nilfs2: eliminate the shared counter and spinlock for i_generation

Use get_random_u32() as the source for inode->i_generation for new inodes,
and eliminate the original source, the shared counter ns_next_generation
along with its exclusive access spinlock ns_next_gen_lock.

Link: https://lkml.kernel.org/r/20240826174116.5008-5-konishi.ryusuke@gmail.comSigned-off-by: Ryusuke Konishi <konishi.ryusuke@gmail.com>
Cc: Huang Xiaojia <huangxiaojia2@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

fs/nilfs2/inode.c

@@ -15,6 +15,7 @@
 #include <linux/writeback.h>
 #include <linux/uio.h>
 #include <linux/fiemap.h>
+#include <linux/random.h>
 #include "nilfs.h"
 #include "btnode.h"
 #include "segment.h"
@@ -320,7 +321,6 @@ static int nilfs_insert_inode_locked(struct inode *inode,
 struct inode *nilfs_new_inode(struct inode *dir, umode_t mode)
 {
 	struct super_block *sb = dir->i_sb;
-	struct the_nilfs *nilfs = sb->s_fs_info;
 	struct inode *inode;
 	struct nilfs_inode_info *ii;
 	struct nilfs_root *root;
@@ -381,9 +381,7 @@ struct inode *nilfs_new_inode(struct inode *dir, umode_t mode)
 	/* ii->i_dir_acl = 0; */
 	ii->i_dir_start_lookup = 0;
 	nilfs_set_inode_flags(inode);
-	spin_lock(&nilfs->ns_next_gen_lock);
-	inode->i_generation = nilfs->ns_next_generation++;
-	spin_unlock(&nilfs->ns_next_gen_lock);
+	inode->i_generation = get_random_u32();
 	if (nilfs_insert_inode_locked(inode, root, ino) < 0) {
 		err = -EIO;
 		goto failed_after_creation;

fs/nilfs2/the_nilfs.c

@@ -12,7 +12,6 @@
 #include <linux/slab.h>
 #include <linux/blkdev.h>
 #include <linux/backing-dev.h>
-#include <linux/random.h>
 #include <linux/log2.h>
 #include <linux/crc32.h>
 #include "nilfs.h"
@@ -69,7 +68,6 @@ struct the_nilfs *alloc_nilfs(struct super_block *sb)
 	INIT_LIST_HEAD(&nilfs->ns_dirty_files);
 	INIT_LIST_HEAD(&nilfs->ns_gc_inodes);
 	spin_lock_init(&nilfs->ns_inode_lock);
-	spin_lock_init(&nilfs->ns_next_gen_lock);
 	spin_lock_init(&nilfs->ns_last_segment_lock);
 	nilfs->ns_cptree = RB_ROOT;
 	spin_lock_init(&nilfs->ns_cptree_lock);
@@ -754,9 +752,6 @@ int init_nilfs(struct the_nilfs *nilfs, struct super_block *sb)
 	nilfs->ns_blocksize_bits = sb->s_blocksize_bits;
 	nilfs->ns_blocksize = blocksize;
 
-	get_random_bytes(&nilfs->ns_next_generation,
-			 sizeof(nilfs->ns_next_generation));
-
 	err = nilfs_store_disk_layout(nilfs, sbp);
 	if (err)
 		goto failed_sbh;

fs/nilfs2/the_nilfs.h

@@ -71,8 +71,6 @@ enum {
  * @ns_dirty_files: list of dirty files
  * @ns_inode_lock: lock protecting @ns_dirty_files
  * @ns_gc_inodes: dummy inodes to keep live blocks
- * @ns_next_generation: next generation number for inodes
- * @ns_next_gen_lock: lock protecting @ns_next_generation
  * @ns_mount_opt: mount options
  * @ns_resuid: uid for reserved blocks
  * @ns_resgid: gid for reserved blocks
@@ -161,10 +159,6 @@ struct the_nilfs {
 	/* GC inode list */
 	struct list_head	ns_gc_inodes;
 
-	/* Inode allocator */
-	u32			ns_next_generation;
-	spinlock_t		ns_next_gen_lock;
-
 	/* Mount options */
 	unsigned long		ns_mount_opt;