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.
Cc: Jan Kara <jack@xxxxxxx>
Cc: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Signed-off-by: John Hubbard <jhubbard@xxxxxxxxxx>
---
Documentation/core-api/pin_user_pages.rst | 7 +++++++
mm/debug.c | 21 ++++++++++++++++-----
2 files changed, 23 insertions(+), 5 deletions(-)
diff --git a/Documentation/core-api/pin_user_pages.rst b/Documentation/core-api/pin_user_pages.rst
index 5c8a5f89756b..2e939ff10b86 100644
--- 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 f5ffb0784559..2189357f0987 100644
--- 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,
--
2.25.0
