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From: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
To: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Andrea Arcangeli <aarcange@redhat.com>
Cc: 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,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Subject: Re: [PATCHv4 19/24] thp, mm: use migration entries to freeze page counts on split
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Date: Mon, 30 Mar 2015 20:38:08 +0530
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....
....
 +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 ?


-aneesh