Re: [PATCHv4 15/24] mm, thp: remove infrastructure for handling splitting PMDs

[Kirill A. Shutemov]

On Sun, Mar 29, 2015 at 09:40:07PM +0530, Aneesh Kumar K.V wrote:
> "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx> writes:
> 
> > With new refcounting we don't need to mark PMDs splitting. Let's drop code
> > to handle this.
> >
> > Arch-specific code will removed separately.
> >
> 
> Can you explain this more ? Why we don't care of PMD splitting case even
> w.r.t to split_huge_page() ? 

It used to be required to keep kernel from updating page refcounts while
we splitting the page. Now with split_huge_pmd() we can split one PMD a
time without blocking refcounting. Once all PMDs split we can freeze the
page's refcounts with compound lock[1] and split underlying compound page.

[1] compound lock is replaced with migration entries by the end of the
    patchset.

-- 
 Kirill A. Shutemov
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