[PATCH] memcg: remove unneeded preempt_disable

Greg Thelen
2011-08-18T06:51:37Z

Both mem_cgroup_charge_statistics() and mem_cgroup_move_account() were
unnecessarily disabling preemption when adjusting per-cpu counters:
preempt_disable()
__this_cpu_xxx()
__this_cpu_yyy()
preempt_enable()

This change does not disable preemption and thus CPU switch is possible
within these routines. This does not cause a problem because the total
of all cpu counters is summed when reporting stats. Now both
mem_cgroup_charge_statistics() and mem_cgroup_move_account() look like:
this_cpu_xxx()
this_cpu_yyy()

Reported-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: Greg Thelen <gthelen@google.com>
---
mm/memcontrol.c | 20 +++++++-------------
1 files changed, 7 insertions(+), 13 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index c6faa32..048b205 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -664,24 +664,20 @@ static unsigned long mem_cgroup_read_events(struct mem_cgroup *mem,
static void mem_cgroup_charge_statistics(struct mem_cgroup *mem,
bool file, int nr_pages)
{
- preempt_disable();
-
if (file)
- __this_cpu_add(mem->stat->count[MEM_CGROUP_STAT_CACHE], nr_pages);
+ this_cpu_add(mem->stat->count[MEM_CGROUP_STAT_CACHE], nr_pages);
else
- __this_cpu_add(mem->stat->count[MEM_CGROUP_STAT_RSS], nr_pages);
+ this_cpu_add(mem->stat->count[MEM_CGROUP_STAT_RSS], nr_pages);

/* pagein of a big page is an event. So, ignore page size */
if (nr_pages > 0)
- __this_cpu_inc(mem->stat->events[MEM_CGROUP_EVENTS_PGPGIN]);
+ this_cpu_inc(mem->stat->events[MEM_CGROUP_EVENTS_PGPGIN]);
else {
- __this_cpu_inc(mem->stat->events[MEM_CGROUP_EVENTS_PGPGOUT]);
+ this_cpu_inc(mem->stat->events[MEM_CGROUP_EVENTS_PGPGOUT]);
nr_pages = -nr_pages; /* for event */
}

- __this_cpu_add(mem->stat->events[MEM_CGROUP_EVENTS_COUNT], nr_pages);
-
- preempt_enable();
+ this_cpu_add(mem->stat->events[MEM_CGROUP_EVENTS_COUNT], nr_pages);
}

unsigned long
@@ -2713,10 +2709,8 @@ static int mem_cgroup_move_account(struct page *page,

if (PageCgroupFileMapped(pc)) {
/* Update mapped_file data for mem_cgroup */
- preempt_disable();
- __this_cpu_dec(from->stat->count[MEM_CGROUP_STAT_FILE_MAPPED]);
- __this_cpu_inc(to->stat->count[MEM_CGROUP_STAT_FILE_MAPPED]);
- preempt_enable();
+ this_cpu_dec(from->stat->count[MEM_CGROUP_STAT_FILE_MAPPED]);
+ this_cpu_inc(to->stat->count[MEM_CGROUP_STAT_FILE_MAPPED]);
}
mem_cgroup_charge_statistics(from, PageCgroupCache(pc), -nr_pages);
if (uncharge)
--
1.7.3.1