linux-kernel - Re: [PATCH v2] mm: incorporate zero pages into transparent huge pages

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Date:	Wed, 11 Feb 2015 23:33:09 +0100
From:	Andrea Arcangeli <aarcange@...hat.com>
To:	"Kirill A. Shutemov" <kirill@...temov.name>
Cc:	Ebru Akagunduz <ebru.akagunduz@...il.com>, linux-mm@...ck.org,
	akpm@...ux-foundation.org, mhocko@...e.cz, mgorman@...e.de,
	rientjes@...gle.com, sasha.levin@...cle.com, hughd@...gle.com,
	hannes@...xchg.org, vbabka@...e.cz, linux-kernel@...r.kernel.org,
	riel@...hat.com
Subject: Re: [PATCH v2] mm: incorporate zero pages into transparent huge pages

On Thu, Feb 12, 2015 at 12:21:40AM +0200, Kirill A. Shutemov wrote:
> On Wed, Feb 11, 2015 at 11:16:00PM +0100, Andrea Arcangeli wrote:
> > On Wed, Feb 11, 2015 at 11:03:55PM +0200, Ebru Akagunduz wrote:
> > > Changes in v2:
> > >  - Check zero pfn in release_pte_pages() (Andrea Arcangeli)
> > 
> > .. and in:
> > 
> > > @@ -2237,7 +2237,7 @@ static void __collapse_huge_page_copy(pte_t *pte, struct page *page,
> > >  		pte_t pteval = *_pte;
> > >  		struct page *src_page;
> > >  
> > > -		if (pte_none(pteval)) {
> > > +		if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) {
> > >  			clear_user_highpage(page, address);
> > >  			add_mm_counter(vma->vm_mm, MM_ANONPAGES, 1);
> > >  		} else {
> > 
> > __collapse_huge_page_copy, both were needed as far as I can tell.
> 
> There was is_zero_pfn(pte_pfn(pteval)) in __collapse_huge_page_copy() in
> original patch.

That clarifies things ok.
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