm/shrinker_debug.c | 24 +++++++-----------------
 1 file changed, 7 insertions(+), 17 deletions(-)

diff --git a/mm/shrinker_debug.c b/mm/shrinker_debug.c
index 39c3491e28a3..6aa7a7ec69da 100644
--- a/mm/shrinker_debug.c
+++ b/mm/shrinker_debug.c
@@ -9,6 +9,7 @@
 /* defined in vmscan.c */
 extern struct rw_semaphore shrinker_rwsem;
 extern struct list_head shrinker_list;
+extern struct srcu_struct shrinker_srcu;
 
 static DEFINE_IDA(shrinker_debugfs_ida);
 static struct dentry *shrinker_debugfs_root;
@@ -49,18 +50,13 @@ 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, srcu_idx;
 
 	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();
+	srcu_idx = srcu_read_lock(&shrinker_srcu);
 
 	memcg_aware = shrinker->flags & SHRINKER_MEMCG_AWARE;
 
@@ -91,8 +87,7 @@ 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);
+	srcu_read_unlock(&shrinker_srcu, srcu_idx);
 
 	kfree(count_per_node);
 	return ret;
@@ -115,9 +110,8 @@ static ssize_t shrinker_debugfs_scan_write(struct file *file,
 		.gfp_mask = GFP_KERNEL,
 	};
 	struct mem_cgroup *memcg = NULL;
-	int nid;
+	int nid, srcu_idx;
 	char kbuf[72];
-	ssize_t ret;
 
 	read_len = size < (sizeof(kbuf) - 1) ? size : (sizeof(kbuf) - 1);
 	if (copy_from_user(kbuf, buf, read_len))
@@ -146,11 +140,7 @@ 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;
-	}
+	srcu_idx = srcu_read_lock(&shrinker_srcu);
 
 	sc.nid = nid;
 	sc.memcg = memcg;
@@ -159,7 +149,7 @@ static ssize_t shrinker_debugfs_scan_write(struct file *file,
 
 	shrinker->scan_objects(shrinker, &sc);
 
-	up_read(&shrinker_rwsem);
+	srcu_read_unlock(&shrinker_srcu, srcu_idx);
 	mem_cgroup_put(memcg);
 
 	return size;
-- 
2.20.1