[PATCH] memcg: provide reclaim stats via 'memory.reclaim'

Vaibhav Jain
2022-05-18T22:38:15Z

[1] Provides a way for user-space to trigger proactive reclaim by introducing
a write-only memcg file 'memory.reclaim'. However reclaim stats like number
of pages scanned and reclaimed is still not directly available to the
user-space.

This patch proposes to extend [1] to make the memcg file 'memory.reclaim'
readable which returns the number of pages scanned / reclaimed during the
reclaim process from 'struct vmpressure' associated with each memcg. This should
let user-space asses how successful proactive reclaim triggered from memcg
'memory.reclaim' was ?

With the patch following command flow is expected:

# echo "1M" > memory.reclaim

# cat memory.reclaim
scanned 76
reclaimed 32

[1]: https://lore.kernel.org/r/20220425190040.2475377-1-yosryahmed@google.com

Cc: Shakeel Butt <shakeelb@google.com>
Cc: Yosry Ahmed <yosryahmed@google.com>
Signed-off-by: Vaibhav Jain <vaibhav@linux.ibm.com>
---
Documentation/admin-guide/cgroup-v2.rst | 15 ++++++++++++---
mm/memcontrol.c | 14 ++++++++++++++
2 files changed, 26 insertions(+), 3 deletions(-)

diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst
index 27ebef2485a3..44610165261d 100644
--- a/Documentation/admin-guide/cgroup-v2.rst
+++ b/Documentation/admin-guide/cgroup-v2.rst
@@ -1209,18 +1209,27 @@ PAGE_SIZE multiple when read back.
utility is limited to providing the final safety net.

memory.reclaim
- A write-only nested-keyed file which exists for all cgroups.
+ A nested-keyed file which exists for all cgroups.

- This is a simple interface to trigger memory reclaim in the
- target cgroup.
+ This is a simple interface to trigger memory reclaim and retrieve
+ reclaim stats in the target cgroup.

This file accepts a single key, the number of bytes to reclaim.
No nested keys are currently supported.

+ Reading the file returns number of pages scanned and number of
+ pages reclaimed from the memcg. This information fetched from
+ vmpressure info associated with each cgroup.
+
Example::

echo "1G" > memory.reclaim

+ cat memory.reclaim
+
+ scanned 78
+ reclaimed 30
+
The interface can be later extended with nested keys to
configure the reclaim behavior. For example, specify the
type of memory to reclaim from (anon, file, ..).
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 2e2bfbed4717..9e43580a8726 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -6423,6 +6423,19 @@ static ssize_t memory_oom_group_write(struct kernfs_open_file *of,
return nbytes;
}

+static int memory_reclaim_show(struct seq_file *m, void *v)
+{
+ struct mem_cgroup *memcg = mem_cgroup_from_seq(m);
+ struct vmpressure *vmpr = memcg_to_vmpressure(memcg);
+
+ spin_lock(&vmpr->sr_lock);
+ seq_printf(m, "scanned %lu\nreclaimed %lu\n",
+ vmpr->scanned, vmpr->reclaimed);
+ spin_unlock(&vmpr->sr_lock);
+
+ return 0;
+}
+
static ssize_t memory_reclaim(struct kernfs_open_file *of, char *buf,
size_t nbytes, loff_t off)
{
@@ -6525,6 +6538,7 @@ static struct cftype memory_files[] = {
.name = "reclaim",
.flags = CFTYPE_NS_DELEGATABLE,
.write = memory_reclaim,
+ .seq_show = memory_reclaim_show,
},
{ } /* terminate */
};
--
2.35.1