diff options
| -rw-r--r-- | mm/memcontrol.c | 50 |
1 files changed, 32 insertions, 18 deletions
diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 425aa0caa712..a6eef3603b72 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -5317,38 +5317,52 @@ struct cgroup_subsys memory_cgrp_subsys = { /** * mem_cgroup_low - check if memory consumption is below the normal range - * @root: the highest ancestor to consider + * @root: the top ancestor of the sub-tree being checked * @memcg: the memory cgroup to check * * Returns %true if memory consumption of @memcg, and that of all - * configurable ancestors up to @root, is below the normal range. + * ancestors up to (but not including) @root, is below the normal range. + * + * @root is exclusive; it is never low when looked at directly and isn't + * checked when traversing the hierarchy. + * + * Excluding @root enables using memory.low to prioritize memory usage + * between cgroups within a subtree of the hierarchy that is limited by + * memory.high or memory.max. + * + * For example, given cgroup A with children B and C: + * + * A + * / \ + * B C + * + * and + * + * 1. A/memory.current > A/memory.high + * 2. A/B/memory.current < A/B/memory.low + * 3. A/C/memory.current >= A/C/memory.low + * + * As 'A' is high, i.e. triggers reclaim from 'A', and 'B' is low, we + * should reclaim from 'C' until 'A' is no longer high or until we can + * no longer reclaim from 'C'. If 'A', i.e. @root, isn't excluded by + * mem_cgroup_low when reclaming from 'A', then 'B' won't be considered + * low and we will reclaim indiscriminately from both 'B' and 'C'. */ bool mem_cgroup_low(struct mem_cgroup *root, struct mem_cgroup *memcg) { if (mem_cgroup_disabled()) return false; - /* - * The toplevel group doesn't have a configurable range, so - * it's never low when looked at directly, and it is not - * considered an ancestor when assessing the hierarchy. - */ - - if (memcg == root_mem_cgroup) - return false; - - if (page_counter_read(&memcg->memory) >= memcg->low) + if (!root) + root = root_mem_cgroup; + if (memcg == root) return false; - while (memcg != root) { - memcg = parent_mem_cgroup(memcg); - - if (memcg == root_mem_cgroup) - break; - + for (; memcg != root; memcg = parent_mem_cgroup(memcg)) { if (page_counter_read(&memcg->memory) >= memcg->low) return false; } + return true; } |