[PATCH v7 10/13] mm/vmstat: use xchg in cpu_vm_stats_fold

Marcelo Tosatti
2023-03-20T18:20:27Z

In preparation to switch vmstat shepherd to flush
per-CPU counters remotely, use xchg instead of a
pair of read/write instructions.

Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

---

Index: linux-vmstat-remote/mm/vmstat.c
===================================================================
--- linux-vmstat-remote.orig/mm/vmstat.c
+++ linux-vmstat-remote/mm/vmstat.c
@@ -924,7 +924,7 @@ static int refresh_cpu_vm_stats(bool do_
}

/*
- * Fold the data for an offline cpu into the global array.
+ * Fold the data for a cpu into the global array.
* There cannot be any access by the offline cpu and therefore
* synchronization is simplified.
*/
@@ -945,8 +945,7 @@ void cpu_vm_stats_fold(int cpu)
if (pzstats->vm_stat_diff[i]) {
int v;

- v = pzstats->vm_stat_diff[i];
- pzstats->vm_stat_diff[i] = 0;
+ v = xchg(&pzstats->vm_stat_diff[i], 0);
atomic_long_add(v, &zone->vm_stat[i]);
global_zone_diff[i] += v;
}
@@ -956,8 +955,7 @@ void cpu_vm_stats_fold(int cpu)
if (pzstats->vm_numa_event[i]) {
unsigned long v;

- v = pzstats->vm_numa_event[i];
- pzstats->vm_numa_event[i] = 0;
+ v = xchg(&pzstats->vm_numa_event[i], 0);
zone_numa_event_add(v, zone, i);
}
}
@@ -973,8 +971,7 @@ void cpu_vm_stats_fold(int cpu)
if (p->vm_node_stat_diff[i]) {
int v;

- v = p->vm_node_stat_diff[i];
- p->vm_node_stat_diff[i] = 0;
+ v = xchg(&p->vm_node_stat_diff[i], 0);
atomic_long_add(v, &pgdat->vm_stat[i]);
global_node_diff[i] += v;
}