fs: introduce alloc_inode_sb() to allocate filesystems specific inode

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 later patches, we will convert all users to the new API.

Link: https://lkml.kernel.org/r/20220228122126.37293-4-songmuchun@bytedance.comSigned-off-by: Muchun Song <songmuchun@bytedance.com>
Reviewed-by: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Alex Shi <alexs@kernel.org>
Cc: Anna Schumaker <Anna.Schumaker@Netapp.com>
Cc: Chao Yu <chao@kernel.org>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Fam Zheng <fam.zheng@bytedance.com>
Cc: Jaegeuk Kim <jaegeuk@kernel.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Kari Argillander <kari.argillander@gmail.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Qi Zheng <zhengqi.arch@bytedance.com>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: Theodore Ts'o <tytso@mit.edu>
Cc: Trond Myklebust <trond.myklebust@hammerspace.com>
Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Wei Yang <richard.weiyang@gmail.com>
Cc: Xiongchun Duan <duanxiongchun@bytedance.com>
Cc: Yang Shi <shy828301@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Documentation/filesystems/porting.rst

@@ -45,6 +45,12 @@ 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 to set up the inode reclaim context
+correctly.
+
 ---
 
 **mandatory**

fs/inode.c

@@ -259,7 +259,7 @@ 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;

include/linux/fs.h

@@ -42,6 +42,7 @@
 #include <linux/mount.h>
 #include <linux/cred.h>
 #include <linux/mnt_idmapping.h>
+#include <linux/slab.h>
 
 #include <asm/byteorder.h>
 #include <uapi/linux/fs.h>
@@ -3114,6 +3115,16 @@ 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)
 {