Re: [RFC v3 5/8] ext4: Abstract out overlap fix/check logic in ext4_mb_normalize_request()

[Jan Kara <jack@suse.cz>]

On Tue 27-09-22 14:46:45, Ojaswin Mujoo wrote:
> Abstract out the logic of fixing PA overlaps in ext4_mb_normalize_request to
> improve readability of code. This also makes it easier to make changes
> to the overlap logic in future.
> 
> There are no functional changes in this patch
> 
> Signed-off-by: Ojaswin Mujoo <ojaswin@linux.ibm.com>
> Reviewed-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>

Looks good. Feel free to add:

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

								Honza

> ---
>  fs/ext4/mballoc.c | 110 +++++++++++++++++++++++++++++-----------------
>  1 file changed, 69 insertions(+), 41 deletions(-)
> 
> diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
> index d1ce34888dcc..dda9a72c81d9 100644
> --- a/fs/ext4/mballoc.c
> +++ b/fs/ext4/mballoc.c
> @@ -4008,6 +4008,74 @@ ext4_mb_pa_assert_overlap(struct ext4_allocation_context *ac,
>  	rcu_read_unlock();
>  }
>  
> +/*
> + * Given an allocation context "ac" and a range "start", "end", check
> + * and adjust boundaries if the range overlaps with any of the existing
> + * preallocatoins stored in the corresponding inode of the allocation context.
> + *
> + *Parameters:
> + *	ac			allocation context
> + *	start			start of the new range
> + *	end			end of the new range
> + */
> +static inline void
> +ext4_mb_pa_adjust_overlap(struct ext4_allocation_context *ac,
> +			 ext4_lblk_t *start, ext4_lblk_t *end)
> +{
> +	struct ext4_inode_info *ei = EXT4_I(ac->ac_inode);
> +	struct ext4_sb_info *sbi = EXT4_SB(ac->ac_sb);
> +	struct ext4_prealloc_space *tmp_pa;
> +	ext4_lblk_t new_start, new_end;
> +	ext4_lblk_t tmp_pa_start, tmp_pa_end;
> +
> +	new_start = *start;
> +	new_end = *end;
> +
> +	/* check we don't cross already preallocated blocks */
> +	rcu_read_lock();
> +	list_for_each_entry_rcu(tmp_pa, &ei->i_prealloc_list, pa_inode_list) {
> +		if (tmp_pa->pa_deleted)
> +			continue;
> +		spin_lock(&tmp_pa->pa_lock);
> +		if (tmp_pa->pa_deleted) {
> +			spin_unlock(&tmp_pa->pa_lock);
> +			continue;
> +		}
> +
> +		tmp_pa_start = tmp_pa->pa_lstart;
> +		tmp_pa_end = tmp_pa->pa_lstart + EXT4_C2B(sbi, tmp_pa->pa_len);
> +
> +		/* PA must not overlap original request */
> +		BUG_ON(!(ac->ac_o_ex.fe_logical >= tmp_pa_end ||
> +			ac->ac_o_ex.fe_logical < tmp_pa_start));
> +
> +		/* skip PAs this normalized request doesn't overlap with */
> +		if (tmp_pa_start >= new_end || tmp_pa_end <= new_start) {
> +			spin_unlock(&tmp_pa->pa_lock);
> +			continue;
> +		}
> +		BUG_ON(tmp_pa_start <= new_start && tmp_pa_end >= new_end);
> +
> +		/* adjust start or end to be adjacent to this pa */
> +		if (tmp_pa_end <= ac->ac_o_ex.fe_logical) {
> +			BUG_ON(tmp_pa_end < new_start);
> +			new_start = tmp_pa_end;
> +		} else if (tmp_pa_start > ac->ac_o_ex.fe_logical) {
> +			BUG_ON(tmp_pa_start > new_end);
> +			new_end = tmp_pa_start;
> +		}
> +		spin_unlock(&tmp_pa->pa_lock);
> +	}
> +	rcu_read_unlock();
> +
> +	/* XXX: extra loop to check we really don't overlap preallocations */
> +	ext4_mb_pa_assert_overlap(ac, new_start, new_end);
> +
> +	*start = new_start;
> +	*end = new_end;
> +	return;
> +}
> +
>  /*
>   * Normalization means making request better in terms of
>   * size and alignment
> @@ -4022,9 +4090,6 @@ ext4_mb_normalize_request(struct ext4_allocation_context *ac,
>  	loff_t size, start_off;
>  	loff_t orig_size __maybe_unused;
>  	ext4_lblk_t start;
> -	struct ext4_inode_info *ei = EXT4_I(ac->ac_inode);
> -	struct ext4_prealloc_space *tmp_pa;
> -	ext4_lblk_t tmp_pa_start, tmp_pa_end;
>  
>  	/* do normalize only data requests, metadata requests
>  	   do not need preallocation */
> @@ -4125,47 +4190,10 @@ ext4_mb_normalize_request(struct ext4_allocation_context *ac,
>  
>  	end = start + size;
>  
> -	/* check we don't cross already preallocated blocks */
> -	rcu_read_lock();
> -	list_for_each_entry_rcu(tmp_pa, &ei->i_prealloc_list, pa_inode_list) {
> -		if (tmp_pa->pa_deleted)
> -			continue;
> -		spin_lock(&tmp_pa->pa_lock);
> -		if (tmp_pa->pa_deleted) {
> -			spin_unlock(&tmp_pa->pa_lock);
> -			continue;
> -		}
> -
> -		tmp_pa_start = tmp_pa->pa_lstart;
> -		tmp_pa_end = tmp_pa->pa_lstart + EXT4_C2B(sbi, tmp_pa->pa_len);
> -
> -		/* PA must not overlap original request */
> -		BUG_ON(!(ac->ac_o_ex.fe_logical >= tmp_pa_end ||
> -			ac->ac_o_ex.fe_logical < tmp_pa_start));
> -
> -		/* skip PAs this normalized request doesn't overlap with */
> -		if (tmp_pa_start >= end || tmp_pa_end <= start) {
> -			spin_unlock(&tmp_pa->pa_lock);
> -			continue;
> -		}
> -		BUG_ON(tmp_pa_start <= start && tmp_pa_end >= end);
> +	ext4_mb_pa_adjust_overlap(ac, &start, &end);
>  
> -		/* adjust start or end to be adjacent to this pa */
> -		if (tmp_pa_end <= ac->ac_o_ex.fe_logical) {
> -			BUG_ON(tmp_pa_end < start);
> -			start = tmp_pa_end;
> -		} else if (tmp_pa_start > ac->ac_o_ex.fe_logical) {
> -			BUG_ON(tmp_pa_start > end);
> -			end = tmp_pa_start;
> -		}
> -		spin_unlock(&tmp_pa->pa_lock);
> -	}
> -	rcu_read_unlock();
>  	size = end - start;
>  
> -	/* XXX: extra loop to check we really don't overlap preallocations */
> -	ext4_mb_pa_assert_overlap(ac, start, end);
> -
>  	/*
>  	 * In this function "start" and "size" are normalized for better
>  	 * alignment and length such that we could preallocate more blocks.
> -- 
> 2.31.1
> 
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR