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;