linux-kernel - Re: [PATCH v2 2/4] mm/ksm: add sysfs knobs for advisor

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Message-ID: <b90ba995-5485-4dd3-974b-02453e67686d@redhat.com>
Date:   Mon, 20 Nov 2023 11:53:23 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Stefan Roesch <shr@...kernel.io>, kernel-team@...com
Cc:     akpm@...ux-foundation.org, hannes@...xchg.org, riel@...riel.com,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH v2 2/4] mm/ksm: add sysfs knobs for advisor

On 28.10.23 02:09, Stefan Roesch wrote:
> This adds four new knobs for the KSM advisor to influence its behaviour.
> 
> The knobs are:
> - advisor_mode:
>      0: no advisor (default)
>      1: scan time advisor
> - advisor_min_cpu: 15 (default, cpu usage percent)
> - advisor_max_cpu: 70 (default, cpu usage percent)
> - advisor_min_pages: 500 (default)
> - advisor_max_pages: 30000 (default)
> - advisor_target_scan_time: 200 (default in seconds)
> 
> The new values will take effect on the next scan round.
> 
> Signed-off-by: Stefan Roesch <shr@...kernel.io>
> ---
>   mm/ksm.c | 154 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
>   1 file changed, 154 insertions(+)
> 
> diff --git a/mm/ksm.c b/mm/ksm.c
> index e18fecfb359d..042ecaeb0beb 100644
> --- a/mm/ksm.c
> +++ b/mm/ksm.c
> @@ -351,6 +351,14 @@ static void init_advisor(void)
>   	advisor_ctx.cpu_time = 0;
>   }


[...]

>    * Use previous scan time if available, otherwise use current scan time as an
>    * approximation for the previous scan time.
> @@ -3719,6 +3727,146 @@ static ssize_t smart_scan_store(struct kobject *kobj,
>   }
>   KSM_ATTR(smart_scan);
>   
> +static ssize_t advisor_mode_show(struct kobject *kobj,
> +				 struct kobj_attribute *attr, char *buf)
> +{
> +	return sysfs_emit(buf, "%u\n", ksm_advisor);
> +}
> +
> +static ssize_t advisor_mode_store(struct kobject *kobj,
> +				  struct kobj_attribute *attr, const char *buf,
> +				  size_t count)
> +{
> +	unsigned int mode;
> +	int err;
> +
> +	err = kstrtouint(buf, 10, &mode);
> +	if (err)
> +		return -EINVAL;
> +	if (mode > KSM_ADVISOR_LAST)
> +		return -EINVAL;
> +
> +	/* Set advisor default values */
> +	ksm_advisor = mode;
> +	init_advisor();
> +	set_advisor_defaults();
> +
> +	return count;

Can we instead use human-readable strings?

"none" and "scan-time" should be clearer.

-- 
Cheers,

David / dhildenb