On Fri, 13 Jul 2007 18:36:54 -0700 Badari Pulavarty <pbadari@xxxxxxxxxx> wrote: > More statfs() improvements for ext2. ext2 already maintains > percpu counters for free blocks and inodes. Derive free > block count and inode count by summing up percpu counters, > instead of counting up all the groups in the filesystem > each time. > hm, another speedup patch with no measurements which demonstrate its benefit. > > Signed-off-by: Badari Pulavarty <pbadari@xxxxxxxxxx> > Acked-by: Andreas Dilger <adilger@xxxxxxxxxxxxx> > > fs/ext2/super.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > Index: linux-2.6.22/fs/ext2/super.c > =================================================================== > --- linux-2.6.22.orig/fs/ext2/super.c 2007-07-13 20:06:38.000000000 -0700 > +++ linux-2.6.22/fs/ext2/super.c 2007-07-13 20:06:51.000000000 -0700 > @@ -1136,12 +1136,12 @@ static int ext2_statfs (struct dentry * > buf->f_type = EXT2_SUPER_MAGIC; > buf->f_bsize = sb->s_blocksize; > buf->f_blocks = le32_to_cpu(es->s_blocks_count) - overhead; > - buf->f_bfree = ext2_count_free_blocks(sb); > + buf->f_bfree = percpu_counter_sum(&sbi->s_freeblocks_counter); > buf->f_bavail = buf->f_bfree - le32_to_cpu(es->s_r_blocks_count); > if (buf->f_bfree < le32_to_cpu(es->s_r_blocks_count)) > buf->f_bavail = 0; > buf->f_files = le32_to_cpu(es->s_inodes_count); > - buf->f_ffree = ext2_count_free_inodes(sb); > + buf->f_ffree = percpu_counter_sum(&sbi->s_freeinodes_counter); > buf->f_namelen = EXT2_NAME_LEN; > fsid = le64_to_cpup((void *)es->s_uuid) ^ > le64_to_cpup((void *)es->s_uuid + sizeof(u64)); > Well there's a tradeoff here. At large CPU counts, percpu_counter_sum() becomes quite expensive - it takes a global lock and then goes off fishing in every CPU's percpu_alloced memory. So there is some value of (num_online_cpus / sb->s_groups_count) at which this change becomes a loss. Where does that value lie? Bear in mind that the global lock in percpu_counter_sum() will tilt the scales quite a bit. - To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
