Re: [PATCH v34 2/4] virtio-balloon: VIRTIO_BALLOON_F_FREE_PAGE_HINT

[Wei Wang]

On 06/26/2018 11:56 AM, Michael S. Tsirkin wrote:
> On Tue, Jun 26, 2018 at 11:46:35AM +0800, Wei Wang wrote:

> > > > +	if (!arrays)
> > > > +		return NULL;
> > > > +
> > > > +	for (i = 0; i < max_array_num; i++) {
> > > So we are getting a ton of memory here just to free it up a bit later.
> > > Why doesn't get_from_free_page_list get the pages from free list for us?
> > > We could also avoid the 1st allocation then - just build a list
> > > of these.
> > That wouldn't be a good choice for us. If we check how the regular
> > allocation works, there are many many things we need to consider when pages
> > are allocated to users.
> > For example, we need to take care of the nr_free
> > counter, we need to check the watermark and perform the related actions.
> > Also the folks working on arch_alloc_page to monitor page allocation
> > activities would get a surprise..if page allocation is allowed to work in
> > this way.
> mm/ code is well positioned to handle all this correctly.

I'm afraid that would be a re-implementation of the alloc functions, and 
that would be much more complex than what we have. I think your idea of 
passing a list of pages is better.

Best,
Wei