Re: [PATCH v3 09/12] mm: dump_page(): better diagnostics for huge pinned pages

Jan Kara
2020-02-03T14:44:59Z

On Fri 31-01-20 19:40:26, 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.
>
> Signed-off-by: John Hubbard <jhubbard@nvidia.com>

Looks good to me. You can add:

Reviewed-by: Jan Kara <jack@suse.cz>

Honza

> ---
> Documentation/core-api/pin_user_pages.rst | 7 +++++
> mm/debug.c | 34 +++++++++++++++++------
> 2 files changed, 33 insertions(+), 8 deletions(-)
>
> diff --git a/Documentation/core-api/pin_user_pages.rst b/Documentation/core-api/pin_user_pages.rst
> index 3f72b1ea1104..dd21ea140ef4 100644
> --- a/Documentation/core-api/pin_user_pages.rst
> +++ b/Documentation/core-api/pin_user_pages.rst
> @@ -215,6 +215,13 @@ Those are both going to show zero, unless CONFIG_DEBUG_VM is set. This is
> because there is a noticeable performance drop in unpin_user_page(), when they
> are activated.
>
> +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 beb1c59d784b..db81b11345be 100644
> --- a/mm/debug.c
> +++ b/mm/debug.c
> @@ -57,10 +57,20 @@ static void __dump_tail_page(struct page *page, int mapcount)
> page, page_ref_count(page), mapcount, page->mapping,
> page_to_pgoff(page));
> } else {
> - pr_warn("page:%px compound refcount:%d mapcount:%d mapping:%px "
> - "index:%#lx compound_mapcount:%d\n",
> - page, page_ref_count(head), mapcount, head->mapping,
> - page_to_pgoff(head), compound_mapcount(page));
> + if (hpage_pincount_available(page))
> + pr_warn("page:%px compound refcount:%d mapcount:%d "
> + "mapping:%px index:%#lx compound_mapcount:%d "
> + "compound_pincount:%d\n",
> + page, page_ref_count(head), mapcount,
> + head->mapping, page_to_pgoff(head),
> + compound_mapcount(page),
> + compound_pincount(page));
> + else
> + pr_warn("page:%px compound refcount:%d mapcount:%d "
> + "mapping:%px index:%#lx compound_mapcount:%d\n",
> + page, page_ref_count(head), mapcount,
> + head->mapping, page_to_pgoff(head),
> + compound_mapcount(page));
> }
>
> if (page_ref_count(page) != 0)
> @@ -103,10 +113,18 @@ void __dump_page(struct page *page, const char *reason)
>
> if (PageTail(page))
> __dump_tail_page(page, mapcount);
> - else
> - pr_warn("page:%px refcount:%d mapcount:%d mapping:%px index:%#lx\n",
> - page, page_ref_count(page), mapcount,
> - page->mapping, page_to_pgoff(page));
> + else {
> + if (hpage_pincount_available(page))
> + pr_warn("page:%px refcount:%d mapcount:%d mapping:%px "
> + "index:%#lx compound pincount: %d\n",
> + page, page_ref_count(page), mapcount,
> + page->mapping, page_to_pgoff(page),
> + compound_pincount(page));
> + else
> + pr_warn("page:%px refcount:%d mapcount:%d mapping:%px "
> + "index:%#lx\n", page, page_ref_count(page),
> + mapcount, page->mapping, page_to_pgoff(page));
> + }
> if (PageKsm(page))
> type = "ksm ";
> else if (PageAnon(page))
> --
> 2.25.0
>
--
Jan Kara <jack@suse.com>
SUSE Labs, CR