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From: John Hubbard <jhubbard@nvidia.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: "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>,
	"Kirill A . Shutemov" <kirill@shutemov.name>,
	"Michal Hocko" <mhocko@suse.com>,
	"Mike Kravetz" <mike.kravetz@oracle.com>,
	"Shuah Khan" <shuah@kernel.org>,
	"Vlastimil Babka" <vbabka@suse.cz>,
	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>,
	"John Hubbard" <jhubbard@nvidia.com>
Subject: [PATCH v2 1/8] mm: dump_page: print head page's refcount, for compound pages
Date: Tue, 28 Jan 2020 19:24:10 -0800
Message-ID: <20200129032417.3085670-2-jhubbard@nvidia.com> (raw)
In-Reply-To: <20200129032417.3085670-1-jhubbard@nvidia.com>

When debugging a problem that involves compound pages, it is extremely
helpful if dump_page() reports not only the page->_refcount, but also
the refcount of the head page of the compound page. That's because the
head page collects refcounts for the entire compound page.

Therefore, enhance dump_page() so as to print out the refcount of the
head page of a compound page.

This approach (printing information about a struct page that is not the
struct page that was passed into dump_page()) has a precedent:
compound_mapcount is already being printed.

Signed-off-by: John Hubbard <jhubbard@nvidia.com>
---
 mm/debug.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/mm/debug.c b/mm/debug.c
index a90da5337c14..4cc6cad8385d 100644
--- a/mm/debug.c
+++ b/mm/debug.c
@@ -76,9 +76,11 @@ 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,
+		pr_warn("page:%px refcount:%d head refcount:%d "
+			"mapcount:%d mapping:%px index:%#lx "
+			"compound_mapcount:%d\n",
+			page, page_ref_count(page),
+			page_ref_count(compound_head(page)), mapcount,
 			page->mapping, page_to_pgoff(page),
 			compound_mapcount(page));
 	else
-- 
2.25.0


  reply index

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-01-29  3:24 [PATCH v2 0/8] mm/gup: track FOLL_PIN pages (follow on from v12) John Hubbard
2020-01-29  3:24 ` John Hubbard [this message]
2020-01-29 11:25   ` [PATCH v2 1/8] mm: dump_page: print head page's refcount, for compound pages Kirill A. Shutemov
2020-01-29 22:26     ` John Hubbard
2020-01-29 22:59       ` Matthew Wilcox
2020-01-30  6:23         ` John Hubbard
2020-01-30  6:30           ` John Hubbard
2020-01-29  3:24 ` [PATCH v2 2/8] mm/gup: split get_user_pages_remote() into two routines John Hubbard
2020-01-29  3:24 ` [PATCH v2 3/8] mm/gup: pass a flags arg to __gup_device_* functions John Hubbard
2020-01-29  3:24 ` [PATCH v2 4/8] mm/gup: track FOLL_PIN pages John Hubbard
2020-01-29 13:51   ` Kirill A. Shutemov
2020-01-30  6:44     ` John Hubbard
2020-01-30 11:31       ` Kirill A. Shutemov
2020-01-31  3:19         ` John Hubbard
2020-01-29  3:24 ` [PATCH v2 5/8] mm/gup: page->hpage_pinned_refcount: exact pin counts for huge pages John Hubbard
2020-01-29  3:24 ` [PATCH v2 6/8] mm/gup: /proc/vmstat: pin_user_pages (FOLL_PIN) reporting John Hubbard
2020-01-29  3:24 ` [PATCH v2 7/8] mm/gup_benchmark: support pin_user_pages() and related calls John Hubbard
2020-01-29  3:24 ` [PATCH v2 8/8] selftests/vm: run_vmtests: invoke gup_benchmark with basic FOLL_PIN coverage John Hubbard

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