[PATCH v3 04/13] VFS hot tracking: register one shrinker

[zwu.kernel@gmail.com]

From: Zhi Yong Wu <wuzhy@linux.vnet.ibm.com>

  Register a shrinker to control the amount of memory that
is used in tracking hot regions. If we are throwing inodes
out of memory due to memory pressure, we most definitely are
going to need to reduce the amount of memory the tracking
code is using, even if it means losing useful information
That is, the shrinker accelerates the aging process.

Signed-off-by: Chandra Seetharaman <sekharan@us.ibm.com>
Signed-off-by: Zhi Yong Wu <wuzhy@linux.vnet.ibm.com>
---
 fs/hot_tracking.c            | 76 ++++++++++++++++++++++++++++++++++++++++++--
 include/linux/hot_tracking.h |  2 ++
 2 files changed, 76 insertions(+), 2 deletions(-)

diff --git a/fs/hot_tracking.c b/fs/hot_tracking.c
index 50c6820..3f3b656 100644
--- a/fs/hot_tracking.c
+++ b/fs/hot_tracking.c
@@ -103,8 +103,10 @@ static void hot_comm_item_unlink(struct hot_info *root,
 		}
 		spin_unlock(&root->m_lock);
 
-		if (flag)
+		if (flag) {
+			atomic_dec(&root->hot_map_nr);
 			hot_comm_item_put(ci);
+		}
 
 		if (ci->hot_freq_data.flags == TYPE_RANGE) {
 			struct hot_range_item *hr = container_of(ci,
@@ -464,8 +466,10 @@ static bool hot_map_update(struct hot_info *root,
 		}
 		spin_unlock(&root->m_lock);
 
-		if (!flag)
+		if (!flag) {
+			atomic_inc(&root->hot_map_nr);
 			hot_comm_item_get(ci);
+		}
 
 		spin_lock(&root->m_lock);
 		if (test_bit(HOT_DELETING, &ci->delete_flag)) {
@@ -523,6 +527,39 @@ static int hot_temp_cmp(void *priv, struct list_head *a,
 	return 0;
 }
 
+static void hot_item_evictor(struct hot_info *root, unsigned long work,
+			unsigned long (*work_get)(struct hot_info *root))
+{
+	int i;
+
+	if (work <= 0)
+		return;
+
+	for (i = 0; i < MAP_SIZE; i++) {
+		struct hot_comm_item *ci;
+		unsigned long work_prev;
+
+		rcu_read_lock();
+		if (list_empty(&root->hot_map[TYPE_INODE][i])) {
+			rcu_read_unlock();
+			continue;
+		}
+
+		list_for_each_entry_rcu(ci, &root->hot_map[TYPE_INODE][i],
+					track_list) {
+			work_prev = work_get(root);
+			hot_comm_item_unlink(root, ci);
+			work -= (work_prev - work_get(root));
+			if (work <= 0)
+				break;
+		}
+		rcu_read_unlock();
+
+		if (work <= 0)
+			break;
+	}
+}
+
 /*
  * Every sync period we update temperatures for
  * each hot inode item and hot range item for aging
@@ -585,6 +622,34 @@ void __init hot_cache_init(void)
 }
 EXPORT_SYMBOL_GPL(hot_cache_init);
 
+static inline unsigned long hot_nr_get(struct hot_info *root)
+{
+	return (unsigned long)atomic_read(&root->hot_map_nr);
+}
+
+static void hot_prune_map(struct hot_info *root, unsigned long nr)
+{
+	hot_item_evictor(root, nr, hot_nr_get);
+}
+
+/* The shrinker callback function */
+static int hot_track_prune(struct shrinker *shrink,
+			struct shrink_control *sc)
+{
+	struct hot_info *root =
+		container_of(shrink, struct hot_info, hot_shrink);
+
+	if (sc->nr_to_scan == 0)
+		return atomic_read(&root->hot_map_nr) / 2;
+
+	if (!(sc->gfp_mask & __GFP_FS))
+		return -1;
+
+	hot_prune_map(root, sc->nr_to_scan);
+
+	return atomic_read(&root->hot_map_nr);
+}
+
 /*
  * Main function to update i/o access frequencies, and it will be called
  * from read/writepages() hooks, which are read_pages(), do_writepages(),
@@ -649,6 +714,7 @@ static struct hot_info *hot_tree_init(struct super_block *sb)
 	root->hot_inode_tree = RB_ROOT;
 	spin_lock_init(&root->t_lock);
 	spin_lock_init(&root->m_lock);
+	atomic_set(&root->hot_map_nr, 0);
 
 	for (i = 0; i < MAP_SIZE; i++) {
 		for (j = 0; j < MAX_TYPES; j++)
@@ -669,6 +735,11 @@ static struct hot_info *hot_tree_init(struct super_block *sb)
 	queue_delayed_work(root->update_wq, &root->update_work,
 		msecs_to_jiffies(HOT_UPDATE_INTERVAL * MSEC_PER_SEC));
 
+	/* Register a shrinker callback */
+	root->hot_shrink.shrink = hot_track_prune;
+	root->hot_shrink.seeks = DEFAULT_SEEKS;
+	register_shrinker(&root->hot_shrink);
+
 	return root;
 }
 
@@ -680,6 +751,7 @@ static void hot_tree_exit(struct hot_info *root)
 	struct rb_node *node;
 	struct hot_comm_item *ci;
 
+	unregister_shrinker(&root->hot_shrink);
 	cancel_delayed_work_sync(&root->update_work);
 	destroy_workqueue(root->update_wq);
 
diff --git a/include/linux/hot_tracking.h b/include/linux/hot_tracking.h
index 02a9521..8cb7526 100644
--- a/include/linux/hot_tracking.h
+++ b/include/linux/hot_tracking.h
@@ -90,8 +90,10 @@ struct hot_info {
 	spinlock_t t_lock;				/* protect above tree */
 	struct list_head hot_map[MAX_TYPES][MAP_SIZE];	/* map of inode temp */
 	spinlock_t m_lock;
+	atomic_t hot_map_nr;
 	struct workqueue_struct *update_wq;
 	struct delayed_work update_work;
+	struct shrinker hot_shrink;
 };
 
 extern void __init hot_cache_init(void);
-- 
1.7.11.7