[patch 2/3] mm: memcontrol: simplify detecting when the memory+swap limit is hit

Johannes Weiner
2014-09-24T15:08:57Z

When attempting to charge pages, we first charge the memory counter
and then the memory+swap counter. If one of the counters is at its
limit, we enter reclaim, but if it's the memory+swap counter, reclaim
shouldn't swap because that wouldn't change the situation. However,
if the counters have the same limits, we never get to the memory+swap
limit. To know whether reclaim should swap or not, there is a state
flag that indicates whether the limits are equal and whether hitting
the memory limit implies hitting the memory+swap limit.

Just try the memory+swap counter first.

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
---
mm/memcontrol.c | 47 +++++++++++++----------------------------------
1 file changed, 13 insertions(+), 34 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 1ec22bf380d0..89c920156c2a 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -315,9 +315,6 @@ struct mem_cgroup {
/* OOM-Killer disable */
int oom_kill_disable;

- /* set when res.limit == memsw.limit */
- bool memsw_is_minimum;
-
/* protect arrays of thresholds */
struct mutex thresholds_lock;

@@ -1804,8 +1801,6 @@ static unsigned long mem_cgroup_reclaim(struct mem_cgroup *memcg,

if (flags & MEM_CGROUP_RECLAIM_NOSWAP)
noswap = true;
- if (!(flags & MEM_CGROUP_RECLAIM_SHRINK) && memcg->memsw_is_minimum)
- noswap = true;

for (loop = 0; loop < MEM_CGROUP_MAX_RECLAIM_LOOPS; loop++) {
if (loop)
@@ -2543,16 +2538,17 @@ retry:
goto done;

size = batch * PAGE_SIZE;
- if (!res_counter_charge(&memcg->res, size, &fail_res)) {
- if (!do_swap_account)
+ if (!do_swap_account ||
+ !res_counter_charge(&memcg->memsw, size, &fail_res)) {
+ if (!res_counter_charge(&memcg->res, size, &fail_res))
goto done_restock;
- if (!res_counter_charge(&memcg->memsw, size, &fail_res))
- goto done_restock;
- res_counter_uncharge(&memcg->res, size);
+ if (do_swap_account)
+ res_counter_uncharge(&memcg->memsw, size);
+ mem_over_limit = mem_cgroup_from_res_counter(fail_res, res);
+ } else {
mem_over_limit = mem_cgroup_from_res_counter(fail_res, memsw);
flags |= MEM_CGROUP_RECLAIM_NOSWAP;
- } else
- mem_over_limit = mem_cgroup_from_res_counter(fail_res, res);
+ }

if (batch > nr_pages) {
batch = nr_pages;
@@ -3615,7 +3611,6 @@ static int mem_cgroup_resize_limit(struct mem_cgroup *memcg,
unsigned long long val)
{
int retry_count;
- u64 memswlimit, memlimit;
int ret = 0;
int children = mem_cgroup_count_children(memcg);
u64 curusage, oldusage;
@@ -3642,24 +3637,16 @@ static int mem_cgroup_resize_limit(struct mem_cgroup *memcg,
* We have to guarantee memcg->res.limit <= memcg->memsw.limit.
*/
mutex_lock(&set_limit_mutex);
- memswlimit = res_counter_read_u64(&memcg->memsw, RES_LIMIT);
- if (memswlimit < val) {
+ if (res_counter_read_u64(&memcg->memsw, RES_LIMIT) < val) {
ret = -EINVAL;
mutex_unlock(&set_limit_mutex);
break;
}

- memlimit = res_counter_read_u64(&memcg->res, RES_LIMIT);
- if (memlimit < val)
+ if (res_counter_read_u64(&memcg->res, RES_LIMIT) < val)
enlarge = 1;

ret = res_counter_set_limit(&memcg->res, val);
- if (!ret) {
- if (memswlimit == val)
- memcg->memsw_is_minimum = true;
- else
- memcg->memsw_is_minimum = false;
- }
mutex_unlock(&set_limit_mutex);

if (!ret)
@@ -3684,7 +3671,7 @@ static int mem_cgroup_resize_memsw_limit(struct mem_cgroup *memcg,
unsigned long long val)
{
int retry_count;
- u64 memlimit, memswlimit, oldusage, curusage;
+ u64 oldusage, curusage;
int children = mem_cgroup_count_children(memcg);
int ret = -EBUSY;
int enlarge = 0;
@@ -3703,22 +3690,14 @@ static int mem_cgroup_resize_memsw_limit(struct mem_cgroup *memcg,
* We have to guarantee memcg->res.limit <= memcg->memsw.limit.
*/
mutex_lock(&set_limit_mutex);
- memlimit = res_counter_read_u64(&memcg->res, RES_LIMIT);
- if (memlimit > val) {
+ if (res_counter_read_u64(&memcg->res, RES_LIMIT) > val) {
ret = -EINVAL;
mutex_unlock(&set_limit_mutex);
break;
}
- memswlimit = res_counter_read_u64(&memcg->memsw, RES_LIMIT);
- if (memswlimit < val)
+ if (res_counter_read_u64(&memcg->memsw, RES_LIMIT) < val)
enlarge = 1;
ret = res_counter_set_limit(&memcg->memsw, val);
- if (!ret) {
- if (memlimit == val)
- memcg->memsw_is_minimum = true;
- else
- memcg->memsw_is_minimum = false;
- }
mutex_unlock(&set_limit_mutex);

if (!ret)
--
2.1.0