ext4: make ext4_block_in_group() much more efficient
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>
diff --git a/fs/ext4/balloc.c b/fs/ext4/balloc.c
index 92e68b3..d6babf9 100644
--- a/fs/ext4/balloc.c
+++ b/fs/ext4/balloc.c
@@ -49,14 +49,24 @@
}
-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