In ext4_mb_regular_allocator(), after the call to ext4_mb_find_by_goal()
fails to achieve the inode goal, allocation continues with the stream
allocation global goal. Currently, hits for both are combined in
sbi->s_bal_goals, hindering accurate optimization.
This commit separates global goal hits into sbi->s_bal_stream_goals. Since
stream allocation doesn't use ac->ac_g_ex.fe_start, set fe_start to -1.
This prevents stream allocations from being counted in s_bal_goals. Also
clear EXT4_MB_HINT_TRY_GOAL to avoid calling ext4_mb_find_by_goal again.
After adding `stream_goal_hits`, `/proc/fs/ext4/sdx/mb_stats` will show:
mballoc:
reqs: 840347
success: 750992
groups_scanned: 1230506
cr_p2_aligned_stats:
hits: 21531
groups_considered: 411664
extents_scanned: 21531
useless_loops: 0
bad_suggestions: 6
cr_goal_fast_stats:
hits: 111222
groups_considered: 1806728
extents_scanned: 467908
useless_loops: 0
bad_suggestions: 13
cr_best_avail_stats:
hits: 36267
groups_considered: 1817631
extents_scanned: 156143
useless_loops: 0
bad_suggestions: 204
cr_goal_slow_stats:
hits: 106396
groups_considered: 5671710
extents_scanned: 22540056
useless_loops: 123747
cr_any_free_stats:
hits: 138071
groups_considered: 724692
extents_scanned: 23615593
useless_loops: 585
extents_scanned: 46804261
goal_hits: 1307
stream_goal_hits: 236317
len_goal_hits: 155549
2^n_hits: 21531
breaks: 225096
lost: 35062
buddies_generated: 40/40
buddies_time_used: 48004
preallocated: 5962467
discarded: 4847560
Signed-off-by: Baokun Li <libaokun1@huawei.com>
---
fs/ext4/ext4.h | 1 +
fs/ext4/mballoc.c | 11 +++++++++--
2 files changed, 10 insertions(+), 2 deletions(-)
diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 9df74123e7e6..8750ace12935 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -1646,6 +1646,7 @@ struct ext4_sb_info {
atomic_t s_bal_cX_ex_scanned[EXT4_MB_NUM_CRS]; /* total extents scanned */
atomic_t s_bal_groups_scanned; /* number of groups scanned */
atomic_t s_bal_goals; /* goal hits */
+ atomic_t s_bal_stream_goals; /* stream allocation global goal hits */
atomic_t s_bal_len_goals; /* len goal hits */
atomic_t s_bal_breaks; /* too long searches */
atomic_t s_bal_2orders; /* 2^order hits */
diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index 336d65c4f6a2..f56ac477c464 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -2849,8 +2849,9 @@ ext4_mb_regular_allocator(struct ext4_allocation_context *ac)
/* TBD: may be hot point */
spin_lock(&sbi->s_md_lock);
ac->ac_g_ex.fe_group = sbi->s_mb_last_group;
- ac->ac_g_ex.fe_start = sbi->s_mb_last_start;
spin_unlock(&sbi->s_md_lock);
+ ac->ac_g_ex.fe_start = -1;
+ ac->ac_flags &= ~EXT4_MB_HINT_TRY_GOAL;
}
/*
@@ -3000,8 +3001,12 @@ ext4_mb_regular_allocator(struct ext4_allocation_context *ac)
}
}
- if (sbi->s_mb_stats && ac->ac_status == AC_STATUS_FOUND)
+ if (sbi->s_mb_stats && ac->ac_status == AC_STATUS_FOUND) {
atomic64_inc(&sbi->s_bal_cX_hits[ac->ac_criteria]);
+ if (ac->ac_flags & EXT4_MB_STREAM_ALLOC &&
+ ac->ac_b_ex.fe_group == ac->ac_g_ex.fe_group)
+ atomic_inc(&sbi->s_bal_stream_goals);
+ }
out:
if (!err && ac->ac_status != AC_STATUS_FOUND && first_err)
err = first_err;
@@ -3194,6 +3199,8 @@ int ext4_seq_mb_stats_show(struct seq_file *seq, void *offset)
seq_printf(seq, "\textents_scanned: %u\n",
atomic_read(&sbi->s_bal_ex_scanned));
seq_printf(seq, "\t\tgoal_hits: %u\n", atomic_read(&sbi->s_bal_goals));
+ seq_printf(seq, "\t\tstream_goal_hits: %u\n",
+ atomic_read(&sbi->s_bal_stream_goals));
seq_printf(seq, "\t\tlen_goal_hits: %u\n",
atomic_read(&sbi->s_bal_len_goals));
seq_printf(seq, "\t\t2^n_hits: %u\n", atomic_read(&sbi->s_bal_2orders));
--
2.46.1On Mon, Jul 14, 2025 at 09:03:12PM +0800, Baokun Li wrote:
> In ext4_mb_regular_allocator(), after the call to ext4_mb_find_by_goal()
> fails to achieve the inode goal, allocation continues with the stream
> allocation global goal. Currently, hits for both are combined in
> sbi->s_bal_goals, hindering accurate optimization.
>
> This commit separates global goal hits into sbi->s_bal_stream_goals. Since
> stream allocation doesn't use ac->ac_g_ex.fe_start, set fe_start to -1.
> This prevents stream allocations from being counted in s_bal_goals. Also
> clear EXT4_MB_HINT_TRY_GOAL to avoid calling ext4_mb_find_by_goal again.
>
> After adding `stream_goal_hits`, `/proc/fs/ext4/sdx/mb_stats` will show:
>
> mballoc:
> reqs: 840347
> success: 750992
> groups_scanned: 1230506
> cr_p2_aligned_stats:
> hits: 21531
> groups_considered: 411664
> extents_scanned: 21531
> useless_loops: 0
> bad_suggestions: 6
> cr_goal_fast_stats:
> hits: 111222
> groups_considered: 1806728
> extents_scanned: 467908
> useless_loops: 0
> bad_suggestions: 13
> cr_best_avail_stats:
> hits: 36267
> groups_considered: 1817631
> extents_scanned: 156143
> useless_loops: 0
> bad_suggestions: 204
> cr_goal_slow_stats:
> hits: 106396
> groups_considered: 5671710
> extents_scanned: 22540056
> useless_loops: 123747
> cr_any_free_stats:
> hits: 138071
> groups_considered: 724692
> extents_scanned: 23615593
> useless_loops: 585
> extents_scanned: 46804261
> goal_hits: 1307
> stream_goal_hits: 236317
> len_goal_hits: 155549
> 2^n_hits: 21531
> breaks: 225096
> lost: 35062
> buddies_generated: 40/40
> buddies_time_used: 48004
> preallocated: 5962467
> discarded: 4847560
>
> Signed-off-by: Baokun Li <libaokun1@huawei.com>
> ---
> fs/ext4/ext4.h | 1 +
> fs/ext4/mballoc.c | 11 +++++++++--
> 2 files changed, 10 insertions(+), 2 deletions(-)
>
> diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
> index 9df74123e7e6..8750ace12935 100644
> --- a/fs/ext4/ext4.h
> +++ b/fs/ext4/ext4.h
> @@ -1646,6 +1646,7 @@ struct ext4_sb_info {
> atomic_t s_bal_cX_ex_scanned[EXT4_MB_NUM_CRS]; /* total extents scanned */
> atomic_t s_bal_groups_scanned; /* number of groups scanned */
> atomic_t s_bal_goals; /* goal hits */
> + atomic_t s_bal_stream_goals; /* stream allocation global goal hits */
> atomic_t s_bal_len_goals; /* len goal hits */
> atomic_t s_bal_breaks; /* too long searches */
> atomic_t s_bal_2orders; /* 2^order hits */
> diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
> index 336d65c4f6a2..f56ac477c464 100644
> --- a/fs/ext4/mballoc.c
> +++ b/fs/ext4/mballoc.c
> @@ -2849,8 +2849,9 @@ ext4_mb_regular_allocator(struct ext4_allocation_context *ac)
> /* TBD: may be hot point */
> spin_lock(&sbi->s_md_lock);
> ac->ac_g_ex.fe_group = sbi->s_mb_last_group;
> - ac->ac_g_ex.fe_start = sbi->s_mb_last_start;
> spin_unlock(&sbi->s_md_lock);
> + ac->ac_g_ex.fe_start = -1;
> + ac->ac_flags &= ~EXT4_MB_HINT_TRY_GOAL;
Hey Baokun, I was a bit late to review this in v2 so I'll add the
comment here:
So this is mostly to account for retires right? Maybe rather than
disabling goal allocation a better way to do this is resetting the
original goal group and goal start in the retry logic of
ext4_mb_new_blocks()? Since we drop preallocations before retrying, this
way we might actually find our goal during the retry. Its a slim chance
though but still feels like the right way to do it.
Thoughts?
Regards,
ojaswin
> }
>
> /*
> @@ -3000,8 +3001,12 @@ ext4_mb_regular_allocator(struct ext4_allocation_context *ac)
> }
> }
>
> - if (sbi->s_mb_stats && ac->ac_status == AC_STATUS_FOUND)
> + if (sbi->s_mb_stats && ac->ac_status == AC_STATUS_FOUND) {
> atomic64_inc(&sbi->s_bal_cX_hits[ac->ac_criteria]);
> + if (ac->ac_flags & EXT4_MB_STREAM_ALLOC &&
> + ac->ac_b_ex.fe_group == ac->ac_g_ex.fe_group)
> + atomic_inc(&sbi->s_bal_stream_goals);
> + }
> out:
> if (!err && ac->ac_status != AC_STATUS_FOUND && first_err)
> err = first_err;
> @@ -3194,6 +3199,8 @@ int ext4_seq_mb_stats_show(struct seq_file *seq, void *offset)
> seq_printf(seq, "\textents_scanned: %u\n",
> atomic_read(&sbi->s_bal_ex_scanned));
> seq_printf(seq, "\t\tgoal_hits: %u\n", atomic_read(&sbi->s_bal_goals));
> + seq_printf(seq, "\t\tstream_goal_hits: %u\n",
> + atomic_read(&sbi->s_bal_stream_goals));
> seq_printf(seq, "\t\tlen_goal_hits: %u\n",
> atomic_read(&sbi->s_bal_len_goals));
> seq_printf(seq, "\t\t2^n_hits: %u\n", atomic_read(&sbi->s_bal_2orders));
> --
> 2.46.1
>
On 2025/7/17 18:29, Ojaswin Mujoo wrote:
> On Mon, Jul 14, 2025 at 09:03:12PM +0800, Baokun Li wrote:
>> In ext4_mb_regular_allocator(), after the call to ext4_mb_find_by_goal()
>> fails to achieve the inode goal, allocation continues with the stream
>> allocation global goal. Currently, hits for both are combined in
>> sbi->s_bal_goals, hindering accurate optimization.
>>
>> This commit separates global goal hits into sbi->s_bal_stream_goals. Since
>> stream allocation doesn't use ac->ac_g_ex.fe_start, set fe_start to -1.
>> This prevents stream allocations from being counted in s_bal_goals. Also
>> clear EXT4_MB_HINT_TRY_GOAL to avoid calling ext4_mb_find_by_goal again.
>>
>> After adding `stream_goal_hits`, `/proc/fs/ext4/sdx/mb_stats` will show:
>>
>> mballoc:
>> reqs: 840347
>> success: 750992
>> groups_scanned: 1230506
>> cr_p2_aligned_stats:
>> hits: 21531
>> groups_considered: 411664
>> extents_scanned: 21531
>> useless_loops: 0
>> bad_suggestions: 6
>> cr_goal_fast_stats:
>> hits: 111222
>> groups_considered: 1806728
>> extents_scanned: 467908
>> useless_loops: 0
>> bad_suggestions: 13
>> cr_best_avail_stats:
>> hits: 36267
>> groups_considered: 1817631
>> extents_scanned: 156143
>> useless_loops: 0
>> bad_suggestions: 204
>> cr_goal_slow_stats:
>> hits: 106396
>> groups_considered: 5671710
>> extents_scanned: 22540056
>> useless_loops: 123747
>> cr_any_free_stats:
>> hits: 138071
>> groups_considered: 724692
>> extents_scanned: 23615593
>> useless_loops: 585
>> extents_scanned: 46804261
>> goal_hits: 1307
>> stream_goal_hits: 236317
>> len_goal_hits: 155549
>> 2^n_hits: 21531
>> breaks: 225096
>> lost: 35062
>> buddies_generated: 40/40
>> buddies_time_used: 48004
>> preallocated: 5962467
>> discarded: 4847560
>>
>> Signed-off-by: Baokun Li <libaokun1@huawei.com>
>> ---
>> fs/ext4/ext4.h | 1 +
>> fs/ext4/mballoc.c | 11 +++++++++--
>> 2 files changed, 10 insertions(+), 2 deletions(-)
>>
>> diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
>> index 9df74123e7e6..8750ace12935 100644
>> --- a/fs/ext4/ext4.h
>> +++ b/fs/ext4/ext4.h
>> @@ -1646,6 +1646,7 @@ struct ext4_sb_info {
>> atomic_t s_bal_cX_ex_scanned[EXT4_MB_NUM_CRS]; /* total extents scanned */
>> atomic_t s_bal_groups_scanned; /* number of groups scanned */
>> atomic_t s_bal_goals; /* goal hits */
>> + atomic_t s_bal_stream_goals; /* stream allocation global goal hits */
>> atomic_t s_bal_len_goals; /* len goal hits */
>> atomic_t s_bal_breaks; /* too long searches */
>> atomic_t s_bal_2orders; /* 2^order hits */
>> diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
>> index 336d65c4f6a2..f56ac477c464 100644
>> --- a/fs/ext4/mballoc.c
>> +++ b/fs/ext4/mballoc.c
>> @@ -2849,8 +2849,9 @@ ext4_mb_regular_allocator(struct ext4_allocation_context *ac)
>> /* TBD: may be hot point */
>> spin_lock(&sbi->s_md_lock);
>> ac->ac_g_ex.fe_group = sbi->s_mb_last_group;
>> - ac->ac_g_ex.fe_start = sbi->s_mb_last_start;
>> spin_unlock(&sbi->s_md_lock);
>> + ac->ac_g_ex.fe_start = -1;
>> + ac->ac_flags &= ~EXT4_MB_HINT_TRY_GOAL;
> Hey Baokun, I was a bit late to review this in v2 so I'll add the
> comment here:
>
> So this is mostly to account for retires right? Maybe rather than
> disabling goal allocation a better way to do this is resetting the
> original goal group and goal start in the retry logic of
> ext4_mb_new_blocks()? Since we drop preallocations before retrying, this
> way we might actually find our goal during the retry. Its a slim chance
> though but still feels like the right way to do it.
>
> Thoughts?
It's true that successfully acquiring the goal on retry is possible, but
the probability is too low; I think attempting the inode goal on retry is
not very meaningful. The lack of trylock logic in ext4_mb_find_by_goal()
also introduces some performance overhead.
Additionally, since preallocations might be dropped before retrying, the
inode's preallocation could also be discarded. Therefore, pa overlap needs
to be re-adjusted.
For data block allocation, we should call ext4_mb_normalize_request() to
regenerate a new ac_g_ex instead of directly resetting the original goal.
ext4_mb_normalize_request() will also determine whether to reset
EXT4_MB_HINT_TRY_GOAL.
For metadata block allocation, EXT4_MB_STREAM_ALLOC is not set, so there's
no need to worry about EXT4_MB_HINT_TRY_GOAL being cleared.
Clearing EXT4_MB_HINT_TRY_GOAL here is only to avoid inode goal allocation
with -1. If you insist that we should attempt the inode goal on retry,
I will send a separate patch to address that.
Cheers,
Baokun
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