[PATCH v5 3/3] exfat: reclaim name filters under memory pressure

[Yang Wen <anmuxixixi@gmail.com>]

Each active large directory can hold a 64 KiB name filter. Add a
per-superblock LRU and shrinker so filters can be reclaimed when memory is
tight.

Signed-off-by: Yang Wen <anmuxixixi@gmail.com>
---
 fs/exfat/dir.c      | 145 +++++++++++++++++++++++++++++++++++++++++++-
 fs/exfat/exfat_fs.h |  10 +++
 fs/exfat/super.c    |   8 +++
 3 files changed, 160 insertions(+), 3 deletions(-)

diff --git a/fs/exfat/dir.c b/fs/exfat/dir.c
index 08b7a50de871..013b7e43a289 100644
--- a/fs/exfat/dir.c
+++ b/fs/exfat/dir.c
@@ -9,6 +9,7 @@
 #include <linux/buffer_head.h>
 #include <linux/filelock.h>
 #include <linux/hash.h>
+#include <linux/shrinker.h>
 #include <linux/stringhash.h>
 
 #include "exfat_raw.h"
@@ -91,12 +92,144 @@ static void exfat_name_filter_indexes(struct super_block *sb,
 			     EXFAT_NAME_FILTER_ORDER);
 }
 
+static unsigned long *
+exfat_name_filter_detach_locked(struct exfat_sb_info *sbi,
+				struct exfat_inode_info *ei)
+{
+	unsigned long *filter = ei->name_filter;
+
+	if (!filter)
+		return NULL;
+
+	ei->name_filter = NULL;
+	list_del_init(&ei->name_filter_lru);
+	sbi->name_filter_count--;
+	return filter;
+}
+
+static void exfat_name_filter_touch(struct exfat_inode_info *ei)
+{
+	struct exfat_sb_info *sbi = EXFAT_SB(ei->vfs_inode.i_sb);
+
+	spin_lock(&sbi->name_filter_lock);
+	if (ei->name_filter)
+		list_move_tail(&ei->name_filter_lru, &sbi->name_filter_lru);
+	spin_unlock(&sbi->name_filter_lock);
+}
+
 void exfat_name_filter_free(struct inode *inode)
 {
 	struct exfat_inode_info *ei = EXFAT_I(inode);
+	struct exfat_sb_info *sbi;
+	unsigned long *filter;
 
-	kvfree(ei->name_filter);
-	ei->name_filter = NULL;
+	if (!READ_ONCE(ei->name_filter))
+		return;
+
+	sbi = EXFAT_SB(inode->i_sb);
+	spin_lock(&sbi->name_filter_lock);
+	filter = exfat_name_filter_detach_locked(sbi, ei);
+	spin_unlock(&sbi->name_filter_lock);
+	kvfree(filter);
+}
+
+static unsigned long
+exfat_name_filter_count_objects(struct shrinker *shrinker,
+				struct shrink_control *sc)
+{
+	struct exfat_sb_info *sbi = shrinker->private_data;
+	unsigned long count;
+
+	spin_lock(&sbi->name_filter_lock);
+	count = sbi->name_filter_count;
+	spin_unlock(&sbi->name_filter_lock);
+
+	return count ? count : SHRINK_EMPTY;
+}
+
+static unsigned long
+exfat_name_filter_scan_objects(struct shrinker *shrinker,
+			       struct shrink_control *sc)
+{
+	struct exfat_sb_info *sbi = shrinker->private_data;
+	unsigned long freed = 0;
+
+	/* Avoid reclaim recursion from a GFP_NOFS allocation under s_lock. */
+	if (!mutex_trylock(&sbi->s_lock)) {
+		sc->nr_scanned = 0;
+		return SHRINK_STOP;
+	}
+
+	while (freed < sc->nr_to_scan) {
+		struct exfat_inode_info *ei;
+		unsigned long *filter;
+
+		spin_lock(&sbi->name_filter_lock);
+		if (list_empty(&sbi->name_filter_lru)) {
+			spin_unlock(&sbi->name_filter_lock);
+			break;
+		}
+
+		ei = list_first_entry(&sbi->name_filter_lru,
+				      struct exfat_inode_info,
+				      name_filter_lru);
+		filter = exfat_name_filter_detach_locked(sbi, ei);
+		spin_unlock(&sbi->name_filter_lock);
+
+		kvfree(filter);
+		freed++;
+		cond_resched();
+	}
+
+	mutex_unlock(&sbi->s_lock);
+	sc->nr_scanned = freed;
+	return freed;
+}
+
+void exfat_name_filter_shrinker_register(struct super_block *sb)
+{
+	struct exfat_sb_info *sbi = EXFAT_SB(sb);
+	struct shrinker *shrinker;
+
+	shrinker = shrinker_alloc(SHRINKER_NONSLAB,
+				  "exfat-name-filter:%s", sb->s_id);
+	if (!shrinker) {
+		exfat_warn(sb, "failed to allocate name filter shrinker");
+		return;
+	}
+
+	shrinker->count_objects = exfat_name_filter_count_objects;
+	shrinker->scan_objects = exfat_name_filter_scan_objects;
+	shrinker->private_data = sbi;
+	shrinker_register(shrinker);
+	sbi->name_filter_shrinker = shrinker;
+}
+
+void exfat_name_filter_shrinker_unregister(struct super_block *sb)
+{
+	struct exfat_sb_info *sbi = EXFAT_SB(sb);
+	struct shrinker *shrinker = sbi->name_filter_shrinker;
+
+	sbi->name_filter_shrinker = NULL;
+	shrinker_free(shrinker);
+
+	for (;;) {
+		struct exfat_inode_info *ei;
+		unsigned long *filter;
+
+		spin_lock(&sbi->name_filter_lock);
+		if (list_empty(&sbi->name_filter_lru)) {
+			spin_unlock(&sbi->name_filter_lock);
+			break;
+		}
+
+		ei = list_first_entry(&sbi->name_filter_lru,
+				      struct exfat_inode_info,
+				      name_filter_lru);
+		filter = exfat_name_filter_detach_locked(sbi, ei);
+		spin_unlock(&sbi->name_filter_lock);
+		kvfree(filter);
+	}
 }
 
 bool exfat_name_filter_maybe_contains(struct inode *inode,
@@ -108,6 +241,7 @@ bool exfat_name_filter_maybe_contains(struct inode *inode,
 	if (!ei->name_filter)
 		return true;
 
+	exfat_name_filter_touch(ei);
 	exfat_name_filter_indexes(inode->i_sb, name, indexes);
 	return test_bit(indexes[0], ei->name_filter) &&
 	       test_bit(indexes[1], ei->name_filter) &&
@@ -123,6 +257,7 @@ void exfat_name_filter_add(struct inode *inode,
 	if (!ei->name_filter)
 		return;
 
+	exfat_name_filter_touch(ei);
 	exfat_name_filter_indexes(inode->i_sb, name, indexes);
 	__set_bit(indexes[0], ei->name_filter);
 	__set_bit(indexes[1], ei->name_filter);
@@ -145,7 +280,7 @@ static void exfat_build_name_filter(struct super_block *sb,
 	struct exfat_sb_info *sbi = EXFAT_SB(sb);
 	int i;
 
-	if (ei->name_filter ||
+	if (!sbi->name_filter_shrinker || ei->name_filter ||
 	    exfat_bytes_to_dentries(i_size_read(inode)) <
 					EXFAT_NAME_FILTER_MIN_DENTRIES)
 		return;
@@ -195,7 +330,11 @@ static void exfat_build_name_filter(struct super_block *sb,
 	}
 
 complete:
+	spin_lock(&sbi->name_filter_lock);
 	ei->name_filter = filter;
+	list_add_tail(&ei->name_filter_lru, &sbi->name_filter_lru);
+	sbi->name_filter_count++;
+	spin_unlock(&sbi->name_filter_lock);
 	return;
 abort:
 	kvfree(filter);
diff --git a/fs/exfat/exfat_fs.h b/fs/exfat/exfat_fs.h
index 3bbfa7092c0d..b3edb6fdfca6 100644
--- a/fs/exfat/exfat_fs.h
+++ b/fs/exfat/exfat_fs.h
@@ -14,6 +14,8 @@
 #include <uapi/linux/exfat.h>
 #include <linux/buffer_head.h>
 
+struct shrinker;
+
 #define EXFAT_ROOT_INO		1
 
 /*
@@ -263,6 +265,11 @@ struct exfat_sb_info {
 
 	spinlock_t inode_hash_lock;
 	struct hlist_head inode_hashtable[EXFAT_HASH_SIZE];
+	/* Protects name_filter_lru and name_filter_count. */
+	spinlock_t name_filter_lock;
+	struct list_head name_filter_lru;
+	unsigned long name_filter_count;
+	struct shrinker *name_filter_shrinker;
 	struct rcu_head rcu;
 };
 
@@ -294,6 +301,7 @@ struct exfat_inode_info {
 	struct exfat_hint_femp hint_femp;
 	/* Complete, in-memory Bloom filter of directory names */
 	unsigned long *name_filter;
+	struct list_head name_filter_lru;
 
 	spinlock_t cache_lru_lock;
 	struct list_head cache_lru;
@@ -635,6 +643,8 @@ bool exfat_name_filter_maybe_contains(struct inode *inode,
 void exfat_name_filter_add(struct inode *inode,
 			   const struct exfat_uni_name *name);
 void exfat_name_filter_free(struct inode *inode);
+void exfat_name_filter_shrinker_register(struct super_block *sb);
+void exfat_name_filter_shrinker_unregister(struct super_block *sb);
 
 static inline int exfat_chain_advance(struct super_block *sb,
 		struct exfat_chain *chain, unsigned int step)
diff --git a/fs/exfat/super.c b/fs/exfat/super.c
index 4924f0fad836..465e33c9ba49 100644
--- a/fs/exfat/super.c
+++ b/fs/exfat/super.c
@@ -46,6 +46,7 @@ static void exfat_put_super(struct super_block *sb)
 {
 	struct exfat_sb_info *sbi = EXFAT_SB(sb);
 
+	exfat_name_filter_shrinker_unregister(sb);
 	mutex_lock(&sbi->s_lock);
 	exfat_clear_volume_dirty(sb);
 	exfat_free_bitmap(sbi);
@@ -210,6 +211,7 @@ static struct inode *exfat_alloc_inode(struct super_block *sb)
 		return NULL;
 
 	ei->name_filter = NULL;
+	INIT_LIST_HEAD(&ei->name_filter_lru);
 	return &ei->vfs_inode;
 }
 
@@ -746,6 +748,8 @@ static int exfat_fill_super(struct super_block *sb, struct fs_context *fc)
 		goto free_table;
 	}
 
+	exfat_name_filter_shrinker_register(sb);
+
 	return 0;
 
 put_inode:
@@ -845,6 +849,10 @@ static int exfat_init_fs_context(struct fs_context *fc)
 
 	mutex_init(&sbi->s_lock);
 	mutex_init(&sbi->bitmap_lock);
+	spin_lock_init(&sbi->name_filter_lock);
+	INIT_LIST_HEAD(&sbi->name_filter_lru);
+	sbi->name_filter_count = 0;
+	sbi->name_filter_shrinker = NULL;
 	ratelimit_state_init(&sbi->ratelimit, DEFAULT_RATELIMIT_INTERVAL,
 			DEFAULT_RATELIMIT_BURST);
 
-- 
2.34.1