On 10/11/22 11:39, Michal Hocko wrote:
On Tue 11-10-22 10:30:15, Waiman Long wrote:
Since commit bc50bcc6e00b ("mm: memcontrol: clean up and document
effective low/min calculations"), the effective low/min protections can
be non-zero even if the corresponding memory.low/min values are 0. That
can surprise users to see MEMCG_LOW events even when the memory.low
value is not set. One example is the LTP's memcontrol04 test which fails
because it detects some MEMCG_LOW events for a cgroup with a memory.min
value of 0.
Is this with memory_recursiveprot mount option?
Yes, the memory_recursiveprot mount option is indeed turned on.
Fix this by updating effective_protection() to not returning a non-zero
low/min protection values if the corresponding memory.low/min values
or those of its parent are 0.
Fixes: bc50bcc6e00b ("mm: memcontrol: clean up and document effective low/min calculations")
Signed-off-by: Waiman Long <longman@xxxxxxxxxx>
---
mm/memcontrol.c | 3 +++
1 file changed, 3 insertions(+)
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index b69979c9ced5..893d4d5e518a 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -6660,6 +6660,9 @@ static unsigned long effective_protection(unsigned long usage,
unsigned long protected;
unsigned long ep;
+ if (!setting || !parent_effective)
+ return 0UL; /* No protection is needed */
+
This will break the above memory_recursiveprot AFAICS.
You are right about that. An alternative way to address this issue is to
disable memory low event when memory.low isn't set. An user who want to
track memory.low event has to set it to a non-zero value. Would that be
acceptable?
Cheers,
Longman
