In 2.6.17-rc1-mm2, the patch 'pg_uncached-is-ia64-only.patch' moves the ia64-only PG_uncached flag to the high order 32-bits of the page flags, and reduces FLAGS_RESERVED to 24. This latter change interacts with SPARSEMEM to push the nodes out of the flags word. ia64 actually needs all 32 high order reserved bits to hold up to 1024 nodes in the flags along with zone info and SPARSEMEM section index. For some reason that I have not investigated [this may be a bug or a feature], pushing the node field out of the flags word increases the size of the mm/page_alloc.o data region by ~32MB. before patch:size mm/page_alloc.o text data bss dec hex filename 39506 10264 65548 115318 1c276 mm/page_alloc.o after patch: size mm/page_alloc.o text data bss dec hex filename 39650 33556504 65548 33661702 201a306 mm/page_alloc.o So, 32MB is chump change on ia64 systems, but an unnecessary waste. The stated reason for the change was to "make room for another flag on 32-bit machines." 32-bit machines themselves reserve some bits of the page flags for zone and node info-- currently 9 bits. So, we can use the upper ~8 bits of the low order flags word for 64-bit only page flags. This patch restores the 64-bit system FLAGS_RESERVED to 32 and moves the PG_uncached bit back down into the high order byte of the low order flags word. Signed-off-by: Lee Schermerhorn <lee.schermerhorn@xxxxxx> Index: linux-2.6.17-rc1-mm2/include/linux/mmzone.h =================================================================== --- linux-2.6.17-rc1-mm2.orig/include/linux/mmzone.h 2006-04-12 12:07:22.000000000 -0400 +++ linux-2.6.17-rc1-mm2/include/linux/mmzone.h 2006-04-12 12:09:26.000000000 -0400 @@ -457,7 +457,7 @@ extern struct zone *next_zone(struct zon /* * with 64 bit flags field, there's plenty of room. */ -#define FLAGS_RESERVED 24 +#define FLAGS_RESERVED 32 #else Index: linux-2.6.17-rc1-mm2/include/linux/page-flags.h =================================================================== --- linux-2.6.17-rc1-mm2.orig/include/linux/page-flags.h 2006-04-12 12:07:22.000000000 -0400 +++ linux-2.6.17-rc1-mm2/include/linux/page-flags.h 2006-04-12 12:10:57.000000000 -0400 @@ -90,7 +90,7 @@ #define PG_nosave_free 18 /* Free, should not be written */ #if (BITS_PER_LONG > 32) -#define PG_uncached 32 /* Page has been mapped as uncached */ +#define PG_uncached 24 /* Page has been mapped as uncached */ #endif /* - : send the line "unsubscribe linux-ia64" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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