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

David Hildenbrand
2023-12-12T18:08:03Z

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?

--
Cheers,

David / dhildenb