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ext4: get ext4_group_desc in ext4_mb_prefetch only when necessary

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Getting ext4_group_desc structure can contribute to the cost of
ext4_mb_prefetch() without any need, as most groups fail the
!EXT4_MB_GRP_TEST_AND_SET_READ check.

Optimize ext4_mb_prefetch by getting the group description only when
necessary.

The result is further increase in performance of fallocate() system call
path that triggers ext4_mb_prefetch() via a linear group scan.

Signed-off-by: Bohdan Trach <bohdan.trach@huaweicloud.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Andreas Dilger <adilger@dilger.ca>
Link: https://patch.msgid.link/20260615100331.163997-3-bohdan.trach@huaweicloud.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
This commit is contained in:
Bohdan Trach 2026-06-15 12:03:29 +02:00 committed by Theodore Ts'o
parent 0e364a0302
commit a6a1e7e569
1 changed files with 11 additions and 10 deletions
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21
fs/ext4/mballoc.c
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@ -2861,8 +2861,6 @@ ext4_group_t ext4_mb_prefetch(struct super_block *sb, ext4_group_t group,
blk_start_plug(&plug);
while (nr-- > 0) {
struct ext4_group_desc *gdp = ext4_get_group_desc(sb, group,
NULL);
struct ext4_group_info *grp = ext4_get_group_info(sb, group);
/*
@ -2872,14 +2870,17 @@ ext4_group_t ext4_mb_prefetch(struct super_block *sb, ext4_group_t group,
* prefetch once, so we avoid getblk() call, which can
* be expensive.
*/
if (gdp && grp && !EXT4_MB_GRP_TEST_AND_SET_READ(grp) &&
EXT4_MB_GRP_NEED_INIT(grp) &&
ext4_free_group_clusters(sb, gdp) > 0 ) {
bh = ext4_read_block_bitmap_nowait(sb, group, true);
if (!IS_ERR_OR_NULL(bh)) {
if (!buffer_uptodate(bh) && cnt)
(*cnt)++;
brelse(bh);
if (grp && !EXT4_MB_GRP_TEST_AND_SET_READ(grp) &&
EXT4_MB_GRP_NEED_INIT(grp)) {
struct ext4_group_desc *gdp = ext4_get_group_desc(sb, group, NULL);
if (gdp && ext4_free_group_clusters(sb, gdp) > 0) {
bh = ext4_read_block_bitmap_nowait(sb, group, true);
if (!IS_ERR_OR_NULL(bh)) {
if (!buffer_uptodate(bh) && cnt)
(*cnt)++;
brelse(bh);
}
}
}
if (++group >= ngroups)