[PATCH v5 2/2] mm/memcontrol.c: Reduce reclaim retries in mem_cgroup_resize_limit()

Andrey Ryabinin
2018-01-19T13:25:44Z

Currently mem_cgroup_resize_limit() retries to set limit after reclaiming
32 pages. It makes more sense to reclaim needed amount of pages right away.

This works noticeably faster, especially if 'usage - limit' big.
E.g. bringing down limit from 4G to 50M:

Before:
# perf stat echo 50M > memory.limit_in_bytes

Performance counter stats for 'echo 50M':

386.582382 task-clock (msec) # 0.835 CPUs utilized
2,502 context-switches # 0.006 M/sec

0.463244382 seconds time elapsed

After:
# perf stat echo 50M > memory.limit_in_bytes

Performance counter stats for 'echo 50M':

169.403906 task-clock (msec) # 0.849 CPUs utilized
14 context-switches # 0.083 K/sec

0.199536900 seconds time elapsed

Signed-off-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
---
mm/memcontrol.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 9d987f3e79dc..09bac2df2f12 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2448,6 +2448,7 @@ static DEFINE_MUTEX(memcg_limit_mutex);
static int mem_cgroup_resize_limit(struct mem_cgroup *memcg,
unsigned long limit, bool memsw)
{
+ unsigned long nr_pages;
bool enlarge = false;
int ret;
bool limits_invariant;
@@ -2479,8 +2480,9 @@ static int mem_cgroup_resize_limit(struct mem_cgroup *memcg,
if (!ret)
break;

- if (!try_to_free_mem_cgroup_pages(memcg, 1,
- GFP_KERNEL, !memsw)) {
+ nr_pages = max_t(long, 1, page_counter_read(counter) - limit);
+ if (!try_to_free_mem_cgroup_pages(memcg, nr_pages,
+ GFP_KERNEL, !memsw)) {
ret = -EBUSY;
break;
}
--
2.13.6