Re: [PATCH v2 2/2] mm/ksm: fix advisor_min_pages_to_scan description

["Lorenzo Stoakes (ARM)" <ljs@kernel.org>]

On Thu, Aug 13, 2026 at 11:17:22AM +0800, Jinjiang Tu wrote:
> Both Documentation/admin-guide/mm/ksm.rst and the comment next to the
> variable definition in mm/ksm.c describe advisor_min_pages_to_scan as a
> lower limit of the pages_to_scan parameter, but that is not how the
> scan-time advisor actually uses it. commit 4e5fa4f5eff6 ("mm/ksm: add ksm
> advisor") only uses it to initialize ksm_thread_pages_to_scan when the
> scan-time advisor is enabled. This will mislead the users.
>
> The semantics of advisor_min_pages_to_scan was updated in the v2 patchset
> [1], but the documentation wasn't updated.
>
> Update the documentation and comment to match the semantics of
> advisor_min_pages_to_scan.

Umm, firstly if this were wrong you'd need to change the name of the variable
too instad of documenting it as something completely distinct.

But secondly AFAICT the logic in scan_time_advisor() suggests that it truly does
act as a minimum bound as well as being the initial value for
ksm_thread_pages_to_scan.

So this patch just looks wrong to me.

But in any case, you are making a claim here yet have provided no evidence for
it. 'It is just the initial assignment' means nothing - if the logic can then
only increase it up to the maximum value then it still acts as a minimum.

A brief look at the logic suggests so.

But in any case - the onus is on _you_ to prove that that's not happening.

And even if you could do that, since it is _intended to be a lower bound_, the
fix wouldn't be alterting comments or documentation, it would be to re-establish
the minimum as a minimum.

>
> Link: https://lore.kernel.org/linux-mm/20231028000945.2428830-2-shr@devkernel.io/ [1]

This patch repeatedly states that it is the minimum time. You have failed to
provide any analysis to suggest otherwise.

> Signed-off-by: Jinjiang Tu <tujinjiang@huawei.com>

Assisted-by: ?

> ---
>  Documentation/admin-guide/mm/ksm.rst | 4 ++--
>  mm/ksm.c                             | 2 +-
>  2 files changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/Documentation/admin-guide/mm/ksm.rst b/Documentation/admin-guide/mm/ksm.rst
> index c9f533b10f6f..c329ca747b8c 100644
> --- a/Documentation/admin-guide/mm/ksm.rst
> +++ b/Documentation/admin-guide/mm/ksm.rst
> @@ -183,8 +183,8 @@ advisor_target_scan_time
>          pages. The default value is 200 seconds.
>
>  advisor_min_pages_to_scan
> -        specifies the lower limit of the ``pages_to_scan`` parameter of the
> -        scan time advisor. The default is 500.
> +        specifies the initial value of the ``pages_to_scan`` parameter of
> +        the scan time advisor. The default is 500.
>
>  advisor_max_pages_to_scan
>          specifies the upper limit of the ``pages_to_scan`` parameter of the
> diff --git a/mm/ksm.c b/mm/ksm.c
> index 7d5b76478f0b..4a6cf8cf5d60 100644
> --- a/mm/ksm.c
> +++ b/mm/ksm.c
> @@ -342,7 +342,7 @@ static enum ksm_advisor_type ksm_advisor;
>   * Only called through the sysfs control interface:
>   */
>
> -/* At least scan this many pages per batch. */
> +/* Initial number of pages to scan per batch. */
>  static unsigned long ksm_advisor_min_pages_to_scan = 500;
>
>  static void set_advisor_defaults(void)
> --
> 2.43.0
>

--
Cheers, Lorenzo