From: "Kirill A. Shutemov" <kirill@shutemov.name>
To: John Hubbard <jhubbard@nvidia.com>
Cc: "Andrew Morton" <akpm@linux-foundation.org>,
"Al Viro" <viro@zeniv.linux.org.uk>,
"Christoph Hellwig" <hch@infradead.org>,
"Dan Williams" <dan.j.williams@intel.com>,
"Dave Chinner" <david@fromorbit.com>,
"Ira Weiny" <ira.weiny@intel.com>, "Jan Kara" <jack@suse.cz>,
"Jason Gunthorpe" <jgg@ziepe.ca>,
"Jonathan Corbet" <corbet@lwn.net>,
"Jérôme Glisse" <jglisse@redhat.com>,
"Michal Hocko" <mhocko@suse.com>,
"Mike Kravetz" <mike.kravetz@oracle.com>,
"Shuah Khan" <shuah@kernel.org>,
"Vlastimil Babka" <vbabka@suse.cz>,
"Matthew Wilcox" <willy@infradead.org>,
linux-doc@vger.kernel.org, linux-fsdevel@vger.kernel.org,
linux-kselftest@vger.kernel.org, linux-rdma@vger.kernel.org,
linux-mm@kvack.org, LKML <linux-kernel@vger.kernel.org>,
"Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>
Subject: Re: [PATCH v3 01/12] mm: dump_page(): better diagnostics for compound pages
Date: Mon, 3 Feb 2020 16:16:49 +0300 [thread overview]
Message-ID: <20200203131649.vptndo5emkzlaiew@box> (raw)
In-Reply-To: <20200201034029.4063170-2-jhubbard@nvidia.com>
On Fri, Jan 31, 2020 at 07:40:18PM -0800, John Hubbard wrote:
> A compound page collects the refcount in the head page, while leaving
> the refcount of each tail page at zero. Therefore, when debugging a
> problem that involves compound pages, it's best to have diagnostics that
> reflect that situation. However, dump_page() is oblivious to these
> points.
>
> Change dump_page() as follows:
>
> 1) For tail pages, print relevant head page information: refcount, in
> particular. But only do this if the page is not corrupted so badly
> that the pointer to the head page is all wrong.
>
> 2) Do a separate check to catch any (rare) cases of the tail page's
> refcount being non-zero, and issue a separate, clear pr_warn() if
> that ever happens.
>
> Suggested-by: Matthew Wilcox <willy@infradead.org>
> Suggested-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> Signed-off-by: John Hubbard <jhubbard@nvidia.com>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Few nit-picks below.
> ---
> mm/debug.c | 34 ++++++++++++++++++++++++++++------
> 1 file changed, 28 insertions(+), 6 deletions(-)
>
> diff --git a/mm/debug.c b/mm/debug.c
> index ecccd9f17801..beb1c59d784b 100644
> --- a/mm/debug.c
> +++ b/mm/debug.c
> @@ -42,6 +42,32 @@ const struct trace_print_flags vmaflag_names[] = {
> {0, NULL}
> };
>
> +static void __dump_tail_page(struct page *page, int mapcount)
> +{
> + struct page *head = compound_head(page);
> +
> + if ((page < head) || (page >= head + MAX_ORDER_NR_PAGES)) {
I'm not sure if we want to use compound_nr() here instead of
MAX_ORDER_NR_PAGES. Do you have any reasonaing about it?
> + /*
> + * Page is hopelessly corrupted, so limit any reporting to
> + * information about the page itself. Do not attempt to look at
> + * the head page.
> + */
> + pr_warn("page:%px refcount:%d mapcount:%d mapping:%px "
> + "index:%#lx (corrupted tail page case)\n",
> + 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 (page_ref_count(page) != 0)
> + pr_warn("page:%px PROBLEM: non-zero refcount (==%d) on this "
> + "tail page\n", page, page_ref_count(page));
Wrap into {}, please.
> +}
> +
> void __dump_page(struct page *page, const char *reason)
> {
> struct address_space *mapping;
> @@ -75,12 +101,8 @@ void __dump_page(struct page *page, const char *reason)
> */
> mapcount = PageSlab(page) ? 0 : page_mapcount(page);
>
> - if (PageCompound(page))
> - pr_warn("page:%px refcount:%d mapcount:%d mapping:%px "
> - "index:%#lx compound_mapcount: %d\n",
> - page, page_ref_count(page), mapcount,
> - page->mapping, page_to_pgoff(page),
> - compound_mapcount(page));
> + 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,
> --
> 2.25.0
>
--
Kirill A. Shutemov
next prev parent reply other threads:[~2020-02-03 13:16 UTC|newest]
Thread overview: 43+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-01 3:40 [PATCH v3 00/12] mm/gup: track FOLL_PIN pages John Hubbard
2020-02-01 3:40 ` [PATCH v3 01/12] mm: dump_page(): better diagnostics for compound pages John Hubbard
2020-02-03 13:16 ` Kirill A. Shutemov [this message]
2020-02-03 19:51 ` John Hubbard
2020-02-01 3:40 ` [PATCH v3 02/12] mm/gup: split get_user_pages_remote() into two routines John Hubbard
2020-02-03 13:17 ` Kirill A. Shutemov
2020-02-03 14:20 ` Jan Kara
2020-02-03 21:09 ` John Hubbard
2020-02-01 3:40 ` [PATCH v3 03/12] mm/gup: pass a flags arg to __gup_device_* functions John Hubbard
2020-02-03 13:19 ` Kirill A. Shutemov
2020-02-03 19:56 ` John Hubbard
2020-02-01 3:40 ` [PATCH v3 04/12] mm: introduce page_ref_sub_return() John Hubbard
2020-02-03 13:23 ` Kirill A. Shutemov
2020-02-03 20:03 ` John Hubbard
2020-02-01 3:40 ` [PATCH v3 05/12] mm/gup: pass gup flags to two more routines John Hubbard
2020-02-03 13:24 ` Kirill A. Shutemov
2020-02-03 14:18 ` Jan Kara
2020-02-01 3:40 ` [PATCH v3 06/12] mm/gup: require FOLL_GET for get_user_pages_fast() John Hubbard
2020-02-03 13:26 ` Kirill A. Shutemov
2020-02-03 14:18 ` Jan Kara
2020-02-01 3:40 ` [PATCH v3 07/12] mm/gup: track FOLL_PIN pages John Hubbard
2020-02-03 13:40 ` Kirill A. Shutemov
2020-02-03 21:01 ` John Hubbard
2020-02-03 14:29 ` Jan Kara
2020-02-01 3:40 ` [PATCH v3 08/12] mm/gup: page->hpage_pinned_refcount: exact pin counts for huge pages John Hubbard
2020-02-03 13:45 ` Kirill A. Shutemov
2020-02-03 14:43 ` Jan Kara
2020-02-01 3:40 ` [PATCH v3 09/12] mm: dump_page(): better diagnostics for huge pinned pages John Hubbard
2020-02-03 13:46 ` Kirill A. Shutemov
2020-02-03 14:44 ` Jan Kara
2020-02-01 3:40 ` [PATCH v3 10/12] mm/gup: /proc/vmstat: pin_user_pages (FOLL_PIN) reporting John Hubbard
2020-02-03 13:53 ` Kirill A. Shutemov
2020-02-03 21:04 ` John Hubbard
2020-02-03 21:30 ` Kirill A. Shutemov
2020-02-03 21:34 ` John Hubbard
2020-02-03 23:16 ` John Hubbard
2020-02-03 23:43 ` John Hubbard
2020-02-01 3:40 ` [PATCH v3 11/12] mm/gup_benchmark: support pin_user_pages() and related calls John Hubbard
2020-02-03 13:58 ` Kirill A. Shutemov
2020-02-03 21:17 ` John Hubbard
2020-02-03 21:55 ` Kirill A. Shutemov
2020-02-03 22:07 ` John Hubbard
2020-02-01 3:40 ` [PATCH v3 12/12] selftests/vm: run_vmtests: invoke gup_benchmark with basic FOLL_PIN coverage John Hubbard
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