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

Stefan Roesch
2023-12-12T18:02:34Z

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

>> + set_advisor_defaults();
>
> That function should go to this patch.
>
>
>

I'll move it to this patch. I'll also look if I can should move init_advisor() to this
patch.

> --
> Cheers,
>
> David / dhildenb