Re: [PATCH] mm/vmstat: don't do count if no needs

[Alex Shi]

>From 4cb977d34227e4bafa95b8da5e47dbd8b6141d26 Mon Sep 17 00:00:00 2001
From: Alex Shi <alex....@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....@linux.alibaba.com>
Cc: Andrew Morton <a...@linux-foundation.org>
Cc: linux...@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