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Date: Wed, 04 Apr 2007 22:03:43 +0200
From: Peter Zijlstra <a.p.zijlstra@...llo.nl>
To: Miklos Szeredi <miklos@...redi.hu>
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org,
akpm@...ux-foundation.org, neilb@...e.de, dgc@....com,
tomoki.sekiyama.qu@...achi.com
Subject: Re: [PATCH 6/6] mm: per device dirty threshold
Ok, so that all wasn't really good, sending IPIs about like that on
LargeSMP will not make me any friends, so how about this:
---
include/linux/backing-dev.h | 13 ++++++++++++-
mm/backing-dev.c | 28 ++++++++++++++++++++++------
mm/page-writeback.c | 19 +++++++++++++++----
3 files changed, 49 insertions(+), 11 deletions(-)
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>
@@ -34,7 +35,6 @@ enum bdi_stat_item {
#ifdef CONFIG_SMP
struct bdi_per_cpu_data {
- s8 stat_threshold;
s8 bdi_stat_diff[NR_BDI_STAT_ITEMS];
} ____cacheline_aligned_in_smp;
#endif
@@ -60,6 +60,7 @@ struct backing_dev_info {
atomic_long_t bdi_stats[NR_BDI_STAT_ITEMS];
#ifdef CONFIG_SMP
+ int stat_threshold;
struct bdi_per_cpu_data pcd[NR_CPUS];
#endif
};
@@ -109,6 +110,8 @@ static inline unsigned long bdi_stat(str
}
#ifdef CONFIG_SMP
+unsigned long bdi_stat_accurate(struct backing_dev_info *bdi, enum bdi_stat_item item);
+
void __mod_bdi_stat(struct backing_dev_info *bdi, enum bdi_stat_item item, int delta);
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);
@@ -117,8 +120,14 @@ 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);
+static inline unsigned long bdi_stat_delta(struct backing_dev_info *bdi)
+{
+ return num_online_cpus() * bdi->stat_threshold;
+}
#else /* CONFIG_SMP */
+#define bdi_stat_accurate bdi_stat
+
static inline void __mod_bdi_stat(struct backing_dev_info *bdi,
enum bdi_stat_item item, int delta)
{
@@ -142,6 +151,8 @@ 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_stat_delta(bdi) 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
@@ -98,17 +98,33 @@ void bdi_stat_init(struct backing_dev_in
atomic_long_set(&bdi->bdi_stats[i], 0);
#ifdef CONFIG_SMP
+ bdi->stat_threshold = 8 * ilog2(num_online_cpus());
for (i = 0; i < NR_CPUS; i++) {
int j;
for (j = 0; j < NR_BDI_STAT_ITEMS; j++)
bdi->pcd[i].bdi_stat_diff[j] = 0;
- bdi->pcd[i].stat_threshold = 8 * ilog2(num_online_cpus());
}
#endif
}
EXPORT_SYMBOL(bdi_stat_init);
#ifdef CONFIG_SMP
+unsigned long bdi_stat_accurate(struct backing_dev_info *bdi,
+ enum bdi_stat_item item)
+{
+ unsigned long x = __bdi_stat(bdi, item);
+ int cpu;
+
+ for_each_possible_cpu(cpu) {
+ struct bdi_per_cpu_data *pcd = &bdi->pcd[cpu];
+ s8 *p = pcd->bdi_stat_diff + item;
+
+ x += *p;
+ }
+
+ return x;
+}
+
void __mod_bdi_stat(struct backing_dev_info *bdi,
enum bdi_stat_item item, int delta)
{
@@ -118,7 +134,7 @@ void __mod_bdi_stat(struct backing_dev_i
x = delta + *p;
- if (unlikely(x > pcd->stat_threshold || x < -pcd->stat_threshold)) {
+ if (unlikely(x > bdi->stat_threshold || x < -bdi->stat_threshold)) {
bdi_stat_add(x, bdi, item);
x = 0;
}
@@ -144,8 +160,8 @@ void __inc_bdi_stat(struct backing_dev_i
(*p)++;
- if (unlikely(*p > pcd->stat_threshold)) {
- int overstep = pcd->stat_threshold / 2;
+ if (unlikely(*p > bdi->stat_threshold)) {
+ int overstep = bdi->stat_threshold / 2;
bdi_stat_add(*p + overstep, bdi, item);
*p = -overstep;
@@ -170,8 +186,8 @@ void __dec_bdi_stat(struct backing_dev_i
(*p)--;
- if (unlikely(*p < -pcd->stat_threshold)) {
- int overstep = pcd->stat_threshold / 2;
+ if (unlikely(*p < -bdi->stat_threshold)) {
+ int overstep = bdi->stat_threshold / 2;
bdi_stat_add(*p - overstep, bdi, item);
*p = overstep;
Index: linux-2.6/mm/page-writeback.c
===================================================================
--- linux-2.6.orig/mm/page-writeback.c
+++ linux-2.6/mm/page-writeback.c
@@ -341,14 +341,25 @@ static void balance_dirty_pages(struct a
* been flushed to permanent storage.
*/
if (bdi_nr_reclaimable) {
+ unsigned long bdi_nr_writeback;
writeback_inodes(&wbc);
get_dirty_limits(&background_thresh, &dirty_thresh,
&bdi_thresh, bdi);
- bdi_nr_reclaimable = bdi_stat(bdi, BDI_DIRTY) +
- bdi_stat(bdi, BDI_UNSTABLE);
- if (bdi_nr_reclaimable + bdi_stat(bdi, BDI_WRITEBACK) <=
- bdi_thresh)
+
+ if (bdi_thresh < bdi_stat_delta(bdi)) {
+ bdi_nr_reclaimable =
+ bdi_stat_accurate(bdi, BDI_DIRTY) +
+ bdi_stat_accurate(bdi, BDI_UNSTABLE);
+ bdi_nr_writeback =
+ bdi_stat_accurate(bdi, NR_WRITEBACK);
+ } else {
+ bdi_nr_reclaimable = bdi_stat(bdi, BDI_DIRTY) +
+ bdi_stat(bdi, BDI_UNSTABLE);
+ bdi_nr_writeback = bdi_stat(bdi, NR_WRITEBACK);
+ }
+
+ if (bdi_nr_reclaimable + bdi_nr_writeback <= bdi_thresh)
break;
pages_written += write_chunk - wbc.nr_to_write;
-
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