[PATCH v2 3/3] cgroup/dmem: allow max to be set below current usage

[Thadeu Lima de Souza Cascardo <cascardo@igalia.com>]

page_counter_set_max may return -EBUSY in case the current usage is above
the new max. When writing to dmem.max, this error is ignored and the new
max is not set.

Instead of using page_counter_set_max when writing to dmem.max, atomically
update its value irrespective of the current usage.

Since there is no current mechanism to evict a given dmemcg pool, this will
at least prevent the current usage from growing any further.

Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@igalia.com>
---
 kernel/cgroup/dmem.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/cgroup/dmem.c b/kernel/cgroup/dmem.c
index 695d2b7516081256da030c80b54ec1c5fcd6ca16..bf9e0d11e46156a437196c77fdfde84250e65420 100644
--- a/kernel/cgroup/dmem.c
+++ b/kernel/cgroup/dmem.c
@@ -159,7 +159,7 @@ set_resource_low(struct dmem_cgroup_pool_state *pool, u64 val)
 static void
 set_resource_max(struct dmem_cgroup_pool_state *pool, u64 val)
 {
-	page_counter_set_max(&pool->cnt, val);
+	xchg(&pool->cnt.max, val);
 }
 
 static u64 get_resource_low(struct dmem_cgroup_pool_state *pool)

-- 
2.47.3