linux-kernel - Re: [PATCH 7/8] memory-hotplug: enable memory hotplug to handle hugepage

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Message-ID: <1374244796-ur27gtic-mutt-n-horiguchi@ah.jp.nec.com>
Date:	Fri, 19 Jul 2013 10:39:56 -0400
From:	Naoya Horiguchi <n-horiguchi@...jp.nec.com>
To:	Hillf Danton <dhillf@...il.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 7/8] memory-hotplug: enable memory hotplug to handle
 hugepage

On Fri, Jul 19, 2013 at 01:40:38PM +0800, Hillf Danton wrote:
> On Fri, Jul 19, 2013 at 5:34 AM, Naoya Horiguchi
> <n-horiguchi@...jp.nec.com> wrote:
> > @@ -518,9 +519,11 @@ static struct page *dequeue_huge_page_node(struct hstate *h, int nid)
> >  {
> >         struct page *page;
> >
> > -       if (list_empty(&h->hugepage_freelists[nid]))
> > +       list_for_each_entry(page, &h->hugepage_freelists[nid], lru)
> > +               if (!is_migrate_isolate_page(page))
> > +                       break;
> > +       if (&h->hugepage_freelists[nid] == &page->lru)
> 
> For what is this check?

This check returns true unless a non-isolated free hugepage is found.
In "not found" case page points to h->hugepage_freelists, so without
this check successive code doesn't work fine.

Thanks,
Naoya

> >                 return NULL;
> > -       page = list_entry(h->hugepage_freelists[nid].next, struct page, lru);
> >         list_move(&page->lru, &h->hugepage_activelist);
> >         set_page_refcounted(page);
> >         h->free_huge_pages--;
>
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