From: John Hubbard <jhubbard@nvidia.com>
To: "Kirill A. Shutemov" <kirill@shutemov.name>
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 11:51:11 -0800 [thread overview]
Message-ID: <a7dac2ef-8bcd-8733-538b-aaf8fd78afd0@nvidia.com> (raw)
In-Reply-To: <20200203131649.vptndo5emkzlaiew@box>
On 2/3/20 5:16 AM, Kirill A. Shutemov wrote:
> 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>
Thanks for looking through all of these!
>
> 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?
Yes: compound_nr(page) reads from the struct page, whereas MAX_ORDER_NR_PAGES
is an independent, immutable limit. When checking a struct page for corruption,
it's ideal to avoid relying on data within the struct page, as compound_nr()
would have to do.
>
>> + /*
>> + * 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.
Fixed, thanks.
thanks,
--
John Hubbard
NVIDIA
next prev parent reply other threads:[~2020-02-03 19:51 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
2020-02-03 19:51 ` John Hubbard [this message]
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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