Re: [v5][PATCH 5/6] mm: vmscan: batch shrink_page_list() locking operations

Minchan Kim
2013-06-05T07:57:16Z

On Wed, Jun 05, 2013 at 03:28:27PM +0800, Hillf Danton wrote:
> On Tue, Jun 4, 2013 at 1:07 PM, Minchan Kim <minchan@kernel.org> wrote:
> > On Tue, Jun 04, 2013 at 09:17:26AM +0800, Hillf Danton wrote:
> >> On Tue, Jun 4, 2013 at 4:02 AM, Dave Hansen <dave@sr71.net> wrote:
> >> > +/*
> >> > + * pages come in here (via remove_list) locked and leave unlocked
> >> > + * (on either ret_pages or free_pages)
> >> > + *
> >> > + * We do this batching so that we free batches of pages with a
> >> > + * single mapping->tree_lock acquisition/release. This optimization
> >> > + * only makes sense when the pages on remove_list all share a
> >> > + * page_mapping(). If this is violated you will BUG_ON().
> >> > + */
> >> > +static int __remove_mapping_batch(struct list_head *remove_list,
> >> > + struct list_head *ret_pages,
> >> > + struct list_head *free_pages)
> >> > +{
> >> > + int nr_reclaimed = 0;
> >> > + struct address_space *mapping;
> >> > + struct page *page;
> >> > + LIST_HEAD(need_free_mapping);
> >> > +
> >> > + if (list_empty(remove_list))
> >> > + return 0;
> >> > +
> >> > + mapping = page_mapping(lru_to_page(remove_list));
> >> > + spin_lock_irq(&mapping->tree_lock);
> >> > + while (!list_empty(remove_list)) {
> >> > + page = lru_to_page(remove_list);
> >> > + BUG_ON(!PageLocked(page));
> >> > + BUG_ON(page_mapping(page) != mapping);
> >> > + list_del(&page->lru);
> >> > +
> >> > + if (!__remove_mapping(mapping, page)) {
> >> > + unlock_page(page);
> >> > + list_add(&page->lru, ret_pages);
> >> > + continue;
> >> > + }
> >> > + list_add(&page->lru, &need_free_mapping);
> >> > + }
> >> > + spin_unlock_irq(&mapping->tree_lock);
> >> > +
> >> While reclaiming pages, can we open ears upon IRQ controller,
> >> if the page list length is over 10, or even 20?
> >
> > At the moment, it implicitly could be bounded by SWAP_CLUSTER_MAX and
>
> Could we reclaim a THP currently?

You mean that we could have (512 * SWAP_CLUSTER_MAX) pages in
page_list as worst case?
Yes but in that case, we drain batch_for_mapping_rm by [6/6] so
THP page couldn't be a problem, IMO.

--
Kind regards,
Minchan Kim