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

Jan Kara
2022-09-29T11:36:35Z

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