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

Minchan Kim
2013-06-04T05:07:47Z

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
it's the value used by isolate_migratepages_ranges to enable IRQ.
I have no idea it's proper value to give a chace to IRQ but at least,
Dave's code doesn't break the rule.
If we need a tune for that, it could be a another patch to investigate
all of places on vmscan.c in near future.

>
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--
Kind regards,
Minchan Kim