[PATCH] mm/memcontrol: Add the drop_cache interface for cgroup v2

zangchunxin
2020-09-21T08:02:55Z

From: Chunxin Zang <zangchunxin@bytedance.com>

In the cgroup v1, we have 'force_mepty' interface. This is very
useful for userspace to actively release memory. But the cgroup
v2 does not.

This patch reuse cgroup v1's function, but have a new name for
the interface. Because I think 'drop_cache' may be is easier to
understand :)

Signed-off-by: Chunxin Zang <zangchunxin@bytedance.com>
---
Documentation/admin-guide/cgroup-v2.rst | 11 +++++++++++
mm/memcontrol.c | 5 +++++
2 files changed, 16 insertions(+)

diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst
index ce3e05e41724..fbff959c8116 100644
--- a/Documentation/admin-guide/cgroup-v2.rst
+++ b/Documentation/admin-guide/cgroup-v2.rst
@@ -1181,6 +1181,17 @@ PAGE_SIZE multiple when read back.
high limit is used and monitored properly, this limit's
utility is limited to providing the final safety net.

+ memory.drop_cache
+ A write-only single value file which exists on non-root
+ cgroups.
+
+ Provide a mechanism for users to actively trigger memory
+ reclaim. The cgroup will be reclaimed and as many pages
+ reclaimed as possible.
+
+ It will broke low boundary. Because it tries to reclaim the
+ memory many times, until the memory drops to a certain level.
+
memory.oom.group
A read-write single value file which exists on non-root
cgroups. The default value is "0".
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 0b38b6ad547d..98646484efff 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -6226,6 +6226,11 @@ static struct cftype memory_files[] = {
.write = memory_max_write,
},
{
+ .name = "drop_cache",
+ .flags = CFTYPE_NOT_ON_ROOT,
+ .write = mem_cgroup_force_empty_write,
+ },
+ {
.name = "events",
.flags = CFTYPE_NOT_ON_ROOT,
.file_offset = offsetof(struct mem_cgroup, events_file),
--
2.11.0