The commit is pushed to "branch-rh7-3.10.0-514.6.1.vz7.28.x-ovz" and will
appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh7-3.10.0-514.6.1.vz7.28.6
------>
commit 31166ec0c438e0b8da2e41ba99661791f837e173
Author: Greg Thelen <gthe...@google.com>
Date: Mon Feb 20 14:35:32 2017 +0400
ms/memcg: make mem_cgroup_read_stat() unsigned
commit 484ebb3b8c8b27dd2171696462a3116edb9ff801 upstream.
mem_cgroup_read_stat() returns a page count by summing per cpu page
counters. The summing is racy wrt. updates, so a transient negative
sum is possible. Callers don't want negative values:
- mem_cgroup_wb_stats() doesn't want negative nr_dirty or nr_writeback.
This could confuse dirty throttling.
- oom reports and memory.stat shouldn't show confusing negative usage.
- tree_usage() already avoids negatives.
Avoid returning negative page counts from mem_cgroup_read_stat() and
convert it to unsigned.
[a...@linux-foundation.org: fix old typo while we're in there]
Signed-off-by: Greg Thelen <gthe...@google.com>
Cc: Johannes Weiner <han...@cmpxchg.org>
Acked-by: Michal Hocko <mho...@suse.com>
Cc: <sta...@vger.kernel.org> [4.2+]
Signed-off-by: Andrew Morton <a...@linux-foundation.org>
Signed-off-by: Linus Torvalds <torva...@linux-foundation.org>
https://jira.sw.ru/browse/PSBM-56256
Signed-off-by: Andrey Ryabinin <aryabi...@virtuozzo.com>
---
mm/memcontrol.c | 30 ++++++++++++++++++------------
1 file changed, 18 insertions(+), 12 deletions(-)
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 49b69f7..95b1c0c 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -919,12 +919,14 @@ mem_cgroup_largest_soft_limit_node(struct
mem_cgroup_tree_per_zone *mctz)
}
/*
+ * Return page count for single (non recursive) @memcg.
+ *
* Implementation Note: reading percpu statistics for memcg.
*
* Both of vmstat[] and percpu_counter has threshold and do periodic
* synchronization to implement "quick" read. There are trade-off between
* reading cost and precision of value. Then, we may have a chance to implement
- * a periodic synchronizion of counter in memcg's counter.
+ * a periodic synchronization of counter in memcg's counter.
*
* But this _read() function is used for user interface now. The user accounts
* memory usage by memory cgroup and he _always_ requires exact value because
@@ -934,17 +936,24 @@ mem_cgroup_largest_soft_limit_node(struct
mem_cgroup_tree_per_zone *mctz)
*
* If there are kernel internal actions which can make use of some not-exact
* value, and reading all cpu value can be performance bottleneck in some
- * common workload, threashold and synchonization as vmstat[] should be
+ * common workload, threshold and synchronization as vmstat[] should be
* implemented.
*/
-static long mem_cgroup_read_stat(struct mem_cgroup *memcg,
- enum mem_cgroup_stat_index idx)
+static unsigned long
+mem_cgroup_read_stat(struct mem_cgroup *memcg, enum mem_cgroup_stat_index idx)
{
long val = 0;
int cpu;
+ /* Per-cpu values can be negative, use a signed accumulator */
for_each_possible_cpu(cpu)
val += per_cpu(memcg->stat->count[idx], cpu);
+ /*
+ * Summing races with updates, so val may be negative. Avoid exposing
+ * transient negative values.
+ */
+ if (val < 0)
+ val = 0;
return val;
}
@@ -1961,7 +1970,7 @@ done:
for (i = 0; i < MEM_CGROUP_STAT_NSTATS; i++) {
if (i == MEM_CGROUP_STAT_SWAP && !do_swap_account)
continue;
- pr_cont(" %s:%ldKB", mem_cgroup_stat_names[i],
+ pr_cont(" %s:%luKB", mem_cgroup_stat_names[i],
K(mem_cgroup_read_stat(iter, i)));
}
@@ -4162,14 +4171,11 @@ static unsigned long mem_cgroup_recursive_stat(struct
mem_cgroup *memcg,
enum mem_cgroup_stat_index idx)
{
struct mem_cgroup *iter;
- long val = 0;
+ unsigned long val = 0;
- /* Per-cpu values can be negative, use a signed accumulator */
for_each_mem_cgroup_tree(iter, memcg)
val += mem_cgroup_read_stat(iter, idx);
- if (val < 0) /* race ? */
- val = 0;
return val;
}
@@ -5050,7 +5056,7 @@ static int memcg_stat_show(struct cgroup *cont, struct
cftype *cft,
for (i = 0; i < MEM_CGROUP_STAT_NSTATS; i++) {
if (i == MEM_CGROUP_STAT_SWAP && !do_swap_account)
continue;
- seq_printf(m, "%s %ld\n", mem_cgroup_stat_names[i],
+ seq_printf(m, "%s %lu\n", mem_cgroup_stat_names[i],
mem_cgroup_read_stat(memcg, i) * PAGE_SIZE);
}
@@ -5075,13 +5081,13 @@ static int memcg_stat_show(struct cgroup *cont, struct
cftype *cft,
(u64)memsw * PAGE_SIZE);
for (i = 0; i < MEM_CGROUP_STAT_NSTATS; i++) {
- long long val = 0;
+ unsigned long long val = 0;
if (i == MEM_CGROUP_STAT_SWAP && !do_swap_account)
continue;
for_each_mem_cgroup_tree(mi, memcg)
val += mem_cgroup_read_stat(mi, i) * PAGE_SIZE;
- seq_printf(m, "total_%s %lld\n", mem_cgroup_stat_names[i], val);
+ seq_printf(m, "total_%s %llu\n", mem_cgroup_stat_names[i], val);
}
for (i = 0; i < MEM_CGROUP_EVENTS_NSTATS; i++) {
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