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Subject[PATCH 2/2] mm, memcontrol: Implement memory.swap.events
Date
Add swap max and fail events so that userland can monitor and respond
to running out of swap.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
Cc: Roman Gushchin <guro@fb.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: linux-api@vger.kernel.org
---
Documentation/cgroup-v2.txt | 16 ++++++++++++++++
include/linux/memcontrol.h | 5 +++++
mm/memcontrol.c | 24 +++++++++++++++++++++++-
3 files changed, 44 insertions(+), 1 deletion(-)

diff --git a/Documentation/cgroup-v2.txt b/Documentation/cgroup-v2.txt
index 74cdeae..b0dda10 100644
--- a/Documentation/cgroup-v2.txt
+++ b/Documentation/cgroup-v2.txt
@@ -1199,6 +1199,22 @@ PAGE_SIZE multiple when read back.
Swap usage hard limit. If a cgroup's swap usage reaches this
limit, anonymous memory of the cgroup will not be swapped out.

+ memory.swap.events
+ A read-only flat-keyed file which exists on non-root cgroups.
+ The following entries are defined. Unless specified
+ otherwise, a value change in this file generates a file
+ modified event.
+
+ max
+ The number of times the cgroup's swap usage was about
+ to go over the max boundary and swap allocation
+ failed.
+
+ fail
+ The number of times swap allocation failed either
+ because of running out of swap system-wide or max
+ limit.
+

Usage Guidelines
~~~~~~~~~~~~~~~~
diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 85a8f00..f198339 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -54,6 +54,8 @@ enum memcg_event_item {
MEMCG_HIGH,
MEMCG_MAX,
MEMCG_OOM,
+ MEMCG_SWAP_MAX,
+ MEMCG_SWAP_FAIL,
MEMCG_NR_EVENTS,
};

@@ -202,6 +204,9 @@ struct mem_cgroup {
/* handle for "memory.events" */
struct cgroup_file events_file;

+ /* handle for "memory.swap.events" */
+ struct cgroup_file swap_events_file;
+
/* protect arrays of thresholds */
struct mutex thresholds_lock;

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 9f9c8a7..1a14d4a4 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -5987,13 +5987,17 @@ int mem_cgroup_try_charge_swap(struct page *page, swp_entry_t entry)
if (!memcg)
return 0;

- if (!entry.val)
+ if (!entry.val) {
+ mem_cgroup_event(memcg, MEMCG_SWAP_FAIL);
return 0;
+ }

memcg = mem_cgroup_id_get_online(memcg);

if (!mem_cgroup_is_root(memcg) &&
!page_counter_try_charge(&memcg->swap, nr_pages, &counter)) {
+ mem_cgroup_event(memcg, MEMCG_SWAP_MAX);
+ mem_cgroup_event(memcg, MEMCG_SWAP_FAIL);
mem_cgroup_id_put(memcg);
return -ENOMEM;
}
@@ -6131,6 +6135,18 @@ static ssize_t swap_max_write(struct kernfs_open_file *of,
return nbytes;
}

+static int swap_events_show(struct seq_file *m, void *v)
+{
+ struct mem_cgroup *memcg = mem_cgroup_from_css(seq_css(m));
+
+ memcg_stat_flush(memcg);
+
+ seq_printf(m, "max %llu\n", memcg->events[MEMCG_SWAP_MAX]);
+ seq_printf(m, "fail %llu\n", memcg->events[MEMCG_SWAP_FAIL]);
+
+ return 0;
+}
+
static struct cftype swap_files[] = {
{
.name = "swap.current",
@@ -6143,6 +6159,12 @@ static struct cftype swap_files[] = {
.seq_show = swap_max_show,
.write = swap_max_write,
},
+ {
+ .name = "swap.events",
+ .flags = CFTYPE_NOT_ON_ROOT,
+ .file_offset = offsetof(struct mem_cgroup, swap_events_file),
+ .seq_show = swap_events_show,
+ },
{ } /* terminate */
};

--
2.9.5
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