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-rw-r--r--mm/memcontrol.c50
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;
}