From dd78fedde4b99b322f2dc849d467d365a82e23ca Mon Sep 17 00:00:00 2001 From: "Kirill A. Shutemov" Date: Tue, 26 Jul 2016 15:25:26 -0700 Subject: rmap: support file thp Naive approach: on mapping/unmapping the page as compound we update ->_mapcount on each 4k page. That's not efficient, but it's not obvious how we can optimize this. We can look into optimization later. PG_double_map optimization doesn't work for file pages since lifecycle of file pages is different comparing to anon pages: file page can be mapped again at any time. Link: http://lkml.kernel.org/r/1466021202-61880-11-git-send-email-kirill.shutemov@linux.intel.com Signed-off-by: Kirill A. Shutemov Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/util.c | 6 ++++++ 1 file changed, 6 insertions(+) (limited to 'mm/util.c') diff --git a/mm/util.c b/mm/util.c index b756ee36f7f0..8d010ef2ce1c 100644 --- a/mm/util.c +++ b/mm/util.c @@ -412,6 +412,12 @@ int __page_mapcount(struct page *page) int ret; ret = atomic_read(&page->_mapcount) + 1; + /* + * For file THP page->_mapcount contains total number of mapping + * of the page: no need to look into compound_mapcount. + */ + if (!PageAnon(page) && !PageHuge(page)) + return ret; page = compound_head(page); ret += atomic_read(compound_mapcount_ptr(page)) + 1; if (PageDoubleMap(page)) -- cgit