Re: [PATCH 05/12] mm/damon/sysfs: remove probes number validation

[Kunwu Chan <kunwu.chan@gmail.com>]

On Tue,  1 Sep 2026 22:47:38 -0700 SJ Park <sj@kernel.org> wrote:

> DAMON sysfs interface is disallowing >DAMON_MAX_PROBES nr_probes input,
> since DAMON_MAX_PROBES is the upper limit of probes per DAMON context.
> The core layer is validating the upper limit again, though.  It is
> preferred to let DAMON API callers such as sysfs interface to set
> parameters in flexible ways, and do parameters validation in the core
> layer.  Drop the duplicated validation in the sysfs interface.
> 
> Signed-off-by: SJ Park <sj@kernel.org>
> ---
>  mm/damon/sysfs.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/damon/sysfs.c b/mm/damon/sysfs.c
> index 7ec14f48d157a..b576e97cbfdb8 100644
> --- a/mm/damon/sysfs.c
> +++ b/mm/damon/sysfs.c
> @@ -1479,7 +1479,7 @@ static ssize_t nr_probes_store(struct kobject *kobj,
>  
>  	if (err)
>  		return err;
> -	if (nr < 0 || nr > DAMON_MAX_PROBES)
> +	if (nr < 0)

Hi SJ,

Thanks for the cleanup.

I was wondering whether DAMON_MAX_PROBES is purely a core invariant
or also an interface constraint.

With this change, sysfs allows nr_probes larger than
DAMON_MAX_PROBES and damon_sysfs_probes_add_dirs() will start creating
probe objects before the configuration is later rejected by
damon_valid_probe_params().

Since nr_probes directly controls the number of sysfs objects created,
do we still want to keep an early check here?

I agree that the core validation is required for non-sysfs callers,
but I am not sure whether this particular limit should be duplicated
at the sysfs layer.

Thanks,
Kunwu


>  		return -EINVAL;
>  
>  	probes = container_of(kobj, struct damon_sysfs_probes, kobj);
> -- 
> 2.47.3
> 

Sent using hkml (https://github.com/sjp38/hackermail)