[PATCH v2 1/3] vfs: introduce reclaim_icache_sb() and reclaim_dcache_sb() helper

[Ye Bin <yebin@huaweicloud.com>]

From: Ye Bin <yebin10@huawei.com>

This patch is prepare for support drop_caches for specify file system.
reclaim_icache_sb()/reclaim_dcache_sb() helper walk the superblock
inode/dentry LRU for freeable inodes/dentrys and attempt to free them.

Signed-off-by: Ye Bin <yebin10@huawei.com>
---
 fs/dcache.c            | 22 ++++++++++++++++++++++
 fs/inode.c             | 21 +++++++++++++++++++++
 fs/internal.h          |  1 +
 include/linux/dcache.h |  1 +
 4 files changed, 45 insertions(+)

diff --git a/fs/dcache.c b/fs/dcache.c
index de3e4e9777ea..d1b29b0f9062 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -1263,6 +1263,28 @@ void shrink_dcache_sb(struct super_block *sb)
 }
 EXPORT_SYMBOL(shrink_dcache_sb);
 
+/**
+ * reclaim_dcache_sb - reclaim dcache for a superblock
+ * @sb: superblock
+ *
+ * Reclaim the dcache for the specified super block. This is used to free
+ * the dcache via sysctl 'drop_fs_caches'.
+ */
+void reclaim_dcache_sb(struct super_block *sb)
+{
+	unsigned long count = list_lru_count(&sb->s_dentry_lru);
+
+	while (count > 0) {
+		LIST_HEAD(dispose);
+		unsigned long nr_to_walk = count >= 1024 ? 1024 : count;
+
+		count -= nr_to_walk;
+		list_lru_walk(&sb->s_dentry_lru, dentry_lru_isolate, &dispose,
+			      nr_to_walk);
+		shrink_dentry_list(&dispose);
+	}
+}
+
 /**
  * enum d_walk_ret - action to talke during tree walk
  * @D_WALK_CONTINUE:	contrinue walk
diff --git a/fs/inode.c b/fs/inode.c
index 7901c2896d78..325de5a51955 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -1073,6 +1073,27 @@ long prune_icache_sb(struct super_block *sb, struct shrink_control *sc)
 	return freed;
 }
 
+/*
+ * Walk the superblock inode LRU for freeable inodes and attempt to free them.
+ * Inodes to be freed are moved to a temporary list and then are freed outside
+ * inode_lock by dispose_list(). This is used to free the icache via sysctl
+ * 'drop_fs_caches'.
+ */
+void reclaim_icache_sb(struct super_block *sb)
+{
+	unsigned long count = list_lru_count(&sb->s_inode_lru);
+
+	while (count > 0) {
+		LIST_HEAD(dispose);
+		unsigned long nr_to_walk = count >= 1024 ? 1024 : count;
+
+		count -= nr_to_walk;
+		list_lru_walk(&sb->s_inode_lru, inode_lru_isolate, &dispose,
+			      nr_to_walk);
+		dispose_list(&dispose);
+	}
+}
+
 static void __wait_on_freeing_inode(struct inode *inode, bool is_inode_hash_locked);
 /*
  * Called with the inode lock held.
diff --git a/fs/internal.h b/fs/internal.h
index 9b2b4d116880..8d3101232fb4 100644
--- a/fs/internal.h
+++ b/fs/internal.h
@@ -204,6 +204,7 @@ extern int vfs_open(const struct path *, struct file *);
  * inode.c
  */
 extern long prune_icache_sb(struct super_block *sb, struct shrink_control *sc);
+extern void reclaim_icache_sb(struct super_block *sb);
 int dentry_needs_remove_privs(struct mnt_idmap *, struct dentry *dentry);
 bool in_group_or_capable(struct mnt_idmap *idmap,
 			 const struct inode *inode, vfsgid_t vfsgid);
diff --git a/include/linux/dcache.h b/include/linux/dcache.h
index c83e02b94389..fed46f694f54 100644
--- a/include/linux/dcache.h
+++ b/include/linux/dcache.h
@@ -257,6 +257,7 @@ extern struct dentry *d_find_any_alias(struct inode *inode);
 extern struct dentry * d_obtain_alias(struct inode *);
 extern struct dentry * d_obtain_root(struct inode *);
 extern void shrink_dcache_sb(struct super_block *);
+extern void reclaim_dcache_sb(struct super_block *sb);
 extern void shrink_dcache_parent(struct dentry *);
 extern void d_invalidate(struct dentry *);
 
-- 
2.34.1