From 77cd814835df22e177a9caac1b046f7ffdfeedd0 Mon Sep 17 00:00:00 2001 From: Uros Bizjak Date: Mon, 4 Sep 2023 17:08:49 +0200 Subject: mm/vmstat: use this_cpu_try_cmpxchg in mod_{zone,node}_state 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 Signed-off-by: Andrew Morton --- mm/vmstat.c | 18 ++++++++++-------- 1 file changed, 10 insertions(+), 8 deletions(-) diff --git a/mm/vmstat.c b/mm/vmstat.c index 00e81e99c6ee..894e4c88d241 100644 --- a/mm/vmstat.c +++ b/mm/vmstat.c @@ -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); -- cgit