[RFC PATCH v3 1/2] tmpfs: manage the inode-number by IDR, signed int inum

["J. R. Okajima" <hooanon05g@gmail.com>]

To ensure the uniquness of the inode-number, manage it by IDR.
Also it tries using the lowest unused inode-number, so the value will
usually be smaller.
Another side effect is the type of the inode-number in tmpfs. By using
IDR, it is limited to signed int. But I don't think it a big
problem. INT_MAX is big enough for the number of inodes in a single tmpfs.

Cc: Eric Dumazet <edumazet@google.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Andreas Dilger <adilger@dilger.ca>
Cc: Jan Kara <jack@suse.cz>
Signed-off-by: J. R. Okajima <hooanon05g@gmail.com>
---
 include/linux/shmem_fs.h |    6 ++++--
 mm/shmem.c               |   37 +++++++++++++++++++++++++++++++------
 2 files changed, 35 insertions(+), 8 deletions(-)

diff --git a/include/linux/shmem_fs.h b/include/linux/shmem_fs.h
index 4d1771c..4ba8b43 100644
--- a/include/linux/shmem_fs.h
+++ b/include/linux/shmem_fs.h
@@ -24,10 +24,12 @@ struct shmem_inode_info {
 };
 
 struct shmem_sb_info {
+	struct mutex idr_lock;
+	struct idr idr;		    /* manages inode-number */
 	unsigned long max_blocks;   /* How many blocks are allowed */
 	struct percpu_counter used_blocks;  /* How many are allocated */
-	unsigned long max_inodes;   /* How many inodes are allowed */
-	unsigned long free_inodes;  /* How many are left for allocation */
+	int max_inodes;		    /* How many inodes are allowed */
+	int free_inodes;	    /* How many are left for allocation */
 	spinlock_t stat_lock;	    /* Serialize shmem_sb_info changes */
 	kuid_t uid;		    /* Mount uid for root directory */
 	kgid_t gid;		    /* Mount gid for root directory */
diff --git a/mm/shmem.c b/mm/shmem.c
index 368f314..0023d8d 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -107,9 +107,13 @@ static unsigned long shmem_default_max_blocks(void)
 	return totalram_pages / 2;
 }
 
-static unsigned long shmem_default_max_inodes(void)
+static int shmem_default_max_inodes(void)
 {
-	return min(totalram_pages - totalhigh_pages, totalram_pages / 2);
+	int i;
+
+	i = min(totalram_pages - totalhigh_pages, totalram_pages / 2);
+	i = min(i, INT_MAX);
+	return i;
 }
 #endif
 
@@ -569,6 +573,7 @@ static int shmem_setattr(struct dentry *dentry, struct iattr *attr)
 static void shmem_evict_inode(struct inode *inode)
 {
 	struct shmem_inode_info *info = SHMEM_I(inode);
+	struct shmem_sb_info *sbinfo = SHMEM_SB(inode->i_sb);
 
 	if (inode->i_mapping->a_ops == &shmem_aops) {
 		shmem_unacct_size(info->flags, inode->i_size);
@@ -584,6 +589,11 @@ static void shmem_evict_inode(struct inode *inode)
 
 	simple_xattrs_free(&info->xattrs);
 	WARN_ON(inode->i_blocks);
+	if (inode->i_ino) {
+		mutex_lock(&sbinfo->idr_lock);
+		idr_remove(&sbinfo->idr, inode->i_ino);
+		mutex_unlock(&sbinfo->idr_lock);
+	}
 	shmem_free_inode(inode->i_sb);
 	clear_inode(inode);
 }
@@ -1315,13 +1325,13 @@ static struct inode *shmem_get_inode(struct super_block *sb, const struct inode
 	struct inode *inode;
 	struct shmem_inode_info *info;
 	struct shmem_sb_info *sbinfo = SHMEM_SB(sb);
+	int ino;
 
 	if (shmem_reserve_inode(sb))
 		return NULL;
 
 	inode = new_inode(sb);
 	if (inode) {
-		inode->i_ino = get_next_ino();
 		inode_init_owner(inode, dir, mode);
 		inode->i_blocks = 0;
 		inode->i_mapping->backing_dev_info = &shmem_backing_dev_info;
@@ -1362,6 +1372,18 @@ static struct inode *shmem_get_inode(struct super_block *sb, const struct inode
 			mpol_shared_policy_init(&info->policy, NULL);
 			break;
 		}
+
+		/* inum 0 and 1 are unused */
+		mutex_lock(&sbinfo->idr_lock);
+		ino = idr_alloc(&sbinfo->idr, inode, 2, INT_MAX, GFP_NOFS);
+		if (ino > 0) {
+			inode->i_ino = ino;
+			mutex_unlock(&sbinfo->idr_lock);
+		} else {
+			mutex_unlock(&sbinfo->idr_lock);
+			iput(inode);	/* shmem_free_inode() will be called */
+			inode = NULL;
+		}
 	} else
 		shmem_free_inode(sb);
 	return inode;
@@ -2385,7 +2407,7 @@ static int shmem_parse_options(char *options, struct shmem_sb_info *sbinfo,
 				goto bad_val;
 		} else if (!strcmp(this_char,"nr_inodes")) {
 			sbinfo->max_inodes = memparse(value, &rest);
-			if (*rest)
+			if (*rest || sbinfo->max_inodes < 2)
 				goto bad_val;
 		} else if (!strcmp(this_char,"mode")) {
 			if (remount)
@@ -2438,7 +2460,7 @@ static int shmem_remount_fs(struct super_block *sb, int *flags, char *data)
 {
 	struct shmem_sb_info *sbinfo = SHMEM_SB(sb);
 	struct shmem_sb_info config = *sbinfo;
-	unsigned long inodes;
+	int inodes;
 	int error = -EINVAL;
 
 	config.mpol = NULL;
@@ -2486,7 +2508,7 @@ static int shmem_show_options(struct seq_file *seq, struct dentry *root)
 		seq_printf(seq, ",size=%luk",
 			sbinfo->max_blocks << (PAGE_CACHE_SHIFT - 10));
 	if (sbinfo->max_inodes != shmem_default_max_inodes())
-		seq_printf(seq, ",nr_inodes=%lu", sbinfo->max_inodes);
+		seq_printf(seq, ",nr_inodes=%d", sbinfo->max_inodes);
 	if (sbinfo->mode != (S_IRWXUGO | S_ISVTX))
 		seq_printf(seq, ",mode=%03ho", sbinfo->mode);
 	if (!uid_eq(sbinfo->uid, GLOBAL_ROOT_UID))
@@ -2504,6 +2526,7 @@ static void shmem_put_super(struct super_block *sb)
 {
 	struct shmem_sb_info *sbinfo = SHMEM_SB(sb);
 
+	idr_destroy(&sbinfo->idr);
 	percpu_counter_destroy(&sbinfo->used_blocks);
 	mpol_put(sbinfo->mpol);
 	kfree(sbinfo);
@@ -2522,6 +2545,8 @@ int shmem_fill_super(struct super_block *sb, void *data, int silent)
 	if (!sbinfo)
 		return -ENOMEM;
 
+	mutex_init(&sbinfo->idr_lock);
+	idr_init(&sbinfo->idr);
 	sbinfo->mode = S_IRWXUGO | S_ISVTX;
 	sbinfo->uid = current_fsuid();
 	sbinfo->gid = current_fsgid();
-- 
1.7.10.4