Re: [PATCHv5 05/28] mm: adjust FOLL_SPLIT for new refcounting

[Vlastimil Babka]

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@xxxxxxx>

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

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