Commit 77cd8148 authored by Uros Bizjak's avatar Uros Bizjak Committed by Andrew Morton
Browse files

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: default avatarUros Bizjak <ubizjak@gmail.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 91e79d22

mm/vmstat.c

+10 −8
Original line number Diff line number Diff line
@@ -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);