[049/155] mm: dump_page(): additional diagnostics for huge pinned pages

Commit Message

Andrew Morton April 2, 2020, 4:05 a.m. UTC

From: John Hubbard <[e-mail]>
Subject: mm: dump_page(): additional 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.

Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: John Hubbard <[e-mail]>
Acked-by: Kirill A. Shutemov <[e-mail]>
Cc: Jan Kara <[e-mail]>
Cc: Matthew Wilcox <[e-mail]>
Cc: Ira Weiny <[e-mail]>
Cc: Jérôme Glisse <[e-mail]>
Cc: Al Viro <[e-mail]>
Cc: Christoph Hellwig <[e-mail]>
Cc: Dan Williams <[e-mail]>
Cc: Dave Chinner <[e-mail]>
Cc: Jason Gunthorpe <[e-mail]>
Cc: Jonathan Corbet <[e-mail]>
Cc: Michal Hocko <[e-mail]>
Cc: Mike Kravetz <[e-mail]>
Cc: Shuah Khan <[e-mail]>
Cc: Vlastimil Babka <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
---

 Documentation/core-api/pin_user_pages.rst |    7 ++++++
 mm/debug.c                                |   21 +++++++++++++++-----
 2 files changed, 23 insertions(+), 5 deletions(-)

Patch

--- a/Documentation/core-api/pin_user_pages.rst~mm-dump_page-additional-diagnostics-for-huge-pinned-pages
+++ a/Documentation/core-api/pin_user_pages.rst
@@ -238,6 +238,13 @@  long-term [R]DMA pins in place, or durin
 (...unless it was already out of balance due to a long-term RDMA pin being in
 place.)
 
+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
 ==========
 
--- a/mm/debug.c~mm-dump_page-additional-diagnostics-for-huge-pinned-pages
+++ a/mm/debug.c
@@ -85,11 +85,22 @@  void __dump_page(struct page *page, cons
 	mapcount = PageSlab(head) ? 0 : page_mapcount(page);
 
 	if (compound)
-		pr_warn("page:%px refcount:%d mapcount:%d mapping:%p "
-			"index:%#lx head:%px order:%u compound_mapcount:%d\n",
-			page, page_ref_count(head), mapcount,
-			mapping, page_to_pgoff(page), head,
-			compound_order(head), compound_mapcount(page));
+		if (hpage_pincount_available(page)) {
+			pr_warn("page:%px refcount:%d mapcount:%d mapping:%p "
+				"index:%#lx head:%px order:%u "
+				"compound_mapcount:%d compound_pincount:%d\n",
+				page, page_ref_count(head), mapcount,
+				mapping, page_to_pgoff(page), head,
+				compound_order(head), compound_mapcount(page),
+				compound_pincount(page));
+		} else {
+			pr_warn("page:%px refcount:%d mapcount:%d mapping:%p "
+				"index:%#lx head:%px order:%u "
+				"compound_mapcount:%d\n",
+				page, page_ref_count(head), mapcount,
+				mapping, page_to_pgoff(page), head,
+				compound_order(head), compound_mapcount(page));
+		}
 	else
 		pr_warn("page:%px refcount:%d mapcount:%d mapping:%p index:%#lx\n",
 			page, page_ref_count(page), mapcount,