On Thu 01-02-24 22:18:45, Baokun Li wrote:
> When yangerkun review commit 93cdf49f6eca ("ext4: Fix best extent lstart
> adjustment logic in ext4_mb_new_inode_pa()"), it was found that the best
> extent did not completely cover the original request after adjusting the
> best extent lstart in ext4_mb_new_inode_pa() as follows:
>
> original request: 2/10(8)
> normalized request: 0/64(64)
> best extent: 0/9(9)
>
> When we check if best ex can be kept at start of goal, ac_o_ex.fe_logical
> is 2 less than the adjusted best extent logical end 9, so we think the
> adjustment is done. But obviously 0/9(9) doesn't cover 2/10(8), so we
> should determine here if the original request logical end is less than or
> equal to the adjusted best extent logical end.
>
> In addition, add a comment stating when adjusted best_ex will not cover
> the original request, and remove the duplicate assertion because adjusting
> lstart makes no change to b_ex.fe_len.
>
> Link: https://lore.kernel.org/r/3630fa7f-b432-7afd-5f79-781bc3b2c5ea@xxxxxxxxxx
> Fixes: 93cdf49f6eca ("ext4: Fix best extent lstart adjustment logic in ext4_mb_new_inode_pa()")
> Cc: stable@xxxxxxxxxx
> Signed-off-by: yangerkun <yangerkun@xxxxxxxxxx>
> Signed-off-by: Baokun Li <libaokun1@xxxxxxxxxx>
Looks good. Feel free to add:
Reviewed-by: Jan Kara <jack@xxxxxxx>
Honza
> ---
> V1->V2:
> Remove the problematic BUG_ON and add some comments.
>
> fs/ext4/mballoc.c | 17 +++++++++++------
> 1 file changed, 11 insertions(+), 6 deletions(-)
>
> diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
> index 1ea6491b6b00..20cad0676aab 100644
> --- a/fs/ext4/mballoc.c
> +++ b/fs/ext4/mballoc.c
> @@ -5148,10 +5148,16 @@ ext4_mb_new_inode_pa(struct ext4_allocation_context *ac)
> .fe_len = ac->ac_orig_goal_len,
> };
> loff_t orig_goal_end = extent_logical_end(sbi, &ex);
> + loff_t o_ex_end = extent_logical_end(sbi, &ac->ac_o_ex);
>
> - /* we can't allocate as much as normalizer wants.
> - * so, found space must get proper lstart
> - * to cover original request */
> + /*
> + * We can't allocate as much as normalizer wants, so we try
> + * to get proper lstart to cover the original request, except
> + * when the goal doesn't cover the original request as below:
> + *
> + * orig_ex:2045/2055(10), isize:8417280 -> normalized:0/2048
> + * best_ex:0/200(200) -> adjusted: 1848/2048(200)
> + */
> BUG_ON(ac->ac_g_ex.fe_logical > ac->ac_o_ex.fe_logical);
> BUG_ON(ac->ac_g_ex.fe_len < ac->ac_o_ex.fe_len);
>
> @@ -5163,7 +5169,7 @@ ext4_mb_new_inode_pa(struct ext4_allocation_context *ac)
> * 1. Check if best ex can be kept at end of goal (before
> * cr_best_avail trimmed it) and still cover original start
> * 2. Else, check if best ex can be kept at start of goal and
> - * still cover original start
> + * still cover original end
> * 3. Else, keep the best ex at start of original request.
> */
> ex.fe_len = ac->ac_b_ex.fe_len;
> @@ -5173,7 +5179,7 @@ ext4_mb_new_inode_pa(struct ext4_allocation_context *ac)
> goto adjust_bex;
>
> ex.fe_logical = ac->ac_g_ex.fe_logical;
> - if (ac->ac_o_ex.fe_logical < extent_logical_end(sbi, &ex))
> + if (o_ex_end <= extent_logical_end(sbi, &ex))
> goto adjust_bex;
>
> ex.fe_logical = ac->ac_o_ex.fe_logical;
> @@ -5181,7 +5187,6 @@ ext4_mb_new_inode_pa(struct ext4_allocation_context *ac)
> ac->ac_b_ex.fe_logical = ex.fe_logical;
>
> BUG_ON(ac->ac_o_ex.fe_logical < ac->ac_b_ex.fe_logical);
> - BUG_ON(ac->ac_o_ex.fe_len > ac->ac_b_ex.fe_len);
> BUG_ON(extent_logical_end(sbi, &ex) > orig_goal_end);
> }
>
> --
> 2.31.1
>
--
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR
