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 <[email protected]> Acked-by: Vlastimil Babka <[email protected]> Signed-off-by: Andrew Morton <[email protected]> Signed-off-by: Linus Torvalds <[email protected]>
akeromi · Oct 8, 2016 · 9996f05 · 9996f05
1 parent 8f26e0b
commit 9996f05
Showing 1 changed file with 5 additions and 0 deletions.
diff --git 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",