mm: fix anonymous dirtying

commit 1ac0cb5d0e22d5e483f56b2bc12172dec1cf7536 upstream.

do_anonymous_page() has been wrong to dirty the pte regardless.
If it's not going to mark the pte writable, then it won't help
to mark it dirty here, and clogs up memory with pages which will
need swap instead of being thrown away.  Especially wrong if no
overcommit is chosen, and this vma is not yet VM_ACCOUNTed -
we could exceed the limit and OOM despite no overcommit.

Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Acked-by: Rik van Riel <riel@redhat.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Nick Piggin <npiggin@suse.de>
Cc: Mel Gorman <mel@csn.ul.ie>
Cc: Minchan Kim <minchan.kim@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/mm/memory.c b/mm/memory.c
index 3856c3681fcfa94f891dedf0176963201bfe497d..1300b70f3752d15a1bf431d10506e069c9a4dd50 100644 (file)
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -2422,7 +2422,8 @@ static int do_anonymous_page(struct mm_struct *mm, struct vm_area_struct *vma,
                goto oom_free_page;
 
        entry = mk_pte(page, vma->vm_page_prot);
-       entry = maybe_mkwrite(pte_mkdirty(entry), vma);
+       if (vma->vm_flags & VM_WRITE)
+               entry = pte_mkwrite(pte_mkdirty(entry));
 
        page_table = pte_offset_map_lock(mm, pmd, address, &ptl);
        if (!pte_none(*page_table))