linux-kernel - Re: [PATCH 8/9] memory-hotplug: enable memory hotplug to handle hugepage

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Message-ID: <1361985415-3tashl9l-mutt-n-horiguchi@ah.jp.nec.com>
Date:	Wed, 27 Feb 2013 12:16:55 -0500
From:	Naoya Horiguchi <n-horiguchi@...jp.nec.com>
To:	gong.chen@...ux.intel.com
Cc:	linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mel@....ul.ie>, Hugh Dickins <hughd@...gle.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Andi Kleen <andi@...stfloor.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 8/9] memory-hotplug: enable memory hotplug to handle
 hugepage

On Wed, Feb 27, 2013 at 02:36:04AM -0500, Chen Gong wrote:
> On Thu, Feb 21, 2013 at 02:41:47PM -0500, Naoya Horiguchi wrote:
...
> > @@ -3158,6 +3182,25 @@ static int is_hugepage_on_freelist(struct page *hpage)
> >  	return 0;
> >  }
> >  
> > +/* Returns true for head pages of in-use hugepages, otherwise returns false. */
> > +int is_hugepage_movable(struct page *hpage)
> > +{
> > +	struct page *page;
> > +	struct page *tmp;
> > +	struct hstate *h = page_hstate(hpage);
> > +	int ret = 0;
> > +
> > +	VM_BUG_ON(!PageHuge(hpage));
> > +	if (PageTail(hpage))
> > +		return 0;
> > +	spin_lock(&hugetlb_lock);
> > +	list_for_each_entry_safe(page, tmp, &h->hugepage_activelist, lru)
> > +		if (page == hpage)
> > +			ret = 1;
> 
> I don't understand the logic here. 1) page is not removed why tmp is used?
> 2) why hitting (page ==hpage) but not breaking from the loop?

For question 1), using list_for_each_entry_safe() was a remnant of
try and error and will be fixed. And for question 2), I will add
break in later version.

Thanks,
Naoya

> > +	spin_unlock(&hugetlb_lock);
> > +	return ret;
> > +}
> > +
> > [...]
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