Re: [PATCH v7] mm/page_alloc.c: memory_hotplug: free pages as higher order

[Arun KS]

On 2019-01-09 13:07, Michal Hocko wrote:
> On Wed 09-01-19 11:28:52, Arun KS wrote:
> > On 2019-01-08 23:43, Michal Hocko wrote:
> > > On Tue 08-01-19 09:56:09, Alexander Duyck wrote:
> > > > On Fri, 2019-01-04 at 10:31 +0530, Arun KS wrote:
> > > [...]
> > > > >  static int online_pages_range(unsigned long start_pfn, unsigned long nr_pages,
> > > > >  			void *arg)
> > > > >  {
> > > > > -	unsigned long i;
> > > > >  	unsigned long onlined_pages = *(unsigned long *)arg;
> > > > > -	struct page *page;
> > > > >
> > > > >  	if (PageReserved(pfn_to_page(start_pfn)))
> > > > > -		for (i = 0; i < nr_pages; i++) {
> > > > > -			page = pfn_to_page(start_pfn + i);
> > > > > -			(*online_page_callback)(page);
> > > > > -			onlined_pages++;
> > > > > -		}
> > > > > +		onlined_pages = online_pages_blocks(start_pfn, nr_pages);
> > > >
> > > > Shouldn't this be a "+=" instead of an "="? It seems like you are
> > > > going
> > > > to lose your count otherwise.
> > >
> > > You are right of course. I should have noticed during the review.
> > > Thanks!
> >
> > I think we don't need to. The caller function is setting onlined_pages 
> > = 0
> > before calling online_pages_range().
> > And there are no other reference to online_pages_range other than from
> > online_pages().
>
> Are you missing that we accumulate onlined_pages via
> 	*(unsigned long *)arg = onlined_pages;
> in online_pages_range?

In my testing I didn't find any problem. To match the code being 
replaced and to avoid any corner cases, it is better to use +=
Will update the patch.

Regards,
Arun