Re: [PATCH] ext4: Make running and commit transaction have their own freed_data_list

[Zhang Yi]

On 2023/6/12 20:40, Jinke Han wrote:
> From: Jinke Han <hanjinke.666@xxxxxxxxxxxxx>
> 
> When releasing space in jbd, we traverse s_freed_data_list to get the
> free range belonging to the current commit transaction. In extreme cases,
> the time spent may not be small, and we have observed cases exceeding
> 10ms. This patch makes running and commit transactions manage their own
> free_data_list respectively, eliminating unnecessary traversal.
> 
> And in the callback phase of the commit transaction, no one will touch
> it except the jbd thread itself, so s_md_lock is no longer needed.
> 
> Signed-off-by: Jinke Han <hanjinke.666@xxxxxxxxxxxxx>

Thanks for the patch, it looks good to me.

Reviewed-by: Zhang Yi <yi.zhang@xxxxxxxxxx>

> ---
>  fs/ext4/ext4.h    |  2 +-
>  fs/ext4/mballoc.c | 19 +++++--------------
>  2 files changed, 6 insertions(+), 15 deletions(-)
> 
> diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
> index 813b4da098a0..356905357dc9 100644
> --- a/fs/ext4/ext4.h
> +++ b/fs/ext4/ext4.h
> @@ -1557,7 +1557,7 @@ struct ext4_sb_info {
>  	unsigned int *s_mb_maxs;
>  	unsigned int s_group_info_size;
>  	unsigned int s_mb_free_pending;
> -	struct list_head s_freed_data_list;	/* List of blocks to be freed
> +	struct list_head s_freed_data_list[2];	/* List of blocks to be freed
>  						   after commit completed */
>  	struct list_head s_discard_list;
>  	struct work_struct s_discard_work;
> diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
> index 4f2a1df98141..8fab5720a979 100644
> --- a/fs/ext4/mballoc.c
> +++ b/fs/ext4/mballoc.c
> @@ -3626,7 +3626,8 @@ int ext4_mb_init(struct super_block *sb)
>  
>  	spin_lock_init(&sbi->s_md_lock);
>  	sbi->s_mb_free_pending = 0;
> -	INIT_LIST_HEAD(&sbi->s_freed_data_list);
> +	INIT_LIST_HEAD(&sbi->s_freed_data_list[0]);
> +	INIT_LIST_HEAD(&sbi->s_freed_data_list[1]);
>  	INIT_LIST_HEAD(&sbi->s_discard_list);
>  	INIT_WORK(&sbi->s_discard_work, ext4_discard_work);
>  	atomic_set(&sbi->s_retry_alloc_pending, 0);
> @@ -3878,21 +3879,11 @@ void ext4_process_freed_data(struct super_block *sb, tid_t commit_tid)
>  	struct ext4_sb_info *sbi = EXT4_SB(sb);
>  	struct ext4_free_data *entry, *tmp;
>  	struct list_head freed_data_list;
> -	struct list_head *cut_pos = NULL;
> +	struct list_head *s_freed_head = &sbi->s_freed_data_list[commit_tid & 1];
>  	bool wake;
>  
>  	INIT_LIST_HEAD(&freed_data_list);
> -
> -	spin_lock(&sbi->s_md_lock);
> -	list_for_each_entry(entry, &sbi->s_freed_data_list, efd_list) {
> -		if (entry->efd_tid != commit_tid)
> -			break;
> -		cut_pos = &entry->efd_list;
> -	}
> -	if (cut_pos)
> -		list_cut_position(&freed_data_list, &sbi->s_freed_data_list,
> -				  cut_pos);
> -	spin_unlock(&sbi->s_md_lock);
> +	list_replace_init(s_freed_head, &freed_data_list);
>  
>  	list_for_each_entry(entry, &freed_data_list, efd_list)
>  		ext4_free_data_in_buddy(sb, entry);
> @@ -6298,7 +6289,7 @@ ext4_mb_free_metadata(handle_t *handle, struct ext4_buddy *e4b,
>  	}
>  
>  	spin_lock(&sbi->s_md_lock);
> -	list_add_tail(&new_entry->efd_list, &sbi->s_freed_data_list);
> +	list_add_tail(&new_entry->efd_list, &sbi->s_freed_data_list[new_entry->efd_tid & 1]);
>  	sbi->s_mb_free_pending += clusters;
>  	spin_unlock(&sbi->s_md_lock);
>  }
>