linux-kernel - [PATCH v4 09/12] mm: dump_page(): better diagnostics for huge pinned pages

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Message-ID: <20200204234117.2974687-10-jhubbard@nvidia.com>
Date:   Tue, 4 Feb 2020 15:41:14 -0800
From:   John Hubbard <jhubbard@...dia.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
CC:     Al Viro <viro@...iv.linux.org.uk>,
        Christoph Hellwig <hch@...radead.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Dave Chinner <david@...morbit.com>,
        Ira Weiny <ira.weiny@...el.com>, Jan Kara <jack@...e.cz>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Jonathan Corbet <corbet@....net>,
        Jérôme Glisse <jglisse@...hat.com>,
        "Kirill A . Shutemov" <kirill@...temov.name>,
        Michal Hocko <mhocko@...e.com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Shuah Khan <shuah@...nel.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Matthew Wilcox <willy@...radead.org>,
        <linux-doc@...r.kernel.org>, <linux-fsdevel@...r.kernel.org>,
        <linux-kselftest@...r.kernel.org>, <linux-rdma@...r.kernel.org>,
        <linux-mm@...ck.org>, LKML <linux-kernel@...r.kernel.org>,
        John Hubbard <jhubbard@...dia.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: [PATCH v4 09/12] mm: dump_page(): better diagnostics for huge pinned pages

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.

Acked-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
Reviewed-by: Jan Kara <jack@...e.cz>
Signed-off-by: John Hubbard <jhubbard@...dia.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.
 
+Other diagnostics
+=================
+
+dump_page() has been enhanced slightly, to handle these new counting fields, 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
 ==========
 
diff --git a/mm/debug.c b/mm/debug.c
index f074077eee11..e82c878c27df 100644
--- a/mm/debug.c
+++ b/mm/debug.c
@@ -57,10 +57,20 @@ static void __dump_tail_page(struct page *page, int mapcount)
 			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));
 	}
 
 	if (page_ref_count(page) != 0) {
@@ -104,10 +114,18 @@ void __dump_page(struct page *page, const char *reason)
 
 	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 = "ksm ";
 	else if (PageAnon(page))
-- 
2.25.0