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Date: Mon, 30 Mar 2015 18:26:52 +0300
From: "Kirill A. Shutemov" <kirill@shutemov.name>
To: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Dave Hansen <dave.hansen@intel.com>, Hugh Dickins <hughd@google.com>,
        Mel Gorman <mgorman@suse.de>, Rik van Riel <riel@redhat.com>,
        Vlastimil Babka <vbabka@suse.cz>, Christoph Lameter <cl@gentwo.org>,
        Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>,
        Steve Capper <steve.capper@linaro.org>,
        Johannes Weiner <hannes@cmpxchg.org>, Michal Hocko <mhocko@suse.cz>,
        Jerome Marchand <jmarchan@redhat.com>, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org
Subject: Re: [PATCHv4 19/24] thp, mm: use migration entries to freeze page
 counts on split
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On Mon, Mar 30, 2015 at 08:38:08PM +0530, Aneesh Kumar K.V wrote:
> ....
> ....
>  +static void freeze_page(struct anon_vma *anon_vma, struct page *page)
> > +{
> > +	struct anon_vma_chain *avc;
> > +	struct vm_area_struct *vma;
> > +	pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
> 
> So this get called only with head page, We also do
> BUG_ON(PageTail(page)) in the caller.  But
> 
> 
> > +	unsigned long addr, haddr;
> > +	unsigned long mmun_start, mmun_end;
> > +	pgd_t *pgd;
> > +	pud_t *pud;
> > +	pmd_t *pmd;
> > +	pte_t *start_pte, *pte;
> > +	spinlock_t *ptl;
> ......
> 
> 
> > +
> > +static void unfreeze_page(struct anon_vma *anon_vma, struct page *page)
> > +{
> > +	struct anon_vma_chain *avc;
> > +	pgoff_t pgoff = page_to_pgoff(page);
> 
> Why ? Can this get called for tail pages ?

It cannot. pgoff is offset of head page (and therefore whole compound
page) within rmapping.

-- 
 Kirill A. Shutemov