Re: [PATCH] ext4: Modify the comment about mb_optimize_scan

[Baokun Li <libaokun1@huawei.com>]

On 2025/2/24 9:20, Zizhi Wo wrote:
> Commit 196e402adf2e ("ext4: improve cr 0 / cr 1 group scanning") introduces
> the sysfs control interface "mb_max_linear_groups" to address the problem
> that rotational devices performance degrades when the "mb_optimize_scan"
> feature is enabled, which may result in distant block group allocation.
>
> However, the name of the interface was incorrect in the comment to the
> ext4/mballoc.c file, and this patch fixes it, without further changes.
>
> Signed-off-by: Zizhi Wo <wozizhi@huawei.com>
Looks good.

Reviewed-by: Baokun Li <libaokun1@huawei.com>
> ---
>   fs/ext4/mballoc.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
> index b25a27c86696..68b54afc78c7 100644
> --- a/fs/ext4/mballoc.c
> +++ b/fs/ext4/mballoc.c
> @@ -187,7 +187,7 @@
>    * /sys/fs/ext4/<partition>/mb_min_to_scan
>    * /sys/fs/ext4/<partition>/mb_max_to_scan
>    * /sys/fs/ext4/<partition>/mb_order2_req
> - * /sys/fs/ext4/<partition>/mb_linear_limit
> + * /sys/fs/ext4/<partition>/mb_max_linear_groups
>    *
>    * The regular allocator uses buddy scan only if the request len is power of
>    * 2 blocks and the order of allocation is >= sbi->s_mb_order2_reqs. The
> @@ -209,7 +209,7 @@
>    * get traversed linearly. That may result in subsequent allocations being not
>    * close to each other. And so, the underlying device may get filled up in a
>    * non-linear fashion. While that may not matter on non-rotational devices, for
> - * rotational devices that may result in higher seek times. "mb_linear_limit"
> + * rotational devices that may result in higher seek times. "mb_max_linear_groups"
>    * tells mballoc how many groups mballoc should search linearly before
>    * performing consulting above data structures for more efficient lookups. For
>    * non rotational devices, this value defaults to 0 and for rotational devices