mm: fix anonymous dirtying

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>
Cc: <stable@kernel.org>
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>

diff --git a/mm/memory.c b/mm/memory.c
index 6359a4f80c4a951dd1eaeb2ebbb007fde4924db6..fc38d4ed9ad9db8be8d26e26faa95ec61d4541fe 100644 (file)
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -2653,7 +2653,8 @@ 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))