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

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Date:   Thu, 9 Mar 2023 13:17:04 +0100
From:   Jan Kara <jack@...e.cz>
To:     Ojaswin Mujoo <ojaswin@...ux.ibm.com>
Cc:     linux-ext4@...r.kernel.org, Theodore Ts'o <tytso@....edu>,
        Ritesh Harjani <riteshh@...ux.ibm.com>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        Jan Kara <jack@...e.cz>, Ritesh Harjani <ritesh.list@...il.com>
Subject: Re: [RFC 06/11] ext4: Add counter to track successful allocation of
 goal length

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@...ux.ibm.com>
> Reviewed-by: Ritesh Harjani (IBM) <ritesh.list@...il.com>

Looks good to me. Feel free to add:

Reviewed-by: Jan Kara <jack@...e.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@...e.com>
SUSE Labs, CR