Messages in this thread | | | Date | Thu, 10 Jan 2019 10:09:40 +0530 | From | Arun KS <> | Subject | Re: [PATCH v7] mm/page_alloc.c: memory_hotplug: free pages as higher order |
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On 2019-01-09 21:39, Alexander Duyck wrote: > 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@codeaurora.org> >> > > Acked-by: Michal Hocko <mhocko@suse.com> >> > > Reviewed-by: Oscar Salvador <osalvador@suse.de> >> > >> > 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.
The implementation was in our downstream code. I thought this might be useful for someone else in similar situations. Considering the above mentioned reasons, I ll remove changing the return type.
Regards, Arun
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