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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

  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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