| Message ID | 1364207051-27037-1-git-send-email-lczerner@redhat.com |
|---|---|
| State | Superseded, archived |
| Headers | show |
On Mon, Mar 25, 2013 at 11:24:10AM +0100, Lukas Czerner wrote: > + actual_group = (le32_to_cpu(EXT4_SB(sb)->s_es->s_first_data_block) + > + block) >> > + (EXT4_BLOCK_SIZE_BITS(sb) + EXT4_CLUSTER_BITS(sb) + 3); The problem with this change is that you are assuming that the number of blocks per group is equal to block_size * 8. This is not always the case; a nonstandard number of blocks per group can be set using mke2fs's -g option. - Ted -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/fs/ext4/balloc.c b/fs/ext4/balloc.c index 92e68b3..68368c2 100644 --- a/fs/ext4/balloc.c +++ b/fs/ext4/balloc.c @@ -49,14 +49,19 @@ void ext4_get_group_no_and_offset(struct super_block *sb, ext4_fsblk_t blocknr, } -static int ext4_block_in_group(struct super_block *sb, ext4_fsblk_t block, - ext4_group_t block_group) +/* + * Check whether the 'block' lives within the 'block_group'. Returns 1 if so + * and 0 otherwise. + */ +static inline int ext4_block_in_group(struct super_block *sb, + ext4_fsblk_t block, + ext4_group_t block_group) { ext4_group_t actual_group; - ext4_get_group_no_and_offset(sb, block, &actual_group, NULL); - if (actual_group == block_group) - return 1; - return 0; + actual_group = (le32_to_cpu(EXT4_SB(sb)->s_es->s_first_data_block) + + block) >> + (EXT4_BLOCK_SIZE_BITS(sb) + EXT4_CLUSTER_BITS(sb) + 3); + return (actual_group == block_group) ? 1 : 0; } /* Return the number of clusters used for file system metadata; this
Currently in when getting the block group number for a particular block in ext4_block_in_group() we're using ext4_get_group_no_and_offset() which uses do_div() to get the block group and the remainer which is offset within the group. We don't need all of that in ext4_block_in_group() as we only need to figure out the group number. This commit changes ext4_block_in_group() to calculate group number directly. This shows as a big improvement with regards to cpu utilization. Measuring fallocate -l 15T on fresh file system with perf showed that 23% of cpu time was spend in the ext4_get_group_no_and_offset(). With this change it completely disappears from the list only bumping the occurrence of ext4_init_block_bitmap() which is the biggest user of ext4_block_in_group() by 4%. As the result of this change on my system the fallocate call was approx. 10% faster. Signed-off-by: Lukas Czerner <lczerner@redhat.com> --- fs/ext4/balloc.c | 17 +++++++++++------ 1 files changed, 11 insertions(+), 6 deletions(-)