The patch titled
Subject: mm/vmstat: use this_cpu_try_cmpxchg in mod_{zone,node}_state
has been added to the -mm mm-unstable branch. Its filename is
mm-vmstat-use-this_cpu_try_cmpxchg-in-mod_zonenode_state.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-vmstat-use-this_cpu_try_cmpxchg-in-mod_zonenode_state.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Uros Bizjak <ubizjak@xxxxxxxxx>
Subject: mm/vmstat: use this_cpu_try_cmpxchg in mod_{zone,node}_state
Date: Mon, 4 Sep 2023 17:08:49 +0200
Use this_cpu_try_cmpxchg instead of this_cpu_cmpxchg (*ptr, old, new) ==
old in mod_zone_state and mod_node_state. x86 CMPXCHG instruction returns
success in ZF flag, so this change saves a compare after cmpxchg (and
related move instruction in front of cmpxchg).
Also, try_cmpxchg implicitly assigns old *ptr value to "old" when cmpxchg
fails. There is no need to re-read the value in the loop.
No functional change intended.
Link: https://lkml.kernel.org/r/20230904150917.8318-1-ubizjak@xxxxxxxxx
Signed-off-by: Uros Bizjak <ubizjak@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/vmstat.c | 18 ++++++++++--------
1 file changed, 10 insertions(+), 8 deletions(-)
--- a/mm/vmstat.c~mm-vmstat-use-this_cpu_try_cmpxchg-in-mod_zonenode_state
+++ a/mm/vmstat.c
@@ -559,8 +559,10 @@ static inline void mod_zone_state(struct
{
struct per_cpu_zonestat __percpu *pcp = zone->per_cpu_zonestats;
s8 __percpu *p = pcp->vm_stat_diff + item;
- long o, n, t, z;
+ long n, t, z;
+ s8 o;
+ o = this_cpu_read(*p);
do {
z = 0; /* overflow to zone counters */
@@ -576,8 +578,7 @@ static inline void mod_zone_state(struct
*/
t = this_cpu_read(pcp->stat_threshold);
- o = this_cpu_read(*p);
- n = delta + o;
+ n = delta + (long)o;
if (abs(n) > t) {
int os = overstep_mode * (t >> 1) ;
@@ -586,7 +587,7 @@ static inline void mod_zone_state(struct
z = n + os;
n = -os;
}
- } while (this_cpu_cmpxchg(*p, o, n) != o);
+ } while (!this_cpu_try_cmpxchg(*p, &o, n));
if (z)
zone_page_state_add(z, zone, item);
@@ -616,7 +617,8 @@ static inline void mod_node_state(struct
{
struct per_cpu_nodestat __percpu *pcp = pgdat->per_cpu_nodestats;
s8 __percpu *p = pcp->vm_node_stat_diff + item;
- long o, n, t, z;
+ long n, t, z;
+ s8 o;
if (vmstat_item_in_bytes(item)) {
/*
@@ -629,6 +631,7 @@ static inline void mod_node_state(struct
delta >>= PAGE_SHIFT;
}
+ o = this_cpu_read(*p);
do {
z = 0; /* overflow to node counters */
@@ -644,8 +647,7 @@ static inline void mod_node_state(struct
*/
t = this_cpu_read(pcp->stat_threshold);
- o = this_cpu_read(*p);
- n = delta + o;
+ n = delta + (long)o;
if (abs(n) > t) {
int os = overstep_mode * (t >> 1) ;
@@ -654,7 +656,7 @@ static inline void mod_node_state(struct
z = n + os;
n = -os;
}
- } while (this_cpu_cmpxchg(*p, o, n) != o);
+ } while (!this_cpu_try_cmpxchg(*p, &o, n));
if (z)
node_page_state_add(z, pgdat, item);
_
Patches currently in -mm which might be from ubizjak@xxxxxxxxx are
mm-vmstat-use-this_cpu_try_cmpxchg-in-mod_zonenode_state.patch
panic-use-atomic_try_cmpxchg-in-panic-and-nmi_panic.patch
