xiaomi-sm8450/android_kernel_xiaomi_sm8450
1
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

ext4: make ext4_block_in_group() much more efficient

Browse Source 
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.

However since there is '-g' option in mkfs which allow us setting
different groups size (mostly for developers) I've introduced new per
file system flag whether we have a standard block group size or
not. The flag is used to determine whether we can use the bit shift
optimization or not.

Signed-off-by: Lukas Czerner <lczerner@redhat.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
This commit is contained in:
Lukas Czerner
2013-04-03 22:12:52 -04:00
committed by Theodore Ts'o
parent a75ae78f08
commit 689110098c
3 changed files with 29 additions and 7 deletions
Download Patch File Download Diff File Expand all files Collapse all files

22
fs/ext4/balloc.c
View File

@@ -49,14 +49,24 @@ 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;
if (test_opt2(sb, STD_GROUP_SIZE))
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);
else
ext4_get_group_no_and_offset(sb, block, &actual_group, NULL);
return (actual_group == block_group) ? 1 : 0;
}
/* Return the number of clusters used for file system metadata; this