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SubjectRe: 2.6.18-rc1-mm1 oops on x86_64
On Mon, 10 Jul 2006, Christoph Lameter wrote:

> Hmm... Actually we could leave __GFP_HIGHMEM at it prior value since
> GFP_ZONEMASK masks it out anyways. Need to test this though. This may
> also make some of the __GFP_DMA32 ifdefs unnecessary.

Here is the patch that fixes __GFP_DMA32 and __GFP_HIGHMEM to always
be nonzero. However, after the #ifdef in my last patch there is no
remaining instance of this left. The cure here adds some complexity:




Avoid __GFP_xx becoming 0

We sometimes do comparisons like

xx & (__GFP_x| __GFP_y)) == GFP_y
This becomes a problem if GFP_y is redefined to be zero.

Both __GFP_HIGHMEM (caused by me) and __GFP_DMA32 (was this way before)
can become zero in order to cause a fall back to ZONE_NORMAL.

We also have a GFP_MASK that is applied before indexing into the
nodelists array. We can use that mask to avoid having both become zero
and instead use the GFP_MASK to clear the respective bits before
retrieving the zonelist.

- Remove #ifdefs that cause __GFP_HIGHMEM or __GFP_DMA32 to become zero.

- GFP_MASK works nicely to cause fall back to ZONE_NORMAL except if
CONFIG_ZONE_DMA32 and !CONFIG_HIGHMEM are set. In that case the
fallback to ZONE_NORMAL does not work. So add a special case
to mmzone.h to define a special mask that switches off the highmem
bit for this particular configuration.

Signed-off-by: Christoph Lameter <clameter@sgi.com>

Index: linux-2.6.18-rc1-mm1/include/linux/gfp.h
===================================================================
--- linux-2.6.18-rc1-mm1.orig/include/linux/gfp.h 2006-07-10 09:37:56.352426085 -0700
+++ linux-2.6.18-rc1-mm1/include/linux/gfp.h 2006-07-10 09:42:44.254485171 -0700
@@ -12,17 +12,10 @@ struct vm_area_struct;
*/
/* Zone modifiers in GFP_ZONEMASK (see linux/mmzone.h - low three bits) */
#define __GFP_DMA ((__force gfp_t)0x01u)
-
-#ifdef CONFIG_HIGHMEM
#define __GFP_HIGHMEM ((__force gfp_t)0x02u)
-#else
-#define __GFP_HIGHMEM ((__force gfp_t)0x00) /* NORMAL is HIGHMEM */
-#endif

-#ifndef CONFIG_ZONE_DMA32
+#if !defined(CONFIG_ZONE_DMA32) && BITS_PER_LONG >= 64
#define __GFP_DMA32 ((__force gfp_t)0x01) /* ZONE_DMA is ZONE_DMA32 */
-#elif BITS_PER_LONG < 64
-#define __GFP_DMA32 ((__force gfp_t)0x00) /* ZONE_NORMAL is ZONE_DMA32 */
#else
#define __GFP_DMA32 ((__force gfp_t)0x04) /* Has own ZONE_DMA32 */
#endif
Index: linux-2.6.18-rc1-mm1/include/linux/mmzone.h
===================================================================
--- linux-2.6.18-rc1-mm1.orig/include/linux/mmzone.h 2006-07-10 09:37:56.424687226 -0700
+++ linux-2.6.18-rc1-mm1/include/linux/mmzone.h 2006-07-10 09:49:18.442923919 -0700
@@ -162,18 +162,33 @@ enum zone_type {
*
* NOTE! Make sure this matches the zones in <linux/gfp.h>
*/
-#define GFP_ZONETYPES ((GFP_ZONEMASK + 1) / 2 + 1) /* Loner */

#ifdef CONFIG_ZONE_DMA32
+
+#ifdef CONFIG_HIGHMEM
+#define GFP_ZONETYPES ((GFP_ZONEMASK + 1) / 2 + 1) /* Loner */
#define GFP_ZONEMASK 0x07
-#define ZONES_SHIFT 2 /* ceil(log2(MAX_NR_ZONES)) */
+#define ZONES_SHIFT 2 /* ceil(log2(MAX_NR_ZONES)) */
+#else
+#define GFP_ZONETYPES ((0x07 + 1) / 2 + 1) /* Loner */
+/* Mask __GFP_HIGHMEM */
+#define GFP_ZONEMASK 0x05
+#define ZONES_SHIFT 2
+#endif
+
#else
#ifdef CONFIG_HIGHMEM
+
#define GFP_ZONEMASK 0x03
-#define ZONES_SHIFT 2
+#define ZONES_SHIFT 2
+#define GFP_ZONETYPES 3
+
#else
+
#define GFP_ZONEMASK 0x01
#define ZONES_SHIFT 1
+#define GFP_ZONETYPES 2
+
#endif
#endif

-
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