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

On Tue, Feb 16, 2016 at 07:31:58AM -0800, Dave Hansen wrote:

On 02/16/2016 02:00 AM, Kirill A. Shutemov wrote:

quoted

On Fri, Feb 12, 2016 at 10:33:37AM -0800, Dave Hansen wrote:

quoted

On 02/11/2016 06:21 AM, Kirill A. Shutemov wrote:

quoted

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.

Ahh...  Do we just never split in any fault contexts, or do we just
retry the fault?

In fault contexts we would just continue fault handling as if we had
pmd_none().

-- 
 Kirill A. Shutemov

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>