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mm/vmstat: use this_cpu_try_cmpxchg in mod_{zone,node}_state

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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@gmail.com
Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Uros Bizjak 2023-09-04 17:08:49 +02:00 committed by Andrew Morton
parent 91e79d22be
commit 77cd814835
1 changed files with 10 additions and 8 deletions
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18
mm/vmstat.c
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@ -559,8 +559,10 @@ static inline void mod_zone_state(struct zone *zone,
{
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 zone *zone,
*/
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 zone *zone,
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 pglist_data *pgdat,
{
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 pglist_data *pgdat,
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 pglist_data *pgdat,
*/
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 pglist_data *pgdat,
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);