Re: [Xen-devel] [RFC 1/3] xen/balloon: Allow allocating DMA buffers

[Oleksandr Andrushchenko]

On 05/19/2018 01:04 AM, Boris Ostrovsky wrote:
> On 05/17/2018 04:26 AM, Oleksandr Andrushchenko wrote:
> > From: Oleksandr Andrushchenko <oleksandr_andrushchenko@xxxxxxxx>
>
> A commit message would be useful.
Sure, v1 will have it
> > Signed-off-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@xxxxxxxx>
> >
> >   	for (i = 0; i < nr_pages; i++) {
> > -		page = alloc_page(gfp);
> > -		if (page == NULL) {
> > -			nr_pages = i;
> > -			state = BP_EAGAIN;
> > -			break;
> > +		if (ext_pages) {
> > +			page = ext_pages[i];
> > +		} else {
> > +			page = alloc_page(gfp);
> > +			if (page == NULL) {
> > +				nr_pages = i;
> > +				state = BP_EAGAIN;
> > +				break;
> > +			}
> >   		}
> >   		scrub_page(page);
> >   		list_add(&page->lru, &pages);
> > @@ -529,7 +565,7 @@ static enum bp_state decrease_reservation(unsigned long nr_pages, gfp_t gfp)
> >   	i = 0;
> >   	list_for_each_entry_safe(page, tmp, &pages, lru) {
> >   		/* XENMEM_decrease_reservation requires a GFN */
> > -		frame_list[i++] = xen_page_to_gfn(page);
> > +		frames[i++] = xen_page_to_gfn(page);
> >   
> >   #ifdef CONFIG_XEN_HAVE_PVMMU
> >   		/*
> > @@ -552,18 +588,22 @@ static enum bp_state decrease_reservation(unsigned long nr_pages, gfp_t gfp)
> >   #endif
> >   		list_del(&page->lru);
> >   
> > -		balloon_append(page);
> > +		if (!ext_pages)
> > +			balloon_append(page);
>
> So what you are proposing is not really ballooning. You are just
> piggybacking on existing interfaces, aren't you?
Sort of. Basically I need to {increase|decrease}_reservation, not actually
allocating ballooned pages.
Do you think I can simply EXPORT_SYMBOL for {increase|decrease}_reservation?
Any other suggestion?
> -boris
Thank you,
Oleksandr