Re: [PATCH v3 2/4] mm/ksm: add sysfs knobs for advisor

["Stefan Roesch" <shr@devkernel.io>]

On Tue, Dec 12, 2023, at 10:07 AM, David Hildenbrand wrote:
> On 12.12.23 19:02, Stefan Roesch wrote:
>> 
>> 
>> On Tue, Dec 12, 2023, at 5:45 AM, David Hildenbrand wrote:
>>> On 05.12.23 00:49, 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: 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@devkernel.io>
>>>> ---
>>>>    mm/ksm.c | 127 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
>>>>    1 file changed, 127 insertions(+)
>>>>
>>>> diff --git a/mm/ksm.c b/mm/ksm.c
>>>> index b27010fa2e946..18b7185bbc65b 100644
>>>> --- a/mm/ksm.c
>>>> +++ b/mm/ksm.c
>>>> @@ -3735,6 +3735,128 @@ 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 */
>>>> +	init_advisor();
>>>
>>> Is the "init_advisor()" really required?
>>>
>> 
>> The init_advisor is required for the following scenario:
>> - advisor is used
>> - advisor is turned off
>> - pages_to_scan is used and run for some time
>> - advisor is turned on again
>>     ==> Advisor would start with two high values for the first calculation
>
> Can't set_advisor_defaults() handle that?
>

Yes, I can move the

advisor_ctx = (const struct advisor_ctx){ 0 };

into set_advisor_defaults().

> -- 
> Cheers,
>
> David / dhildenb