linux-kernel - Re: [v5][PATCH 5/6] mm: vmscan: batch shrink_page

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Date:	Wed, 5 Jun 2013 15:28:27 +0800
From:	Hillf Danton <dhillf@...il.com>
To:	Minchan Kim <minchan@...nel.org>
Cc:	Dave Hansen <dave@...1.net>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	mgorman@...e.de, tim.c.chen@...ux.intel.com
Subject: Re: [v5][PATCH 5/6] mm: vmscan: batch shrink_page_list() locking operations

On Tue, Jun 4, 2013 at 1:07 PM, Minchan Kim <minchan@...nel.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@...1.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?

> 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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