Re: [PATCHv2 13/28] thp: support file pages in zap_huge_pmd()

[Kirill A. Shutemov]

On Fri, Feb 12, 2016 at 10:33:37AM -0800, Dave Hansen wrote:
> On 02/11/2016 06:21 AM, Kirill A. Shutemov wrote:
> > For file pages we don't deposit page table on mapping: no need to
> > withdraw it.
> 
> I thought the deposit thing was to guarantee we could always do a PMD
> split.  It still seems like if you wanted to split a huge-tmpfs page,
> you'd need to first split the PMD which might need the deposited one.
> 
> Why not?

For file thp, split_huge_pmd() is implemented by clearing out the pmd: we
can setup and fill pte table later. Therefore no need to deposit page
table -- we would not use it. DAX does the same.

-- 
 Kirill A. Shutemov