[patch 20/21] optimise layout of struct zone

Andrew Morton (akpm@zip.com.au)
Sun, 11 Aug 2002 00:40:16 -0700


Use the new max cache alignment to optimise the layout of struct zone.

struct zone goes from ~270 bytes (UP) to 768 bytes (SMP, x86). This is
not a trick which should be generally used.

mmzone.h | 23 ++++++++++++++++++++++-
1 files changed, 22 insertions(+), 1 deletion(-)

--- 2.5.31/include/linux/mmzone.h~zone-lock-alignment Sun Aug 11 00:20:35 2002
+++ 2.5.31-akpm/include/linux/mmzone.h Sun Aug 11 00:20:50 2002
@@ -8,6 +8,7 @@
#include <linux/spinlock.h>
#include <linux/list.h>
#include <linux/wait.h>
+#include <linux/cache.h>
#include <asm/atomic.h>

/*
@@ -28,6 +29,21 @@ typedef struct free_area_struct {
struct pglist_data;

/*
+ * zone->lock and zone->lru_lock are two of the hottest locks in the kernel.
+ * So add a wild amount of padding here to ensure that they fall into separate
+ * cachelines. There are very few zone structures in the machine, so space
+ * consumption is not a concern here.
+ */
+#if defined(CONFIG_SMP)
+struct zone_padding {
+ int x;
+} ____cacheline_maxaligned_in_smp;
+#define ZONE_PADDING(name) struct zone_padding name;
+#else
+#define ZONE_PADDING(name)
+#endif
+
+/*
* On machines where it is needed (eg PCs) we divide physical memory
* into multiple physical zones. On a PC we have 3 zones:
*
@@ -35,6 +51,7 @@ struct pglist_data;
* ZONE_NORMAL 16-896 MB direct mapped by the kernel
* ZONE_HIGHMEM > 896 MB only page cache and user processes
*/
+
struct zone {
/*
* Commonly accessed fields:
@@ -44,6 +61,8 @@ struct zone {
unsigned long pages_min, pages_low, pages_high;
int need_balance;

+ ZONE_PADDING(_pad1_)
+
spinlock_t lru_lock;
struct list_head active_list;
struct list_head inactive_list;
@@ -51,6 +70,8 @@ struct zone {
unsigned long nr_active;
unsigned long nr_inactive;

+ ZONE_PADDING(_pad2_)
+
/*
* free areas of different sizes
*/
@@ -97,7 +118,7 @@ struct zone {
*/
char *name;
unsigned long size;
-};
+} ____cacheline_maxaligned_in_smp;

#define ZONE_DMA 0
#define ZONE_NORMAL 1

.
-
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