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Subject: Re: [PATCH] mm/vmstat: don't do count if no needs
Cc:     Andrew Morton <akpm@linux-foundation.org>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
References: <20200720052348.428564-1-alex.shi@linux.alibaba.com>
From:   Alex Shi <alex.shi@linux.alibaba.com>
Message-ID: <1ef9baa0-9788-5917-2590-a8c3fc593b81@linux.alibaba.com>
Date:   Mon, 20 Jul 2020 13:42:45 +0800
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From 4cb977d34227e4bafa95b8da5e47dbd8b6141d26 Mon Sep 17 00:00:00 2001
From: Alex Shi <alex.shi@linux.alibaba.com>
Date: Mon, 20 Jul 2020 11:50:12 +0800
Subject: [PATCH v2] mm/vmstat: don't do count if no needs

For couple of vmstat account funcs, the caller usually doesn't check the
delta value, if delta == 0, irq or atomic operator is a waste. That's
better to be skipped, also add unlikey() since !delta is less happened.

Signed-off-by: Alex Shi <alex.shi@linux.alibaba.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: linux-mm@kvack.org
Cc: linux-kernel@vger.kernel.org
---
 mm/vmstat.c | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

diff --git a/mm/vmstat.c b/mm/vmstat.c
index 3fb23a21f6dd..b02d99dff443 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -321,6 +321,9 @@ void __mod_zone_page_state(struct zone *zone, enum zone_stat_item item,
 	long x;
 	long t;
 
+	if (unlikely(!delta))
+		return;
+
 	x = delta + __this_cpu_read(*p);
 
 	t = __this_cpu_read(pcp->stat_threshold);
@@ -341,6 +344,9 @@ void __mod_node_page_state(struct pglist_data *pgdat, enum node_stat_item item,
 	long x;
 	long t;
 
+	if (unlikely(!delta))
+		return;
+
 	x = delta + __this_cpu_read(*p);
 
 	t = __this_cpu_read(pcp->stat_threshold);
@@ -484,6 +490,9 @@ static inline void mod_zone_state(struct zone *zone,
 	s8 __percpu *p = pcp->vm_stat_diff + item;
 	long o, n, t, z;
 
+	if (unlikely(!delta))
+		return;
+
 	do {
 		z = 0;  /* overflow to zone counters */
 
@@ -518,6 +527,9 @@ static inline void mod_zone_state(struct zone *zone,
 void mod_zone_page_state(struct zone *zone, enum zone_stat_item item,
 			 long delta)
 {
+	if (unlikely(!delta))
+		return;
+
 	mod_zone_state(zone, item, delta, 0);
 }
 EXPORT_SYMBOL(mod_zone_page_state);
@@ -541,6 +553,9 @@ static inline void mod_node_state(struct pglist_data *pgdat,
 	s8 __percpu *p = pcp->vm_node_stat_diff + item;
 	long o, n, t, z;
 
+	if (unlikely(!delta))
+		return;
+
 	do {
 		z = 0;  /* overflow to node counters */
 
@@ -604,6 +619,9 @@ void mod_zone_page_state(struct zone *zone, enum zone_stat_item item,
 {
 	unsigned long flags;
 
+	if (unlikely(!delta))
+		return;
+
 	local_irq_save(flags);
 	__mod_zone_page_state(zone, item, delta);
 	local_irq_restore(flags);
@@ -647,6 +665,9 @@ void mod_node_page_state(struct pglist_data *pgdat, enum node_stat_item item,
 {
 	unsigned long flags;
 
+	if (unlikely(!delta))
+		return;
+
 	local_irq_save(flags);
 	__mod_node_page_state(pgdat, item, delta);
 	local_irq_restore(flags);
-- 
2.18.4