From: Hugh Dickins <hugh@veritas.com>
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 <hugh@veritas.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
---
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) {
_