Re: [RFC 06/11] ext4: Add counter to track successful allocation of goal length

Jan Kara
2023-03-09T12:17:48Z

On Fri 27-01-23 18:07:33, Ojaswin Mujoo wrote:
> Track number of allocations where the length of blocks allocated is equal to the
> length of goal blocks (post normalization). This metric could be useful if
> making changes to the allocator logic in the future as it could give us
> visibility into how often do we trim our requests.
>
> PS: ac_b_ex.fe_len might get modified due to preallocation efforts and
> hence we use ac_f_ex.fe_len instead since we want to compare how much the
> allocator was able to actually find.
>
> Signed-off-by: Ojaswin Mujoo <ojaswin@linux.ibm.com>
> Reviewed-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>

Looks good to me. Feel free to add:

Reviewed-by: Jan Kara <jack@suse.cz>

Honza

> ---
> fs/ext4/ext4.h | 1 +
> fs/ext4/mballoc.c | 3 +++
> 2 files changed, 4 insertions(+)
>
> diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
> index 4ba2c95915eb..d8fa01e54e81 100644
> --- a/fs/ext4/ext4.h
> +++ b/fs/ext4/ext4.h
> @@ -1636,6 +1636,7 @@ 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_len_goals; /* len goal hits */
> atomic_t s_bal_breaks; /* too long searches */
> atomic_t s_bal_2orders; /* 2^order hits */
> atomic_t s_bal_cr0_bad_suggestions;
> diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
> index 07a50a13751c..c4ab8f412d32 100644
> --- a/fs/ext4/mballoc.c
> +++ b/fs/ext4/mballoc.c
> @@ -2930,6 +2930,7 @@ int ext4_seq_mb_stats_show(struct seq_file *seq, void *offset)
> atomic64_read(&sbi->s_bal_cX_failed[CR3]));
> 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\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));
> seq_printf(seq, "\t\tbreaks: %u\n", atomic_read(&sbi->s_bal_breaks));
> seq_printf(seq, "\t\tlost: %u\n", atomic_read(&sbi->s_mb_lost_chunks));
> @@ -4233,6 +4234,8 @@ static void ext4_mb_collect_stats(struct ext4_allocation_context *ac)
> if (ac->ac_g_ex.fe_start == ac->ac_b_ex.fe_start &&
> ac->ac_g_ex.fe_group == ac->ac_b_ex.fe_group)
> atomic_inc(&sbi->s_bal_goals);
> + if (ac->ac_f_ex.fe_len == ac->ac_g_ex.fe_len)
> + atomic_inc(&sbi->s_bal_len_goals);
> if (ac->ac_found > sbi->s_mb_max_to_scan)
> atomic_inc(&sbi->s_bal_breaks);
> }
> --
> 2.31.1
>
--
Jan Kara <jack@suse.com>
SUSE Labs, CR