From 9996f05eac09815121bb718249f21914a667791f Mon Sep 17 00:00:00 2001 From: "Kirill A. Shutemov" Date: Fri, 7 Oct 2016 17:01:40 -0700 Subject: [PATCH] mm: clarify why we avoid page_mapcount() for slab pages in dump_page() Let's add comment on why we skip page_mapcount() for sl[aou]b pages. Link: http://lkml.kernel.org/r/20160922105532.GB24593@node Signed-off-by: Kirill A. Shutemov Acked-by: Vlastimil Babka Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/debug.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/mm/debug.c b/mm/debug.c index 74c7cae4f683..9feb699c5d25 100644 --- a/mm/debug.c +++ b/mm/debug.c @@ -42,6 +42,11 @@ const struct trace_print_flags vmaflag_names[] = { void __dump_page(struct page *page, const char *reason) { + /* + * Avoid VM_BUG_ON() in page_mapcount(). + * page->_mapcount space in struct page is used by sl[aou]b pages to + * encode own info. + */ int mapcount = PageSlab(page) ? 0 : page_mapcount(page); pr_emerg("page:%p count:%d mapcount:%d mapping:%p index:%#lx", -- 2.20.1