Provide scalable per backing_dev_info statistics counters.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
---
 include/linux/backing-dev.h |   96 +++++++++++++++++++++++++++++++++++++++++++-
 mm/backing-dev.c            |   21 +++++++++
 2 files changed, 115 insertions(+), 2 deletions(-)

Index: linux-2.6/include/linux/backing-dev.h
===================================================================
--- linux-2.6.orig/include/linux/backing-dev.h	2007-05-10 10:21:53.000000000 +0200
+++ linux-2.6/include/linux/backing-dev.h	2007-05-10 10:23:26.000000000 +0200
@@ -8,6 +8,8 @@
 #ifndef _LINUX_BACKING_DEV_H
 #define _LINUX_BACKING_DEV_H
 
+#include <linux/percpu_counter.h>
+#include <linux/log2.h>
 #include <asm/atomic.h>
 
 struct page;
@@ -24,6 +26,12 @@ enum bdi_state {
 
 typedef int (congested_fn)(void *, int);
 
+enum bdi_stat_item {
+	NR_BDI_STAT_ITEMS
+};
+
+#define BDI_STAT_BATCH (8*(1+ilog2(nr_cpu_ids)))
+
 struct backing_dev_info {
 	unsigned long ra_pages;	/* max readahead in PAGE_CACHE_SIZE units */
 	unsigned long state;	/* Always use atomic bitops on this */
@@ -32,14 +40,86 @@ struct backing_dev_info {
 	void *congested_data;	/* Pointer to aux data for congested func */
 	void (*unplug_io_fn)(struct backing_dev_info *, struct page *);
 	void *unplug_io_data;
+
+	struct percpu_counter bdi_stat[NR_BDI_STAT_ITEMS];
 };
 
-static inline void bdi_init(struct backing_dev_info *bdi)
+void bdi_init(struct backing_dev_info *bdi);
+void bdi_destroy(struct backing_dev_info *bdi);
+
+static inline void __mod_bdi_stat(struct backing_dev_info *bdi,
+		enum bdi_stat_item item, s32 amount)
+{
+	__percpu_counter_mod(&bdi->bdi_stat[item], amount, BDI_STAT_BATCH);
+}
+
+static inline void __inc_bdi_stat(struct backing_dev_info *bdi,
+		enum bdi_stat_item item)
+{
+	__mod_bdi_stat(bdi, item, 1);
+}
+
+static inline void inc_bdi_stat(struct backing_dev_info *bdi,
+		enum bdi_stat_item item)
+{
+	unsigned long flags;
+
+	local_irq_save(flags);
+	__inc_bdi_stat(bdi, item);
+	local_irq_restore(flags);
+}
+
+static inline void __dec_bdi_stat(struct backing_dev_info *bdi,
+		enum bdi_stat_item item)
 {
+	__mod_bdi_stat(bdi, item, -1);
 }
 
-static inline void bdi_destroy(struct backing_dev_info *bdi)
+static inline void dec_bdi_stat(struct backing_dev_info *bdi,
+		enum bdi_stat_item item)
 {
+	unsigned long flags;
+
+	local_irq_save(flags);
+	__dec_bdi_stat(bdi, item);
+	local_irq_restore(flags);
+}
+
+static inline s64 bdi_stat(struct backing_dev_info *bdi,
+		enum bdi_stat_item item)
+{
+	return percpu_counter_read_positive(&bdi->bdi_stat[item]);
+}
+
+static inline s64 __bdi_stat_sum(struct backing_dev_info *bdi,
+		enum bdi_stat_item item)
+{
+	return percpu_counter_sum(&bdi->bdi_stat[item]);
+}
+
+static inline s64 bdi_stat_sum(struct backing_dev_info *bdi,
+		enum bdi_stat_item item)
+{
+	s64 sum;
+	unsigned long flags;
+
+	local_irq_save(flags);
+	sum = __bdi_stat_sum(bdi, item);
+	local_irq_restore(flags);
+
+	return sum;
+}
+
+/*
+ * maximal error of a stat counter.
+ */
+static inline unsigned long bdi_stat_error(struct backing_dev_info *bdi)
+{
+#ifdef CONFIG_SMP
+	return nr_cpu_ids * BDI_STAT_BATCH;
+#else
+	return 1;
+#endif
 }
 
 /*
Index: linux-2.6/mm/backing-dev.c
===================================================================
--- linux-2.6.orig/mm/backing-dev.c	2007-05-10 10:21:46.000000000 +0200
+++ linux-2.6/mm/backing-dev.c	2007-05-10 10:23:08.000000000 +0200
@@ -5,6 +5,24 @@
 #include <linux/sched.h>
 #include <linux/module.h>
 
+void bdi_init(struct backing_dev_info *bdi)
+{
+	int i;
+
+	for (i = 0; i < NR_BDI_STAT_ITEMS; i++)
+		percpu_counter_init_irq(&bdi->bdi_stat[i], 0);
+}
+EXPORT_SYMBOL(bdi_init);
+
+void bdi_destroy(struct backing_dev_info *bdi)
+{
+	int i;
+
+	for (i = 0; i < NR_BDI_STAT_ITEMS; i++)
+		percpu_counter_destroy(&bdi->bdi_stat[i]);
+}
+EXPORT_SYMBOL(bdi_destroy);
+
 static wait_queue_head_t congestion_wqh[2] = {
 		__WAIT_QUEUE_HEAD_INITIALIZER(congestion_wqh[0]),
 		__WAIT_QUEUE_HEAD_INITIALIZER(congestion_wqh[1])

-- 

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