tmpfs: track free_ispace instead of free_inodes

In preparation for assigning some inode space to extended attributes,
keep track of free_ispace instead of number of free_inodes: as if one
tmpfs inode (and accompanying dentry) occupies very approximately 1KiB.

Unsigned long is large enough for free_ispace, on 64-bit and on 32-bit:
but take care to enforce the maximum.  And fix the nr_blocks maximum on
32-bit: S64_MAX would be too big for it there, so say LONG_MAX instead.

Delete the incorrect limited<->unlimited blocks/inodes comment above
shmem_reconfigure(): leave it to the error messages below to describe.

Signed-off-by: Hugh Dickins <hughd@google.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Carlos Maiolino <cmaiolino@redhat.com>
Message-Id: <4fe1739-d9e7-8dfd-5bce-12e7339711da@google.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>

diff --git a/include/linux/shmem_fs.h b/include/linux/shmem_fs.h
index 9b2d2fa..6b0c626 100644 (file)
--- a/include/linux/shmem_fs.h
+++ b/include/linux/shmem_fs.h
@@ -54,7 +54,7 @@ struct shmem_sb_info {
        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 */
+       unsigned long free_ispace;  /* How much ispace left for allocation */
        raw_spinlock_t stat_lock;   /* Serialize shmem_sb_info changes */
        umode_t mode;               /* Mount mode for root directory */
        unsigned char huge;         /* Whether to try for hugepages */

diff --git a/mm/shmem.c b/mm/shmem.c
index b22d0bf..8c8f0b1 100644 (file)
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -90,6 +90,9 @@ static struct vfsmount *shm_mnt;
 /* Pretend that each entry is of this size in directory's i_size */
 #define BOGO_DIRENT_SIZE 20
 
+/* Pretend that one inode + its dentry occupy this much memory */
+#define BOGO_INODE_SIZE 1024
+
 /* Symlink up to this size is kmalloc'ed instead of using a swappable page */
 #define SHORT_SYMLINK_LEN 128
 
@@ -137,7 +140,8 @@ static unsigned long shmem_default_max_inodes(void)
 {
        unsigned long nr_pages = totalram_pages();
 
-       return min(nr_pages - totalhigh_pages(), nr_pages / 2);
+       return min3(nr_pages - totalhigh_pages(), nr_pages / 2,
+                       ULONG_MAX / BOGO_INODE_SIZE);
 }
 #endif
 
@@ -331,11 +335,11 @@ static int shmem_reserve_inode(struct super_block *sb, ino_t *inop)
        if (!(sb->s_flags & SB_KERNMOUNT)) {
                raw_spin_lock(&sbinfo->stat_lock);
                if (sbinfo->max_inodes) {
-                       if (!sbinfo->free_inodes) {
+                       if (sbinfo->free_ispace < BOGO_INODE_SIZE) {
                                raw_spin_unlock(&sbinfo->stat_lock);
                                return -ENOSPC;
                        }
-                       sbinfo->free_inodes--;
+                       sbinfo->free_ispace -= BOGO_INODE_SIZE;
                }
                if (inop) {
                        ino = sbinfo->next_ino++;
@@ -394,7 +398,7 @@ static void shmem_free_inode(struct super_block *sb)
        struct shmem_sb_info *sbinfo = SHMEM_SB(sb);
        if (sbinfo->max_inodes) {
                raw_spin_lock(&sbinfo->stat_lock);
-               sbinfo->free_inodes++;
+               sbinfo->free_ispace += BOGO_INODE_SIZE;
                raw_spin_unlock(&sbinfo->stat_lock);
        }
 }
@@ -3158,7 +3162,7 @@ static int shmem_statfs(struct dentry *dentry, struct kstatfs *buf)
        }
        if (sbinfo->max_inodes) {
                buf->f_files = sbinfo->max_inodes;
-               buf->f_ffree = sbinfo->free_inodes;
+               buf->f_ffree = sbinfo->free_ispace / BOGO_INODE_SIZE;
        }
        /* else leave those fields 0 like simple_statfs */
 
@@ -3818,13 +3822,13 @@ static int shmem_parse_one(struct fs_context *fc, struct fs_parameter *param)
                break;
        case Opt_nr_blocks:
                ctx->blocks = memparse(param->string, &rest);
-               if (*rest || ctx->blocks > S64_MAX)
+               if (*rest || ctx->blocks > LONG_MAX)
                        goto bad_value;
                ctx->seen |= SHMEM_SEEN_BLOCKS;
                break;
        case Opt_nr_inodes:
                ctx->inodes = memparse(param->string, &rest);
-               if (*rest)
+               if (*rest || ctx->inodes > ULONG_MAX / BOGO_INODE_SIZE)
                        goto bad_value;
                ctx->seen |= SHMEM_SEEN_INODES;
                break;
@@ -4005,21 +4009,17 @@ static int shmem_parse_options(struct fs_context *fc, void *data)
 
 /*
  * Reconfigure a shmem filesystem.
- *
- * Note that we disallow change from limited->unlimited blocks/inodes while any
- * are in use; but we must separately disallow unlimited->limited, because in
- * that case we have no record of how much is already in use.
  */
 static int shmem_reconfigure(struct fs_context *fc)
 {
        struct shmem_options *ctx = fc->fs_private;
        struct shmem_sb_info *sbinfo = SHMEM_SB(fc->root->d_sb);
-       unsigned long inodes;
+       unsigned long used_isp;
        struct mempolicy *mpol = NULL;
        const char *err;
 
        raw_spin_lock(&sbinfo->stat_lock);
-       inodes = sbinfo->max_inodes - sbinfo->free_inodes;
+       used_isp = sbinfo->max_inodes * BOGO_INODE_SIZE - sbinfo->free_ispace;
 
        if ((ctx->seen & SHMEM_SEEN_BLOCKS) && ctx->blocks) {
                if (!sbinfo->max_blocks) {
@@ -4037,7 +4037,7 @@ static int shmem_reconfigure(struct fs_context *fc)
                        err = "Cannot retroactively limit inodes";
                        goto out;
                }
-               if (ctx->inodes < inodes) {
+               if (ctx->inodes * BOGO_INODE_SIZE < used_isp) {
                        err = "Too few inodes for current use";
                        goto out;
                }
@@ -4083,7 +4083,7 @@ static int shmem_reconfigure(struct fs_context *fc)
                sbinfo->max_blocks  = ctx->blocks;
        if (ctx->seen & SHMEM_SEEN_INODES) {
                sbinfo->max_inodes  = ctx->inodes;
-               sbinfo->free_inodes = ctx->inodes - inodes;
+               sbinfo->free_ispace = ctx->inodes * BOGO_INODE_SIZE - used_isp;
        }
 
        /*
@@ -4214,7 +4214,8 @@ static int shmem_fill_super(struct super_block *sb, struct fs_context *fc)
        sb->s_flags |= SB_NOUSER;
 #endif
        sbinfo->max_blocks = ctx->blocks;
-       sbinfo->free_inodes = sbinfo->max_inodes = ctx->inodes;
+       sbinfo->max_inodes = ctx->inodes;
+       sbinfo->free_ispace = sbinfo->max_inodes * BOGO_INODE_SIZE;
        if (sb->s_flags & SB_KERNMOUNT) {
                sbinfo->ino_batch = alloc_percpu(ino_t);
                if (!sbinfo->ino_batch)