linux-kernel - Re: [PATCH 1/8] migrate: make core migration code aware of hugepage

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Date:	Fri, 19 Jul 2013 12:04:56 +0800
From:	Hillf Danton <dhillf@...il.com>
To:	Naoya Horiguchi <n-horiguchi@...jp.nec.com>
Cc:	linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mgorman@...e.de>, Hugh Dickins <hughd@...gle.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Andi Kleen <andi@...stfloor.org>,
	Michal Hocko <mhocko@...e.cz>, Rik van Riel <riel@...hat.com>,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org,
	Naoya Horiguchi <nao.horiguchi@...il.com>
Subject: Re: [PATCH 1/8] migrate: make core migration code aware of hugepage

On Fri, Jul 19, 2013 at 11:18 AM, Naoya Horiguchi
<n-horiguchi@...jp.nec.com> wrote:
>> > +bool isolate_huge_page(struct page *page, struct list_head *l)
>>
>> Can we replace the page parameter with p?
>
> Yes. Maybe it's strange to use the full name "page" for one parameter
> and an extremely shortened one "l" for another one.
>
Actually i mean the l arg could be replaced with something else ;)

>> > +
>> > +void putback_active_hugepage(struct page *page)
>> > +{
>> > +       VM_BUG_ON(!PageHead(page));
>> > +       spin_lock(&hugetlb_lock);
>> > +       list_move_tail(&page->lru, &(page_hstate(page))->hugepage_activelist);
>> > +       spin_unlock(&hugetlb_lock);
>> > +       put_page(page);
>> > +}
>> > +
>> > +void putback_active_hugepages(struct list_head *l)
>> > +{
>> > +       struct page *page;
>> > +       struct page *page2;
>> > +
>> > +       list_for_each_entry_safe(page, page2, l, lru)
>> > +               putback_active_hugepage(page);
>>
>> Can we acquire hugetlb_lock only once?
>
> I'm not sure which is the best. In general, fine-grained locking is
> preferred because other lock contenders wait less.
> Could you tell some specific reason to hold lock outside the loop?
>
No anything special, looks we can do list splice after taking lock,
then we no longer contend it.

>> > @@ -1025,7 +1029,11 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page,
>> >                 list_for_each_entry_safe(page, page2, from, lru) {
>> >                         cond_resched();
>> >
>> > -                       rc = unmap_and_move(get_new_page, private,
>> > +                       if (PageHuge(page))
>> > +                               rc = unmap_and_move_huge_page(get_new_page,
>> > +                                               private, page, pass > 2, mode);
>> > +                       else
>> > +                               rc = unmap_and_move(get_new_page, private,
>> >                                                 page, pass > 2, mode);
>> >
>> Is this hunk unclean merge?
>
> Sorry, I don't catch the point. This patch is based on v3.11-rc1 and
> the present HEAD has no changes from that release.
> Or do you mean that other trees have some conflicts? (my brief checking
> on -mm/-next didn't find that...)
>
Looks this hunk should appear in 2/8 or later, as 1/8 is focusing
on hugepage->lru?
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