Re: [PATCH v4] memory_hotplug: Free pages as higher order

[Arun KS]

On 2018-10-04 20:21, Michal Hocko wrote:
> On Wed 03-10-18 19:09:39, Arun KS wrote:
> [...]
> > +static int online_pages_blocks(unsigned long start, unsigned long 
> > nr_pages)
> > +{
> > +	unsigned long end = start + nr_pages;
> > +	int order, ret, onlined_pages = 0;
> > +
> > +	while (start < end) {
> > +		order = min(MAX_ORDER - 1UL, __ffs(start));
> > +
> > +		while (start + (1UL << order) > end)
> > +			order--;
>
> this really made me scratch my head. Wouldn't it be much simpler to do
> the following?
> 		order = min(MAX_ORDER - 1, get_order(end - start))?

Yes. Much better. Will change to,

                order = min(MAX_ORDER - 1,
                        get_order(PFN_PHYS(end) - PFN_PHYS(start)));

> > +
> > +		ret = (*online_page_callback)(pfn_to_page(start), order);
> > +		if (!ret)
> > +			onlined_pages += (1UL << order);
> > +		else if (ret > 0)
> > +			onlined_pages += ret;
> > +
> > +		start += (1UL << order);
> > +	}
> > +	return onlined_pages;
> >  }
> [...]
> > -static void __init __free_pages_boot_core(struct page *page, unsigned 
> > int order)
> > +void __free_pages_core(struct page *page, unsigned int order)
> >  {
> >  	unsigned int nr_pages = 1 << order;
> >  	struct page *p = page;
> >  	unsigned int loop;
> >
> > -	prefetchw(p);
> > -	for (loop = 0; loop < (nr_pages - 1); loop++, p++) {
> > -		prefetchw(p + 1);
> > +	for (loop = 0; loop < nr_pages; loop++, p++) {
> >  		__ClearPageReserved(p);
> >  		set_page_count(p, 0);
> >  	}
> > -	__ClearPageReserved(p);
> > -	set_page_count(p, 0);
> >
> >  	page_zone(page)->managed_pages += nr_pages;
> >  	set_page_refcounted(page);
>
> I think this is wort a separate patch as it is unrelated to the patch.
Sure. Will split the patch.

Regards,
Arun