Re: [RFC PATCHES 1/2] iommu: Add RCU-protected page free support

[Baolu Lu]

On 2022/6/9 20:49, Jason Gunthorpe wrote:
> > +void iommu_free_pgtbl_pages(struct iommu_domain *domain,
> > +			    struct list_head *pages)
> > +{
> > +	struct page *page, *next;
> > +
> > +	if (!domain->concurrent_traversal) {
> > +		put_pages_list(pages);
> > +		return;
> > +	}
> > +
> > +	list_for_each_entry_safe(page, next, pages, lru) {
> > +		list_del(&page->lru);
> > +		call_rcu(&page->rcu_head, pgtble_page_free_rcu);
> > +	}
> It seems OK, but I wonder if there is benifit to using
> put_pages_list() from the rcu callback

The price is that we need to allocate a "struct list_head" and free it
in the rcu callback as well. Currently the list_head is sitting in the
stack.

Best regards,
baolu