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.

Signed-off-by: John Hubbard <jhubbard@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Ira Weiny <ira.weiny@intel.com>
Cc: Jérôme Glisse <jglisse@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Link: http://lkml.kernel.org/r/20200211001536.1027652-13-jhubbard@nvidia.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/Documentation/core-api/pin_user_pages.rst b/Documentation/core-api/pin_user_pages.rst
index 5c8a5f8..2e939ff 100644 (file)
--- a/Documentation/core-api/pin_user_pages.rst
+++ b/Documentation/core-api/pin_user_pages.rst
@@ -238,6 +238,13 @@ long-term [R]DMA pins in place, or during pin/unpin transitions.
 (...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
 ==========
 

diff --git a/mm/debug.c b/mm/debug.c
index f5ffb07..2189357 100644 (file)
--- a/mm/debug.c
+++ b/mm/debug.c
@@ -85,11 +85,22 @@ void __dump_page(struct page *page, const char *reason)
        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,