linux-kernel - Re: [PATCH v4 2/4] mm/ksm: add sysfs knobs for advisor

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Message-Id: <867b7cff-1061-45e8-86b1-f8006ebbdf6a@app.fastmail.com>
Date: Mon, 18 Dec 2023 09:44:54 -0800
From: "Stefan Roesch" <shr@...kernel.io>
To: "David Hildenbrand" <david@...hat.com>, kernel-team@...com
Cc: "Andrew Morton" <akpm@...ux-foundation.org>, hannes@...xchg.org,
 riel@...riel.com, linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH v4 2/4] mm/ksm: add sysfs knobs for advisor



On Mon, Dec 18, 2023, at 3:25 AM, David Hildenbrand wrote:
> On 13.12.23 19:27, Stefan Roesch wrote:
>> This adds four new knobs for the KSM advisor to influence its behaviour.
>> 
>> The knobs are:
>> - advisor_mode:
>>      none:      no advisor (default)
>>      scan-time: scan time advisor
>> - advisor_max_cpu: 70 (default, cpu usage percent)
>> - advisor_min_pages_to_scan: 500 (default)
>> - advisor_max_pages_to_scan: 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 | 142 +++++++++++++++++++++++++++++++++++++++++++++++++++++--
>>   1 file changed, 139 insertions(+), 3 deletions(-)
>> 
>> diff --git a/mm/ksm.c b/mm/ksm.c
>> index 4f7b71a1f3112..f7387a6d02050 100644
>> --- a/mm/ksm.c
>> +++ b/mm/ksm.c
>> @@ -302,10 +302,10 @@ unsigned long ksm_zero_pages;
>>   static unsigned long ksm_pages_skipped;
>>   
>>   /* Don't scan more than max pages per batch. */
>> -static unsigned long ksm_advisor_max_pages = 30000;
>> +static unsigned long ksm_advisor_max_pages_to_scan = 30000;
>>   
>>   /* At least scan this many pages per batch. */
>> -static unsigned long ksm_advisor_min_pages = 500;
>> +static unsigned long ksm_advisor_min_pages_to_scan = 500;
>>   
>
> That renaming should go into the previous patch.
>

Moved it to the previous patch.

>>   /* Min CPU for scanning pages per scan */
>>   static unsigned int ksm_advisor_min_cpu =  10;
>> @@ -341,6 +341,16 @@ enum ksm_advisor_type {
>>   };
>>   static enum ksm_advisor_type ksm_advisor;
>>   
>> +static void set_advisor_defaults(void)
>> +{
>> +	if (ksm_advisor == KSM_ADVISOR_NONE) {
>> +		ksm_thread_pages_to_scan = DEFAULT_PAGES_TO_SCAN;
>> +	} else if (ksm_advisor == KSM_ADVISOR_SCAN_TIME) {
>> +		advisor_ctx = (const struct advisor_ctx){ 0 };
>> +		ksm_thread_pages_to_scan = ksm_advisor_min_pages_to_scan;
>> +	}
>> +}
>> +
>>   static inline void advisor_start_scan(void)
>>   {
>>   	if (ksm_advisor == KSM_ADVISOR_SCAN_TIME)
>> @@ -434,7 +444,7 @@ static void scan_time_advisor(void)
>>   
>>   	pages = min(pages, per_page_cost * ksm_advisor_max_cpu);
>>   	pages = max(pages, per_page_cost * ksm_advisor_min_cpu);
>> -	pages = min(pages, ksm_advisor_max_pages);
>> +	pages = min(pages, ksm_advisor_max_pages_to_scan);
>>   
>>   	/* Update advisor context */
>>   	advisor_ctx.change = change;
>> @@ -3722,6 +3732,127 @@ 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)
>> +{
>> +	const char *output;
>> +
>> +	if (ksm_advisor == KSM_ADVISOR_NONE)
>> +		output = "[none] scan-time";
>> +	else if (ksm_advisor == KSM_ADVISOR_SCAN_TIME)
>> +		output = "none [scan-time]";
>> +
>> +	return sysfs_emit(buf, "%s\n", output);
>> +}
>> +
>> +static ssize_t advisor_mode_store(struct kobject *kobj,
>> +				  struct kobj_attribute *attr, const char *buf,
>> +				  size_t count)
>> +{
>> +	if (sysfs_streq("scan-time", buf))
>> +		ksm_advisor = KSM_ADVISOR_SCAN_TIME;
>> +	else if (sysfs_streq("none", buf))
>> +		ksm_advisor = KSM_ADVISOR_NONE;
>> +	else
>> +		return -EINVAL;
>> +
>> +	/* Set advisor default values */
>> +	set_advisor_defaults();
>
> It probably makes sense to not reset the defaults if the ksm_advisor 
> didn't change.
>

Added the above change.

> Apart form that, LGTM.
>
> -- 
> Cheers,
>
> David / dhildenb