On Wed, 2007-04-04 at 14:32 +0200, Miklos Szeredi wrote:
> > Preferably you'd want to be able to 'flush' the per cpu diffs or
> > something like that in cases where thresh ~< NR_CPUS * stat_diff.
> >
> > How about something like this:
>
> Yes, maybe underscores and EXPORT_SYMBOLs are a bit excessive.
probably, here is one that actually compiles and handles cpu hotplug;
albeit a bit racy - which lock does exclude cpu hotplug these days?
---
include/linux/backing-dev.h | 13 +++++++
mm/backing-dev.c | 79 ++++++++++++++++++++++++++++++++++++++++++++
mm/page-writeback.c | 4 ++
3 files changed, 96 insertions(+)
Index: linux-2.6/include/linux/backing-dev.h
===================================================================
--- linux-2.6.orig/include/linux/backing-dev.h
+++ linux-2.6/include/linux/backing-dev.h
@@ -8,6 +8,7 @@
#ifndef _LINUX_BACKING_DEV_H
#define _LINUX_BACKING_DEV_H
+#include <linux/cpumask.h>
#include <linux/spinlock.h>
#include <asm/atomic.h>
@@ -117,6 +118,13 @@ void mod_bdi_stat(struct backing_dev_inf
void inc_bdi_stat(struct backing_dev_info *bdi, enum bdi_stat_item item);
void dec_bdi_stat(struct backing_dev_info *bdi, enum bdi_stat_item item);
+void bdi_flush_stat(struct backing_dev_info *bdi, enum bdi_stat_item item);
+void bdi_flush_all(struct backing_dev_info *bdi);
+
+static inline unsigned long bdi_stat_delta(void)
+{
+ return 8UL * num_online_cpus() * ilog2(num_online_cpus());
+}
#else /* CONFIG_SMP */
static inline void __mod_bdi_stat(struct backing_dev_info *bdi,
@@ -142,6 +150,11 @@ static inline void __dec_bdi_stat(struct
#define mod_bdi_stat __mod_bdi_stat
#define inc_bdi_stat __inc_bdi_stat
#define dec_bdi_stat __dec_bdi_stat
+
+#define bdi_flush_stat(bdi, item) do { } while (0)
+#define bdi_flush_all(bdi) do { } while (0)
+
+#define bdi_stat_delta() 1UL
#endif
void bdi_stat_init(struct backing_dev_info *bdi);
Index: linux-2.6/mm/backing-dev.c
===================================================================
--- linux-2.6.orig/mm/backing-dev.c
+++ linux-2.6/mm/backing-dev.c
@@ -188,4 +188,83 @@ void dec_bdi_stat(struct backing_dev_inf
local_irq_restore(flags);
}
EXPORT_SYMBOL(dec_bdi_stat);
+
+void ___bdi_flush_stat(struct backing_dev_info *bdi, enum bdi_stat_item item,
+ int cpu)
+{
+ struct bdi_per_cpu_data *pcd = &bdi->pcd[cpu];
+ s8 *p = pcd->bdi_stat_diff + item;
+
+ bdi_stat_add(*p, bdi, item);
+ *p = 0;
+}
+
+struct bdi_flush_struct {
+ struct backing_dev_info *bdi;
+ enum bdi_stat_item item;
+};
+
+void __bdi_flush_stat(struct bdi_flush_struct *flush)
+{
+ unsigned long flags;
+
+ local_irq_save(flags);
+ ___bdi_flush_stat(flush->bdi, flush->item, smp_processor_id());
+ local_irq_restore(flags);
+}
+
+void __bdi_flush_all(struct backing_dev_info *bdi)
+{
+ unsigned long flags;
+ int i, cpu;
+
+ local_irq_save(flags);
+ cpu = smp_processor_id();
+ for (i = 0; i < NR_BDI_STAT_ITEMS; i++)
+ ___bdi_flush_stat(bdi, i, cpu);
+ local_irq_restore(flags);
+}
+
+void bdi_flush_stat(struct backing_dev_info *bdi, enum bdi_stat_item item)
+{
+ struct bdi_flush_struct flush = {
+ bdi,
+ item
+ };
+
+#ifdef CONFIG_HOTPLUG_CPU
+ cpumask_t mask;
+ int cpu;
+
+ cpus_complement(mask, cpu_online_map);
+ for_each_cpu_mask(cpu, mask) {
+ unsigned long flags;
+
+ local_irq_save(flags);
+ ___bdi_flush_stat(bdi, item, cpu);
+ local_irq_restore(flags);
+ }
+#endif
+ on_each_cpu((void (*)(void *))__bdi_flush_stat, &flush, 0, 1);
+}
+
+void bdi_flush_all(struct backing_dev_info *bdi)
+{
+#ifdef CONFIG_HOTPLUG_CPU
+ cpumask_t mask;
+ int cpu;
+
+ cpus_complement(mask, cpu_online_map);
+ for_each_cpu_mask(cpu, mask) {
+ int i;
+ unsigned long flags;
+
+ local_irq_save(flags);
+ for (i = 0; i < NR_BDI_STAT_ITEMS; i++)
+ ___bdi_flush_stat(bdi, i, cpu);
+ local_irq_restore(flags);
+ }
+#endif
+ on_each_cpu((void (*)(void *))__bdi_flush_all, bdi, 0, 1);
+}
#endif
Index: linux-2.6/mm/page-writeback.c
===================================================================
--- linux-2.6.orig/mm/page-writeback.c
+++ linux-2.6/mm/page-writeback.c
@@ -345,6 +345,10 @@ static void balance_dirty_pages(struct a
get_dirty_limits(&background_thresh, &dirty_thresh,
&bdi_thresh, bdi);
+
+ if (bdi_thresh < bdi_stat_delta())
+ bdi_flush_all(bdi);
+
bdi_nr_reclaimable = bdi_stat(bdi, BDI_DIRTY) +
bdi_stat(bdi, BDI_UNSTABLE);
if (bdi_nr_reclaimable + bdi_stat(bdi, BDI_WRITEBACK) <=
-
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