From: Hugh Dickins Date: Wed, 22 Jun 2005 00:15:11 +0000 (-0700) Subject: [PATCH] do_wp_page: cannot share file page X-Git-Url: https://git.stricted.de/?a=commitdiff_plain;h=d296e9cd02c92e576ecce5344026a4df4353cdb2;p=GitHub%2FLineageOS%2FG12%2Fandroid_kernel_amlogic_linux-4.9.git [PATCH] do_wp_page: cannot share file page 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 Signed-off-by: Linus Torvalds --- diff --git a/mm/memory.c b/mm/memory.c index b8846cf2358a..1c0a3db78a05 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -1239,7 +1239,7 @@ static int do_wp_page(struct mm_struct *mm, struct vm_area_struct * vma, } 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) {