On 22/05/28 07:00PM, Baokun Li wrote:
> ext4_mb_normalize_request() can move logical start of allocated blocks
> to reduce fragmentation and better utilize preallocation. However logical
> block requested as a start of allocation (ac->ac_o_ex.fe_logical) should
> always be covered by allocated blocks so we should check that by
> modifying and to or in the assertion.
>
> Signed-off-by: Baokun Li <libaokun1@xxxxxxxxxx>
Changes looks good to me as we discussed. Feel free to add -
Reviewed-by: Ritesh Harjani <ritesh.list@xxxxxxxxx>
> ---
> V1->V2:
> Change Fixes from dfe076c106f6 to c9de560ded61.
> V2->V3:
> Delete Fixes tag.
> Add more comments and commit logs to make the code easier to understand.
>
> fs/ext4/mballoc.c | 17 ++++++++++++++++-
> 1 file changed, 16 insertions(+), 1 deletion(-)
>
> diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
> index 4d3740fdff90..9e06334771a3 100644
> --- a/fs/ext4/mballoc.c
> +++ b/fs/ext4/mballoc.c
> @@ -4185,7 +4185,22 @@ ext4_mb_normalize_request(struct ext4_allocation_context *ac,
> }
> rcu_read_unlock();
>
> - if (start + size <= ac->ac_o_ex.fe_logical &&
> + /*
> + * In this function "start" and "size" are normalized for better
> + * alignment and length such that we could preallocate more blocks.
> + * This normalization is done such that original request of
> + * ac->ac_o_ex.fe_logical & fe_len should always lie within "start" and
> + * "size" boundaries.
> + * (Note fe_len can be relaxed since FS block allocation API does not
> + * provide gurantee on number of contiguous blocks allocation since that
> + * depends upon free space left, etc).
> + * In case of inode pa, later we use the allocated blocks
> + * [pa_start + fe_logical - pa_lstart, fe_len/size] from the preallocated
> + * range of goal/best blocks [start, size] to put it at the
> + * ac_o_ex.fe_logical extent of this inode.
> + * (See ext4_mb_use_inode_pa() for more details)
> + */
> + if (start + size <= ac->ac_o_ex.fe_logical ||
> start > ac->ac_o_ex.fe_logical) {
> ext4_msg(ac->ac_sb, KERN_ERR,
> "start %lu, size %lu, fe_logical %lu",
> --
> 2.31.1
>
