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ext4: factor out ext4_mb_might_prefetch()

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Extract ext4_mb_might_prefetch() to make the code clearer and to
prepare for the later conversion of 'choose group' to 'scan groups'.
No functional changes.

Signed-off-by: Baokun Li <libaokun1@huawei.com>
Reviewed-by: Zhang Yi <yi.zhang@huawei.com>
Link: https://patch.msgid.link/20250714130327.1830534-14-libaokun1@huawei.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
This commit is contained in:
Baokun Li
2025-07-14 21:03:23 +08:00
committed by Theodore Ts'o
parent 45704f92e5
commit 5abd85f667
2 changed files with 42 additions and 24 deletions
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62
fs/ext4/mballoc.c
View File

@@ -2781,6 +2781,37 @@ ext4_group_t ext4_mb_prefetch(struct super_block *sb, ext4_group_t group,
return group;
}
/*
* Batch reads of the block allocation bitmaps to get
* multiple READs in flight; limit prefetching at inexpensive
* CR, otherwise mballoc can spend a lot of time loading
* imperfect groups
*/
static void ext4_mb_might_prefetch(struct ext4_allocation_context *ac,
ext4_group_t group)
{
struct ext4_sb_info *sbi;
if (ac->ac_prefetch_grp != group)
return;
sbi = EXT4_SB(ac->ac_sb);
if (ext4_mb_cr_expensive(ac->ac_criteria) ||
ac->ac_prefetch_ios < sbi->s_mb_prefetch_limit) {
unsigned int nr = sbi->s_mb_prefetch;
if (ext4_has_feature_flex_bg(ac->ac_sb)) {
nr = 1 << sbi->s_log_groups_per_flex;
nr -= group & (nr - 1);
nr = umin(nr, sbi->s_mb_prefetch);
}
ac->ac_prefetch_nr = nr;
ac->ac_prefetch_grp = ext4_mb_prefetch(ac->ac_sb, group, nr,
&ac->ac_prefetch_ios);
}
}
/*
* Prefetching reads the block bitmap into the buffer cache; but we
* need to make sure that the buddy bitmap in the page cache has been
@@ -2817,10 +2848,9 @@ void ext4_mb_prefetch_fini(struct super_block *sb, ext4_group_t group,
static noinline_for_stack int
ext4_mb_regular_allocator(struct ext4_allocation_context *ac)
{
ext4_group_t prefetch_grp = 0, ngroups, group, i;
ext4_group_t ngroups, group, i;
enum criteria new_cr, cr = CR_GOAL_LEN_FAST;
int err = 0, first_err = 0;
unsigned int nr = 0, prefetch_ios = 0;
struct ext4_sb_info *sbi;
struct super_block *sb;
struct ext4_buddy e4b;
@@ -2881,6 +2911,7 @@ ext4_mb_regular_allocator(struct ext4_allocation_context *ac)
cr = CR_POWER2_ALIGNED;
ac->ac_e4b = &e4b;
ac->ac_prefetch_ios = 0;
repeat:
for (; cr < EXT4_MB_NUM_CRS && ac->ac_status == AC_STATUS_CONTINUE; cr++) {
ac->ac_criteria = cr;
@@ -2890,8 +2921,8 @@ ext4_mb_regular_allocator(struct ext4_allocation_context *ac)
*/
group = ac->ac_g_ex.fe_group;
ac->ac_groups_linear_remaining = sbi->s_mb_max_linear_groups;
prefetch_grp = group;
nr = 0;
ac->ac_prefetch_grp = group;
ac->ac_prefetch_nr = 0;
for (i = 0, new_cr = cr; i < ngroups; i++,
ext4_mb_choose_next_group(ac, &new_cr, &group, ngroups)) {
@@ -2903,24 +2934,7 @@ ext4_mb_regular_allocator(struct ext4_allocation_context *ac)
goto repeat;
}
/*
* Batch reads of the block allocation bitmaps
* to get multiple READs in flight; limit
* prefetching at inexpensive CR, otherwise mballoc
* can spend a lot of time loading imperfect groups
*/
if ((prefetch_grp == group) &&
(ext4_mb_cr_expensive(cr) ||
prefetch_ios < sbi->s_mb_prefetch_limit)) {
nr = sbi->s_mb_prefetch;
if (ext4_has_feature_flex_bg(sb)) {
nr = 1 << sbi->s_log_groups_per_flex;
nr -= group & (nr - 1);
nr = min(nr, sbi->s_mb_prefetch);
}
prefetch_grp = ext4_mb_prefetch(sb, group,
nr, &prefetch_ios);
}
ext4_mb_might_prefetch(ac, group);
/* prevent unnecessary buddy loading. */
if (cr < CR_ANY_FREE &&
@@ -3018,8 +3032,8 @@ ext4_mb_regular_allocator(struct ext4_allocation_context *ac)
ac->ac_b_ex.fe_len, ac->ac_o_ex.fe_len, ac->ac_status,
ac->ac_flags, cr, err);
if (nr)
ext4_mb_prefetch_fini(sb, prefetch_grp, nr);
if (ac->ac_prefetch_nr)
ext4_mb_prefetch_fini(sb, ac->ac_prefetch_grp, ac->ac_prefetch_nr);
return err;
}

4
fs/ext4/mballoc.h
View File

@@ -192,6 +192,10 @@ struct ext4_allocation_context {
*/
ext4_grpblk_t ac_orig_goal_len;
ext4_group_t ac_prefetch_grp;
unsigned int ac_prefetch_ios;
unsigned int ac_prefetch_nr;
__u32 ac_flags; /* allocation hints */
__u32 ac_groups_linear_remaining;
__u16 ac_groups_scanned;