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Date: Fri, 15 May 2015 14:01:40 +0200
From: Vlastimil Babka <vbabka@suse.cz>
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To: "Kirill A. Shutemov" <kirill@shutemov.name>
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 05/28] mm: adjust FOLL_SPLIT for new refcounting
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On 05/15/2015 01:36 PM, Kirill A. Shutemov wrote:
> On Fri, May 15, 2015 at 01:05:27PM +0200, Vlastimil Babka wrote:
>> On 04/23/2015 11:03 PM, Kirill A. Shutemov wrote:
>>> We need to prepare kernel to allow transhuge pages to be mapped with
>>> ptes too. We need to handle FOLL_SPLIT in follow_page_pte().
>>>
>>> Also we use split_huge_page() directly instead of split_huge_page_pmd().
>>> split_huge_page_pmd() will gone.
>>
>> You still call split_huge_page_pmd() for the is_huge_zero_page(page) case.
>
> For huge zero page we split PMD into table of zero pages and don't touch
> compound page under it. That's what split_huge_page_pmd() (renamed into
> split_huge_pmd()) will do by the end of patchset.

Ah, I see.

>> Also, of the code around split_huge_page() you basically took from
>> split_huge_page_pmd() and open-coded into follow_page_mask(), you didn't
>> include the mmu notifier calls. Why are they needed in split_huge_page_pmd()
>> but not here?
>
> We do need mmu notifier in split_huge_page_pmd() for huge zero page. When

Oh, I guess that's obvious then... to someone, anyway. Thanks.

In that case the patch seems fine.

Acked-by: Vlastimil Babka <vbabka@suse.cz>

> we need to split compound page we go into split_huge_page() which takes
> care about mmut notifiers.
>