Subject: + vmstat-create-separate-function-to-fold-per-cpu-diffs-into-local-counters.patch added to -mm tree
To: cl@xxxxxxxxx,adobriyan@xxxxxxxxx,js1304@xxxxxxxxx,kosaki.motohiro@xxxxxxxxxxxxxx,tj@xxxxxxxxxx
From: akpm@xxxxxxxxxxxxxxxxxxxx
Date: Wed, 07 Aug 2013 13:43:06 -0700
The patch titled
Subject: vmstat: create separate function to fold per cpu diffs into local counters
has been added to the -mm tree. Its filename is
vmstat-create-separate-function-to-fold-per-cpu-diffs-into-local-counters.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/vmstat-create-separate-function-to-fold-per-cpu-diffs-into-local-counters.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/vmstat-create-separate-function-to-fold-per-cpu-diffs-into-local-counters.patch
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------------------------------------------------------
From: Christoph Lameter <cl@xxxxxxxxx>
Subject: vmstat: create separate function to fold per cpu diffs into local counters
The main idea behind this patchset is to reduce the vmstat update overhead
by avoiding interrupt enable/disable and the use of per cpu atomics.
This patch (of 3):
It is better to have a separate folding function because
refresh_cpu_vm_stats() also does other things like expire pages in the
page allocator caches.
If we have a separate function then refresh_cpu_vm_stats() is only called
from the local cpu which allows additional optimizations.
The folding function is only called when a cpu is being downed and
therefore no other processor will be accessing the counters. Also
simplifies synchronization.
Signed-off-by: Christoph Lameter <cl@xxxxxxxxx>
Cc: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>
CC: Tejun Heo <tj@xxxxxxxxxx>
Cc: Joonsoo Kim <js1304@xxxxxxxxx>
Cc: Alexey Dobriyan <adobriyan@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/vmstat.h | 2 -
mm/page_alloc.c | 2 -
mm/vmstat.c | 40 +++++++++++++++++++++++++++++++++------
3 files changed, 36 insertions(+), 8 deletions(-)
diff -puN include/linux/vmstat.h~vmstat-create-separate-function-to-fold-per-cpu-diffs-into-local-counters include/linux/vmstat.h
--- a/include/linux/vmstat.h~vmstat-create-separate-function-to-fold-per-cpu-diffs-into-local-counters
+++ a/include/linux/vmstat.h
@@ -198,7 +198,7 @@ extern void __inc_zone_state(struct zone
extern void dec_zone_state(struct zone *, enum zone_stat_item);
extern void __dec_zone_state(struct zone *, enum zone_stat_item);
-void refresh_cpu_vm_stats(int);
+void cpu_vm_stats_fold(int);
void refresh_zone_stat_thresholds(void);
void drain_zonestat(struct zone *zone, struct per_cpu_pageset *);
diff -puN mm/page_alloc.c~vmstat-create-separate-function-to-fold-per-cpu-diffs-into-local-counters mm/page_alloc.c
--- a/mm/page_alloc.c~vmstat-create-separate-function-to-fold-per-cpu-diffs-into-local-counters
+++ a/mm/page_alloc.c
@@ -5404,7 +5404,7 @@ static int page_alloc_cpu_notify(struct
* This is only okay since the processor is dead and cannot
* race with what we are doing.
*/
- refresh_cpu_vm_stats(cpu);
+ cpu_vm_stats_fold(cpu);
}
return NOTIFY_OK;
}
diff -puN mm/vmstat.c~vmstat-create-separate-function-to-fold-per-cpu-diffs-into-local-counters mm/vmstat.c
--- a/mm/vmstat.c~vmstat-create-separate-function-to-fold-per-cpu-diffs-into-local-counters
+++ a/mm/vmstat.c
@@ -415,11 +415,7 @@ EXPORT_SYMBOL(dec_zone_page_state);
#endif
/*
- * Update the zone counters for one cpu.
- *
- * The cpu specified must be either the current cpu or a processor that
- * is not online. If it is the current cpu then the execution thread must
- * be pinned to the current cpu.
+ * Update the zone counters for the current cpu.
*
* Note that refresh_cpu_vm_stats strives to only access
* node local memory. The per cpu pagesets on remote zones are placed
@@ -432,7 +428,7 @@ EXPORT_SYMBOL(dec_zone_page_state);
* with the global counters. These could cause remote node cache line
* bouncing and will have to be only done when necessary.
*/
-void refresh_cpu_vm_stats(int cpu)
+static void refresh_cpu_vm_stats(int cpu)
{
struct zone *zone;
int i;
@@ -489,6 +485,38 @@ void refresh_cpu_vm_stats(int cpu)
}
for (i = 0; i < NR_VM_ZONE_STAT_ITEMS; i++)
+ if (global_diff[i])
+ atomic_long_add(global_diff[i], &vm_stat[i]);
+}
+
+/*
+ * Fold the data for an offline cpu into the global array.
+ * There cannot be any access by the offline cpu and therefore
+ * synchronization is simplified.
+ */
+void cpu_vm_stats_fold(int cpu)
+{
+ struct zone *zone;
+ int i;
+ int global_diff[NR_VM_ZONE_STAT_ITEMS] = { 0, };
+
+ for_each_populated_zone(zone) {
+ struct per_cpu_pageset *p;
+
+ p = per_cpu_ptr(zone->pageset, cpu);
+
+ for (i = 0; i < NR_VM_ZONE_STAT_ITEMS; i++)
+ if (p->vm_stat_diff[i]) {
+ int v;
+
+ v = p->vm_stat_diff[i];
+ p->vm_stat_diff[i] = 0;
+ atomic_long_add(v, &zone->vm_stat[i]);
+ global_diff[i] += v;
+ }
+ }
+
+ for (i = 0; i < NR_VM_ZONE_STAT_ITEMS; i++)
if (global_diff[i])
atomic_long_add(global_diff[i], &vm_stat[i]);
}
_
Patches currently in -mm which might be from cl@xxxxxxxxx are
vmstat-create-separate-function-to-fold-per-cpu-diffs-into-local-counters.patch
vmstat-create-fold_diff.patch
vmstat-use-this_cpu-to-avoid-irqon-off-sequence-in-refresh_cpu_vm_stats.patch
linux-next.patch
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