On Wed, 2019-01-09 at 11:51 +0530, Arun KS wrote:
> On 2019-01-09 03:47, Alexander Duyck wrote:
> > On Fri, 2019-01-04 at 10:31 +0530, Arun KS wrote:
> > > When freeing pages are done with higher order, time spent on
> > > coalescing
> > > pages by buddy allocator can be reduced. With section size of 256MB,
> > > hot
> > > add latency of a single section shows improvement from 50-60 ms to
> > > less
> > > than 1 ms, hence improving the hot add latency by 60 times. Modify
> > > external providers of online callback to align with the change.
> > >
> > > Signed-off-by: Arun KS <arunks@xxxxxxxxxxxxxx>
> > > Acked-by: Michal Hocko <mhocko@xxxxxxxx>
> > > Reviewed-by: Oscar Salvador <osalvador@xxxxxxx>
> >
> > Sorry, ended up encountering a couple more things that have me a bit
> > confused.
> >
> > [...]
> >
> > > diff --git a/drivers/hv/hv_balloon.c b/drivers/hv/hv_balloon.c
> > > index 5301fef..211f3fe 100644
> > > --- a/drivers/hv/hv_balloon.c
> > > +++ b/drivers/hv/hv_balloon.c
> > > @@ -771,7 +771,7 @@ static void hv_mem_hot_add(unsigned long start,
> > > unsigned long size,
> > > }
> > > }
> > >
> > > -static void hv_online_page(struct page *pg)
> > > +static int hv_online_page(struct page *pg, unsigned int order)
> > > {
> > > struct hv_hotadd_state *has;
> > > unsigned long flags;
> > > @@ -783,10 +783,12 @@ static void hv_online_page(struct page *pg)
> > > if ((pfn < has->start_pfn) || (pfn >= has->end_pfn))
> > > continue;
> > >
> > > - hv_page_online_one(has, pg);
> > > + hv_bring_pgs_online(has, pfn, (1UL << order));
> > > break;
> > > }
> > > spin_unlock_irqrestore(&dm_device.ha_lock, flags);
> > > +
> > > + return 0;
> > > }
> > >
> > > static int pfn_covered(unsigned long start_pfn, unsigned long
> > > pfn_cnt)
> >
> > So the question I have is why was a return value added to these
> > functions? They were previously void types and now they are int. What
> > is the return value expected other than 0?
>
> Earlier with returning a void there was now way for an arch code to
> denying onlining of this particular page. By using an int as return
> type, we can implement this. In one of the boards I was using, there are
> some pages which should not be onlined because they are used for other
> purposes(like secure trust zone or hypervisor).
So where is the code using that? I don't see any functions in the
kernel that are returning anything other than 0. Maybe you should hold
off on changing the return type and make that a separate patch to be
enabled when you add the new functions that can return non-zero values.
That way if someone wants to backport this they are just getting the
bits needed to enable the improved hot-plug times without adding the
extra overhead for changing the return type.
