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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>,
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        Jonathan Corbet <corbet@lwn.net>,
        =?UTF-8?q?J=C3=A9r=C3=B4me=20Glisse?= <jglisse@redhat.com>,
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        John Hubbard <jhubbard@nvidia.com>
Subject: [PATCH v3 09/12] mm: dump_page(): better diagnostics for huge pinned pages
Date:   Fri, 31 Jan 2020 19:40:26 -0800
Message-ID: <20200201034029.4063170-10-jhubbard@nvidia.com>
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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>
---
 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.
=20
+Other diagnostics
+=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
+
+dump_page() has been enhanced slightly, to handle these new counting field=
s, 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
 =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
=20
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 map=
count)
 			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));
 	}
=20
 	if (page_ref_count(page) !=3D 0)
@@ -103,10 +113,18 @@ void __dump_page(struct page *page, const char *reaso=
n)
=20
 	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 =3D "ksm ";
 	else if (PageAnon(page))
--=20
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