Re: [PATCH 1/3] mm, page_owner: record page owner for each subpage

From: Kirill A. Shutemov
Date: Fri Aug 16 2019 - 10:04:35 EST

On Fri, Aug 16, 2019 at 12:13:59PM +0200, Vlastimil Babka wrote:
> Currently, page owner info is only recorded for the first page of a high-order
> allocation, and copied to tail pages in the event of a split page. With the
> plan to keep previous owner info after freeing the page, it would be benefical
> to record page owner for each subpage upon allocation. This increases the
> overhead for high orders, but that should be acceptable for a debugging option.
> The order stored for each subpage is the order of the whole allocation. This
> makes it possible to calculate the "head" pfn and to recognize "tail" pages
> (quoted because not all high-order allocations are compound pages with true
> head and tail pages). When reading the page_owner debugfs file, keep skipping
> the "tail" pages so that stats gathered by existing scripts don't get inflated.
> Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx>

Hm. That's all reasonable, but I have a question: do you see how page
owner thing works for THP now?

I don't see anything in split_huge_page() path (do not confuse it with
split_page() path) that would copy the information to tail pages. Do you?

Kirill A. Shutemov