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

[Jason Gunthorpe <jgg@nvidia.com>]

On Fri, Jun 10, 2022 at 01:37:20PM +0800, Baolu Lu wrote:
> 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.

You'd have to use a different struct page layout so that the list_head
was in the struct page and didn't overlap with the rcu_head

Jason