linux-kernel - Re: [PATCH] ext4: Modify the comment about mb_optimize

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Message-ID: <Z7wWKFrYfdJwX2JA@li-dc0c254c-257c-11b2-a85c-98b6c1322444.ibm.com>
Date: Mon, 24 Feb 2025 12:18:08 +0530
From: Ojaswin Mujoo <ojaswin@...ux.ibm.com>
To: Zizhi Wo <wozizhi@...wei.com>
Cc: linux-ext4@...r.kernel.org, jack@...e.com, tytso@....edu,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        yangerkun@...wei.com
Subject: Re: [PATCH] ext4: Modify the comment about mb_optimize_scan

On Mon, Feb 24, 2025 at 09:20:05AM +0800, 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.

Looks good Zizhi, feel free to add:

Reviewed-by: Ojaswin Mujoo <ojaswin@...ux.ibm.com>

IIRC the documentation above mballoc is a bit outdated and it might
be a good idea to see if we can make more improvements there. Maybe
something worth exploring

Regards,
ojaswin
> 
> Signed-off-by: Zizhi Wo <wozizhi@...wei.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
> -- 
> 2.39.2
>