[PATCH v4 03/17] fs: introduce alloc_inode_sb() to allocate filesystems specific inode

[Muchun Song <songmuchun@bytedance.com>]

The allocated inode cache is supposed to be added to its memcg list_lru
which should be allocated as well in advance. That can be done by
kmem_cache_alloc_lru() which allocates object and list_lru. The file
systems is main user of it. So introduce alloc_inode_sb() to allocate
file system specific inodes and set up the inode reclaim context
properly. The file system is supposed to use alloc_inode_sb() to
allocate inodes. In the later patches, we will convert all users to the
new API.

Signed-off-by: Muchun Song <songmuchun@bytedance.com>
---
 Documentation/filesystems/porting.rst |  5 +++++
 fs/inode.c                            |  2 +-
 include/linux/fs.h                    | 11 +++++++++++
 3 files changed, 17 insertions(+), 1 deletion(-)

diff --git a/Documentation/filesystems/porting.rst b/Documentation/filesystems/porting.rst
index bf19fd6b86e7..c9c157d7b7bb 100644
--- a/Documentation/filesystems/porting.rst
+++ b/Documentation/filesystems/porting.rst
@@ -45,6 +45,11 @@ typically between calling iget_locked() and unlocking the inode.
 
 At some point that will become mandatory.
 
+**mandatory**
+
+The foo_inode_info should always be allocated through alloc_inode_sb() rather
+than kmem_cache_alloc() or kmalloc() related.
+
 ---
 
 **mandatory**
diff --git a/fs/inode.c b/fs/inode.c
index 6b80a51129d5..dcb1e6cad201 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -234,7 +234,7 @@ static struct inode *alloc_inode(struct super_block *sb)
 	if (ops->alloc_inode)
 		inode = ops->alloc_inode(sb);
 	else
-		inode = kmem_cache_alloc(inode_cachep, GFP_KERNEL);
+		inode = alloc_inode_sb(sb, inode_cachep, GFP_KERNEL);
 
 	if (!inode)
 		return NULL;
diff --git a/include/linux/fs.h b/include/linux/fs.h
index bbf812ce89a8..4592f00ec5e7 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -41,6 +41,7 @@
 #include <linux/stddef.h>
 #include <linux/mount.h>
 #include <linux/cred.h>
+#include <linux/slab.h>
 
 #include <asm/byteorder.h>
 #include <uapi/linux/fs.h>
@@ -3178,6 +3179,16 @@ extern void free_inode_nonrcu(struct inode *inode);
 extern int should_remove_suid(struct dentry *);
 extern int file_remove_privs(struct file *);
 
+/*
+ * This must be used for allocating filesystems specific inodes to set
+ * up the inode reclaim context correctly.
+ */
+static inline void *
+alloc_inode_sb(struct super_block *sb, struct kmem_cache *cache, gfp_t gfp)
+{
+	return kmem_cache_alloc_lru(cache, &sb->s_inode_lru, gfp);
+}
+
 extern void __insert_inode_hash(struct inode *, unsigned long hashval);
 static inline void insert_inode_hash(struct inode *inode)
 {
-- 
2.11.0