Re: [PATCH v2 1/8] mm: dump_page: print head page's refcount, for compound pages

Kirill A. Shutemov
2020-01-29T11:25:06Z

On Tue, Jan 28, 2020 at 07:24:10PM -0800, John Hubbard wrote:
> When debugging a problem that involves compound pages, it is extremely
> helpful if dump_page() reports not only the page->_refcount, but also
> the refcount of the head page of the compound page. That's because the
> head page collects refcounts for the entire compound page.
>
> Therefore, enhance dump_page() so as to print out the refcount of the
> head page of a compound page.
>
> This approach (printing information about a struct page that is not the
> struct page that was passed into dump_page()) has a precedent:
> compound_mapcount is already being printed.

refcount on a tail must always be 0. I think we should only print it when
it is non-zero, emphasizing this fact with a standalone message.

--
Kirill A. Shutemov