linux-kernel - Re: [PATCH v5 05/11] thp: change_huge_pmd(): keep huge zero page write-protected

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Message-ID: <20121115084635.GC9676@otc-wbsnb-06>
Date:	Thu, 15 Nov 2012 10:46:35 +0200
From:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To:	David Rientjes <rientjes@...gle.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Andrea Arcangeli <aarcange@...hat.com>, linux-mm@...ck.org,
	Andi Kleen <ak@...ux.intel.com>,
	"H. Peter Anvin" <hpa@...ux.intel.com>,
	linux-kernel@...r.kernel.org,
	"Kirill A. Shutemov" <kirill@...temov.name>
Subject: Re: [PATCH v5 05/11] thp: change_huge_pmd(): keep huge zero page
 write-protected

On Wed, Nov 14, 2012 at 03:12:54PM -0800, David Rientjes wrote:
> On Wed, 7 Nov 2012, Kirill A. Shutemov wrote:
> 
> > diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> > index d767a7c..05490b3 100644
> > --- a/mm/huge_memory.c
> > +++ b/mm/huge_memory.c
> > @@ -1259,6 +1259,8 @@ int change_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
> >  		pmd_t entry;
> >  		entry = pmdp_get_and_clear(mm, addr, pmd);
> >  		entry = pmd_modify(entry, newprot);
> > +		if (is_huge_zero_pmd(entry))
> > +			entry = pmd_wrprotect(entry);
> >  		set_pmd_at(mm, addr, pmd, entry);
> >  		spin_unlock(&vma->vm_mm->page_table_lock);
> >  		ret = 1;
> 
> Nack, this should be handled in pmd_modify().

I disagree. It means we will have to enable hzp per arch. Bad idea.

What's wrong with the check?

-- 
 Kirill A. Shutemov

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