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

[David Hildenbrand]

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@xxxxxxxxxxxx>
> > > ---
> > >    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