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@xxxxxxxxxx>
> ---
> 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
>
