Re: remove mixture of non-atomic operations with page->flags which requires atomic operations to access

[William Lee Irwin III <wli@holomorphy.com>]

From: William Lee Irwin III <wli@holomorphy.com>
Date: Mon, 3 Jun 2002 03:28:09 -0700
>    It should be clearing it, I'd retransmit if there weren't other objections
>    to address...

On Mon, Jun 03, 2002 at 02:27:39AM -0700, David S. Miller wrote:
> Such as the fact that none of these operations need to
> be atomic :-)

After looking around a little bit the unique reference guarantee
plus various memory barriers surrounding it appear to suffice. But
I'm still left quite uneasy by the usage of non-atomic operations
on an atomically updated lock word. At the very least making the
operand shifted an unsigned long is needed. So this ensues:


Cheers,
Bill

===== mm/page_alloc.c 1.63 vs edited =====
--- 1.63/mm/page_alloc.c	Tue May 28 16:57:49 2002
+++ edited/mm/page_alloc.c	Mon Jun  3 03:58:59 2002
@@ -110,8 +110,8 @@
 		BUG();
 	if (PageWriteback(page))
 		BUG();
-	ClearPageDirty(page);
-	page->flags &= ~(1<<PG_referenced);
+
+	page->flags &= ~((1UL << PG_referenced) | (1UL << PG_dirty));
 
 	if (current->flags & PF_FREE_PAGES)
 		goto local_freelist;