linux-kernel - Re: [PATCH v5 08/11] thp: setup huge zero page on non-write page fault

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Date:	Thu, 15 Nov 2012 11:32:09 +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 08/11] thp: setup huge zero page on non-write page
 fault

On Wed, Nov 14, 2012 at 03:33:16PM -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 f36bc7d..41f05f1 100644
> > --- a/mm/huge_memory.c
> > +++ b/mm/huge_memory.c
> > @@ -726,6 +726,16 @@ int do_huge_pmd_anonymous_page(struct mm_struct *mm, struct vm_area_struct *vma,
> >  			return VM_FAULT_OOM;
> >  		if (unlikely(khugepaged_enter(vma)))
> >  			return VM_FAULT_OOM;
> > +		if (!(flags & FAULT_FLAG_WRITE)) {
> > +			pgtable_t pgtable;
> > +			pgtable = pte_alloc_one(mm, haddr);
> > +			if (unlikely(!pgtable))
> > +				goto out;
> 
> No use in retrying, just return VM_FAULT_OOM.

Hm. It's consistent with non-hzp path: if pte_alloc_one() in
__do_huge_pmd_anonymous_page() fails __do_huge_pmd_anonymous_page()
returns VM_FAULT_OOM which leads to "goto out".

Should it be fixed too?

> 
> > +			spin_lock(&mm->page_table_lock);
> > +			set_huge_zero_page(pgtable, mm, vma, haddr, pmd);
> > +			spin_unlock(&mm->page_table_lock);
> > +			return 0;
> > +		}
> >  		page = alloc_hugepage_vma(transparent_hugepage_defrag(vma),
> >  					  vma, haddr, numa_node_id(), 0);
> >  		if (unlikely(!page)) {

-- 
 Kirill A. Shutemov

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