linux-kernel - Re: [PATCH v5 03/11] thp: copy_huge

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Date:	Thu, 15 Nov 2012 00:14:17 -0800 (PST)
From:	David Rientjes <rientjes@...gle.com>
To:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.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 03/11] thp: copy_huge_pmd(): copy huge zero page

On Thu, 15 Nov 2012, Kirill A. Shutemov wrote:

> > > @@ -778,6 +790,11 @@ int copy_huge_pmd(struct mm_struct *dst_mm, struct mm_struct *src_mm,
> > >  		pte_free(dst_mm, pgtable);
> > >  		goto out_unlock;
> > >  	}
> > > +	if (is_huge_zero_pmd(pmd)) {
> > > +		set_huge_zero_page(pgtable, dst_mm, vma, addr, dst_pmd);
> > > +		ret = 0;
> > > +		goto out_unlock;
> > > +	}
> > 
> > You said in the introduction message in this series that you still allow 
> > splitting of the pmd, so why no check for pmd_trans_splitting() before 
> > this?
> 
> pmd_trans_splitting() returns true only for pmd which points to a page
> under spliiting. It never happens with huge zero page.
> We only split a pmd to a page table without touching the page.
> mm->page_table_lock is enough to protect against that.
> 

Comment in the code?
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