[PATCH] reduce MAX_NR_ZONES: use enum to define zones, reformat and comment
Use enum for zones and reformat zones dependent information
Add comments explaning the use of zones and add a zones_t type for zone
numbers.
Line up information that will be #ifdefd by the following patches.
[akpm@osdl.org: comment cleanups]
Signed-off-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index f45163c..03a5a6e 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -88,14 +88,53 @@
#define zone_pcp(__z, __cpu) (&(__z)->pageset[(__cpu)])
#endif
-#define ZONE_DMA 0
-#define ZONE_DMA32 1
-#define ZONE_NORMAL 2
-#define ZONE_HIGHMEM 3
+enum zone_type {
+ /*
+ * ZONE_DMA is used when there are devices that are not able
+ * to do DMA to all of addressable memory (ZONE_NORMAL). Then we
+ * carve out the portion of memory that is needed for these devices.
+ * The range is arch specific.
+ *
+ * Some examples
+ *
+ * Architecture Limit
+ * ---------------------------
+ * parisc, ia64, sparc <4G
+ * s390 <2G
+ * arm26 <48M
+ * arm Various
+ * alpha Unlimited or 0-16MB.
+ *
+ * i386, x86_64 and multiple other arches
+ * <16M.
+ */
+ ZONE_DMA,
+ /*
+ * x86_64 needs two ZONE_DMAs because it supports devices that are
+ * only able to do DMA to the lower 16M but also 32 bit devices that
+ * can only do DMA areas below 4G.
+ */
+ ZONE_DMA32,
+ /*
+ * Normal addressable memory is in ZONE_NORMAL. DMA operations can be
+ * performed on pages in ZONE_NORMAL if the DMA devices support
+ * transfers to all addressable memory.
+ */
+ ZONE_NORMAL,
+ /*
+ * A memory area that is only addressable by the kernel through
+ * mapping portions into its own address space. This is for example
+ * used by i386 to allow the kernel to address the memory beyond
+ * 900MB. The kernel will set up special mappings (page
+ * table entries on i386) for each page that the kernel needs to
+ * access.
+ */
+ ZONE_HIGHMEM,
-#define MAX_NR_ZONES 4 /* Sync this with ZONES_SHIFT */
-#define ZONES_SHIFT 2 /* ceil(log2(MAX_NR_ZONES)) */
+ MAX_NR_ZONES
+};
+#define ZONES_SHIFT 2 /* ceil(log2(MAX_NR_ZONES)) */
/*
* When a memory allocation must conform to specific limitations (such
@@ -126,16 +165,6 @@
/* #define GFP_ZONETYPES (GFP_ZONEMASK + 1) */ /* Non-loner */
#define GFP_ZONETYPES ((GFP_ZONEMASK + 1) / 2 + 1) /* Loner */
-/*
- * On machines where it is needed (eg PCs) we divide physical memory
- * into multiple physical zones. On a 32bit PC we have 4 zones:
- *
- * ZONE_DMA < 16 MB ISA DMA capable memory
- * ZONE_DMA32 0 MB Empty
- * ZONE_NORMAL 16-896 MB direct mapped by the kernel
- * ZONE_HIGHMEM > 896 MB only page cache and user processes
- */
-
struct zone {
/* Fields commonly accessed by the page allocator */
unsigned long free_pages;
@@ -266,7 +295,6 @@
char *name;
} ____cacheline_internodealigned_in_smp;
-
/*
* The "priority" of VM scanning is how much of the queues we will scan in one
* go. A value of 12 for DEF_PRIORITY implies that we will scan 1/4096th of the
@@ -373,12 +401,12 @@
return (!!zone->present_pages);
}
-static inline int is_highmem_idx(int idx)
+static inline int is_highmem_idx(enum zone_type idx)
{
return (idx == ZONE_HIGHMEM);
}
-static inline int is_normal_idx(int idx)
+static inline int is_normal_idx(enum zone_type idx)
{
return (idx == ZONE_NORMAL);
}