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

[Minchan Kim]

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@xxxxxxxxxx> 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@xxxxxxxx> 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
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