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Message-ID: <20230515180138.668066640@redhat.com>
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Date:   Mon, 15 May 2023 15:00:25 -0300
From:   Marcelo Tosatti <mtosatti@redhat.com>
To:     Christoph Lameter <cl@linux.com>
Cc:     Aaron Tomlin <atomlin@atomlin.com>,
        Frederic Weisbecker <frederic@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        Russell King <linux@armlinux.org.uk>,
        Huacai Chen <chenhuacai@kernel.org>,
        Heiko Carstens <hca@linux.ibm.com>, x86@kernel.org,
        Vlastimil Babka <vbabka@suse.cz>,
        Michal Hocko <mhocko@suse.com>,
        Marcelo Tosatti <mtosatti@redhat.com>
Subject: [PATCH v8 10/13] mm/vmstat: use xchg in cpu_vm_stats_fold
References: <20230515180015.016409657@redhat.com>
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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;
 			}