ext4: statfs speed up

This is a patch that speeds up statfs.  It is very simple - the "overhead"
calculation, which takes a huge amount of time for large filesystems, never
changes unless the size of the filesystem itself changes.  That means we can
store it in memory and only recalculate if the filesystem has been resized
(almost never).

It also fixes a minor problem that we never update the on-disk superblock free
blocks/inodes counts until the filesystem is unmounted.  While not fatal, we
may as well update that on disk when we have the information, and it makes
things like debugfs and dumpe2fs report a bit more accurate info.

Signed-off-by: Badari Pulavarty <pbadari@us.ibm.com>
Signed-off-by: Andreas Dilger <adilger@clusterfs.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 15 insertions, 10 deletions

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index adcbfadfcb4c..d0d8c76c7edb 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -2500,19 +2500,19 @@ static int ext4_statfs (struct dentry * dentry, struct kstatfs * buf)
         struct super_block *sb = dentry->d_sb;
         struct ext4_sb_info *sbi = EXT4_SB(sb);
         struct ext4_super_block *es = sbi->s_es;
-        ext4_fsblk_t overhead;
-        int i;
         u64 fsid;
 
-        if (test_opt (sb, MINIX_DF))
-                overhead = 0;
-        else {
-                unsigned long ngroups;
-                ngroups = EXT4_SB(sb)->s_groups_count;
+        if (test_opt(sb, MINIX_DF)) {
+                sbi->s_overhead_last = 0;
+        } else if (sbi->s_blocks_last != le32_to_cpu(es->s_blocks_count)) {
+                unsigned long ngroups = sbi->s_groups_count, i;
+                ext4_fsblk_t overhead = 0;
                 smp_rmb();
 
                 /*
-                 * Compute the overhead (FS structures)
+                 * Compute the overhead (FS structures).  This is constant
+                 * for a given filesystem unless the number of block groups
+                 * changes so we cache the previous value until it does.
                  */
 
                 /*
@@ -2536,18 +2536,23 @@ static int ext4_statfs (struct dentry * dentry, struct kstatfs * buf)
                  * Every block group has an inode bitmap, a block
                  * bitmap, and an inode table.
                  */
-                overhead += (ngroups * (2 + EXT4_SB(sb)->s_itb_per_group));
+                overhead += ngroups * (2 + sbi->s_itb_per_group);
+                sbi->s_overhead_last = overhead;
+                smp_wmb();
+                sbi->s_blocks_last = le32_to_cpu(es->s_blocks_count);
         }
 
         buf->f_type = EXT4_SUPER_MAGIC;
         buf->f_bsize = sb->s_blocksize;
-        buf->f_blocks = ext4_blocks_count(es) - overhead;
+        buf->f_blocks = ext4_blocks_count(es) - sbi->s_overhead_last;
         buf->f_bfree = percpu_counter_sum(&sbi->s_freeblocks_counter);
+        es->s_free_blocks_count = cpu_to_le32(buf->f_bfree);
         buf->f_bavail = buf->f_bfree - ext4_r_blocks_count(es);
         if (buf->f_bfree < ext4_r_blocks_count(es))
                 buf->f_bavail = 0;
         buf->f_files = le32_to_cpu(es->s_inodes_count);
         buf->f_ffree = percpu_counter_sum(&sbi->s_freeinodes_counter);
+        es->s_free_inodes_count = cpu_to_le32(buf->f_ffree);
         buf->f_namelen = EXT4_NAME_LEN;
         fsid = le64_to_cpup((void *)es->s_uuid) ^
                le64_to_cpup((void *)es->s_uuid + sizeof(u64));