On Mon, Feb 10, 2020 at 04:15:36PM -0800, John Hubbard wrote:
> As part of pin_user_pages() and related API calls, pages are
> "dma-pinned". For the case of compound pages of order > 1, the per-page
> accounting of dma pins is accomplished via the 3rd struct page in the
> compound page. In order to support debugging of any pin_user_pages()-
> related problems, enhance dump_page() so as to report the pin count
> in that case.
>
> Documentation/core-api/pin_user_pages.rst is also updated accordingly.
>
> Cc: Jan Kara <jack@xxxxxxx>
> Cc: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
> Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
> Signed-off-by: John Hubbard <jhubbard@xxxxxxxxxx>
> ---
> Documentation/core-api/pin_user_pages.rst | 7 +++++++
> mm/debug.c | 21 ++++++++++++++++-----
> 2 files changed, 23 insertions(+), 5 deletions(-)
>
> diff --git a/Documentation/core-api/pin_user_pages.rst b/Documentation/core-api/pin_user_pages.rst
> index 5c8a5f89756b..2e939ff10b86 100644
> --- a/Documentation/core-api/pin_user_pages.rst
> +++ b/Documentation/core-api/pin_user_pages.rst
> @@ -238,6 +238,13 @@ long-term [R]DMA pins in place, or during pin/unpin transitions.
> (...unless it was already out of balance due to a long-term RDMA pin being in
> place.)
>
> +Other diagnostics
> +=================
> +
> +dump_page() has been enhanced slightly, to handle these new counting fields, and
> +to better report on compound pages in general. Specifically, for compound pages
> +with order > 1, the exact (hpage_pinned_refcount) pincount is reported.
> +
> References
> ==========
>
> diff --git a/mm/debug.c b/mm/debug.c
> index f5ffb0784559..2189357f0987 100644
> --- a/mm/debug.c
> +++ b/mm/debug.c
> @@ -85,11 +85,22 @@ void __dump_page(struct page *page, const char *reason)
> mapcount = PageSlab(head) ? 0 : page_mapcount(page);
>
> if (compound)
> - pr_warn("page:%px refcount:%d mapcount:%d mapping:%p "
> - "index:%#lx head:%px order:%u compound_mapcount:%d\n",
> - page, page_ref_count(head), mapcount,
> - mapping, page_to_pgoff(page), head,
> - compound_order(head), compound_mapcount(page));
> + if (hpage_pincount_available(page)) {
> + pr_warn("page:%px refcount:%d mapcount:%d mapping:%p "
> + "index:%#lx head:%px order:%u "
> + "compound_mapcount:%d compound_pincount:%d\n",
> + page, page_ref_count(head), mapcount,
> + mapping, page_to_pgoff(page), head,
> + compound_order(head), compound_mapcount(page),
> + compound_pincount(page));
> + } else {
> + pr_warn("page:%px refcount:%d mapcount:%d mapping:%p "
> + "index:%#lx head:%px order:%u "
> + "compound_mapcount:%d\n",
> + page, page_ref_count(head), mapcount,
> + mapping, page_to_pgoff(page), head,
> + compound_order(head), compound_mapcount(page));
> + }
Have you considered using pr_cont() here. I guess it would be easier to
read.
You can use my Ack anyway.
> else
> pr_warn("page:%px refcount:%d mapcount:%d mapping:%p index:%#lx\n",
> page, page_ref_count(page), mapcount,
> --
> 2.25.0
>
--
Kirill A. Shutemov
