On Fri, Apr 24, 2020 at 09:14:52AM -0400, Johannes Weiner wrote:
> However, mem_cgroup_protected() never expected anybody to look at the
> effective protection values when it indicated that the cgroup is above
> its protection. As a result, a query during limit reclaim may return
> stale protection values that were calculated by a previous reclaim
> cycle in which the cgroup did have siblings.
Btw, I think there is opportunity to make this a bit less error prone.
We have a mem_cgroup_protected() that returns yes or no, essentially,
but protection isn't a binary state anymore.
It's also been a bit iffy that it looks like a simple predicate
function, but it indeed needs to run procedurally for each cgroup in
order for the calculations throughout the tree to be correct.
It might be better to have a
mem_cgroup_calculate_protection()
that runs for every cgroup we visit and sets up the internal state;
then have more self-explanatory query functions on top of that:
mem_cgroup_below_min()
mem_cgroup_below_low()
mem_cgroup_protection()
What do you guys think?
diff --git a/mm/vmscan.c b/mm/vmscan.c
index e0f502b5fca6..dbd3f75d39b9 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2615,14 +2615,15 @@ static void shrink_node_memcgs(pg_data_t *pgdat, struct scan_control *sc)
unsigned long reclaimed;
unsigned long scanned;
- switch (mem_cgroup_protected(target_memcg, memcg)) {
- case MEMCG_PROT_MIN:
+ mem_cgroup_calculate_protection(target_memcg, memcg);
+
+ if (mem_cgroup_below_min(memcg)) {
/*
* Hard protection.
* If there is no reclaimable memory, OOM.
*/
continue;
- case MEMCG_PROT_LOW:
+ } else if (mem_cgroup_below_low(memcg)) {
/*
* Soft protection.
* Respect the protection only as long as
@@ -2634,16 +2635,6 @@ static void shrink_node_memcgs(pg_data_t *pgdat, struct scan_control *sc)
continue;
}
memcg_memory_event(memcg, MEMCG_LOW);
- break;
- case MEMCG_PROT_NONE:
- /*
- * All protection thresholds breached. We may
- * still choose to vary the scan pressure
- * applied based on by how much the cgroup in
- * question has exceeded its protection
- * thresholds (see get_scan_count).
- */
- break;
}
reclaimed = sc->nr_reclaimed;
