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Date: Tue, 19 May 2015 07:00:32 +0300
From: "Kirill A. Shutemov" <kirill@shutemov.name>
To: Vlastimil Babka <vbabka@suse.cz>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Hugh Dickins <hughd@google.com>, Dave Hansen <dave.hansen@intel.com>,
        Mel Gorman <mgorman@suse.de>, Rik van Riel <riel@redhat.com>,
        Christoph Lameter <cl@gentwo.org>,
        Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>,
        Steve Capper <steve.capper@linaro.org>,
        "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>,
        Johannes Weiner <hannes@cmpxchg.org>, Michal Hocko <mhocko@suse.cz>,
        Jerome Marchand <jmarchan@redhat.com>,
        Sasha Levin <sasha.levin@oracle.com>, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org
Subject: Re: [PATCHv5 20/28] mm: differentiate page_mapped() from
 page_mapcount() for compound pages
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On Mon, May 18, 2015 at 05:35:16PM +0200, Vlastimil Babka wrote:
> On 04/23/2015 11:03 PM, Kirill A. Shutemov wrote:
> >Let's define page_mapped() to be true for compound pages if any
> >sub-pages of the compound page is mapped (with PMD or PTE).
> >
> >On other hand page_mapcount() return mapcount for this particular small
> >page.
> >
> >This will make cases like page_get_anon_vma() behave correctly once we
> >allow huge pages to be mapped with PTE.
> >
> >Most users outside core-mm should use page_mapcount() instead of
> >page_mapped().
> 
> Does "should" mean that they do that now, or just that you would like them
> to?

I would like them to.

> Should there be a warning before the function then?

Ok.

> >Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> >Tested-by: Sasha Levin <sasha.levin@oracle.com>
> 
> >--- a/include/linux/mm.h
> >+++ b/include/linux/mm.h
> >@@ -909,7 +909,16 @@ static inline pgoff_t page_file_index(struct page *page)
> 
> (not shown in the diff)
> 
>  * Return true if this page is mapped into pagetables.
> >   */
> 
> Expand the comment? Especially if you put compound_head() there.

Ok.

> >  static inline int page_mapped(struct page *page)
> 
> Convert to proper bool while at it?

Ok.

-- 
 Kirill A. Shutemov