linux-kernel - Re: [PATCH v5 07/11] thp: implement splitting pmd for huge zero page

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Date:	Thu, 15 Nov 2012 11:24:51 +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 07/11] thp: implement splitting pmd for huge zero page

On Wed, Nov 14, 2012 at 03:28:15PM -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 90e651c..f36bc7d 100644
> > --- a/mm/huge_memory.c
> > +++ b/mm/huge_memory.c
> > @@ -1611,6 +1611,7 @@ int split_huge_page(struct page *page)
> >  	struct anon_vma *anon_vma;
> >  	int ret = 1;
> >  
> > +	BUG_ON(is_huge_zero_pfn(page_to_pfn(page)));
> >  	BUG_ON(!PageAnon(page));
> >  	anon_vma = page_lock_anon_vma(page);
> >  	if (!anon_vma)
> > @@ -2509,23 +2510,63 @@ static int khugepaged(void *none)
> >  	return 0;
> >  }
> >  
> > +static void __split_huge_zero_page_pmd(struct vm_area_struct *vma,
> > +		unsigned long haddr, pmd_t *pmd)
> > +{
> 
> This entire function duplicates other code in mm/huge_memory.c which gives 
> even more incentive into breaking do_huge_pmd_wp_zero_page_fallback() into 
> logical helper functions and reusing them for both page and !page.  
> Duplicating all this code throughout the thp code just becomes a 
> maintenance nightmare down the road.

Okay, I'll try.

> > +	pgtable_t pgtable;
> > +	pmd_t _pmd;
> > +	int i;
> > +
> > +	pmdp_clear_flush(vma, haddr, pmd);
> > +	/* leave pmd empty until pte is filled */
> > +
> > +	pgtable = get_pmd_huge_pte(vma->vm_mm);
> > +	pmd_populate(vma->vm_mm, &_pmd, pgtable);
> > +
> > +	for (i = 0; i < HPAGE_PMD_NR; i++, haddr += PAGE_SIZE) {
> > +		pte_t *pte, entry;
> > +		entry = pfn_pte(my_zero_pfn(haddr), vma->vm_page_prot);
> > +		entry = pte_mkspecial(entry);
> > +		pte = pte_offset_map(&_pmd, haddr);
> > +		VM_BUG_ON(!pte_none(*pte));
> > +		set_pte_at(vma->vm_mm, haddr, pte, entry);
> > +		pte_unmap(pte);
> > +	}
> > +	smp_wmb(); /* make pte visible before pmd */
> > +	pmd_populate(vma->vm_mm, pmd, pgtable);
> > +}
> > +
> >  void __split_huge_page_pmd(struct vm_area_struct *vma, unsigned long address,
> >  		pmd_t *pmd)
> >  {
> >  	struct page *page;
> > +	struct mm_struct *mm = vma->vm_mm;
> >  	unsigned long haddr = address & HPAGE_PMD_MASK;
> > +	unsigned long mmun_start;	/* For mmu_notifiers */
> > +	unsigned long mmun_end;		/* For mmu_notifiers */
> >  
> >  	BUG_ON(vma->vm_start > haddr || vma->vm_end < haddr + HPAGE_PMD_SIZE);
> >  
> > -	spin_lock(&vma->vm_mm->page_table_lock);
> > +	mmun_start = haddr;
> > +	mmun_end   = address + HPAGE_PMD_SIZE;
> 
> address or haddr?

haddr. I'll fix.

-- 
 Kirill A. Shutemov

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