From: Hugh Dickins A small optimization to do_wp_page's check for whether to avoid copy by reusing the page already mapped. It can never share a cached file page, nor can it share a reserved page (often the empty zero page), so it's a waste of time to lock and unlock in those cases. Which nowadays can both be neatly excluded by a preliminary PageAnon test. Christoph has reported that a preliminary page_count test proved valuable for scalability here, but PageAnon covers more common cases all at once. Signed-off-by: Hugh Dickins Signed-off-by: Andrew Morton --- mm/memory.c | 2 +- 1 files changed, 1 insertion(+), 1 deletion(-) diff -puN mm/memory.c~do_wp_page-cannot-share-file-page mm/memory.c --- 25/mm/memory.c~do_wp_page-cannot-share-file-page Mon Jun 6 15:23:41 2005 +++ 25-akpm/mm/memory.c Mon Jun 6 15:23:41 2005 @@ -1239,7 +1239,7 @@ static int do_wp_page(struct mm_struct * } old_page = pfn_to_page(pfn); - if (!TestSetPageLocked(old_page)) { + if (PageAnon(old_page) && !TestSetPageLocked(old_page)) { int reuse = can_share_swap_page(old_page); unlock_page(old_page); if (reuse) { _