diff options
Diffstat (limited to 'mm/memcontrol.c')
| -rw-r--r-- | mm/memcontrol.c | 175 |
1 files changed, 83 insertions, 92 deletions
diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 43bd549cf3f5..0e3a8c11fb3b 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -6234,6 +6234,76 @@ struct cgroup_subsys memory_cgrp_subsys = { .early_init = 0, }; +/* + * This function calculates an individual cgroup's effective + * protection which is derived from its own memory.min/low, its + * parent's and siblings' settings, as well as the actual memory + * distribution in the tree. + * + * The following rules apply to the effective protection values: + * + * 1. At the first level of reclaim, effective protection is equal to + * the declared protection in memory.min and memory.low. + * + * 2. To enable safe delegation of the protection configuration, at + * subsequent levels the effective protection is capped to the + * parent's effective protection. + * + * 3. To make complex and dynamic subtrees easier to configure, the + * user is allowed to overcommit the declared protection at a given + * level. If that is the case, the parent's effective protection is + * distributed to the children in proportion to how much protection + * they have declared and how much of it they are utilizing. + * + * This makes distribution proportional, but also work-conserving: + * if one cgroup claims much more protection than it uses memory, + * the unused remainder is available to its siblings. + * + * 4. Conversely, when the declared protection is undercommitted at a + * given level, the distribution of the larger parental protection + * budget is NOT proportional. A cgroup's protection from a sibling + * is capped to its own memory.min/low setting. + * + */ +static unsigned long effective_protection(unsigned long usage, + unsigned long setting, + unsigned long parent_effective, + unsigned long siblings_protected) +{ + unsigned long protected; + + protected = min(usage, setting); + /* + * If all cgroups at this level combined claim and use more + * protection then what the parent affords them, distribute + * shares in proportion to utilization. + * + * We are using actual utilization rather than the statically + * claimed protection in order to be work-conserving: claimed + * but unused protection is available to siblings that would + * otherwise get a smaller chunk than what they claimed. + */ + if (siblings_protected > parent_effective) + return protected * parent_effective / siblings_protected; + + /* + * Ok, utilized protection of all children is within what the + * parent affords them, so we know whatever this child claims + * and utilizes is effectively protected. + * + * If there is unprotected usage beyond this value, reclaim + * will apply pressure in proportion to that amount. + * + * If there is unutilized protection, the cgroup will be fully + * shielded from reclaim, but we do return a smaller value for + * protection than what the group could enjoy in theory. This + * is okay. With the overcommit distribution above, effective + * protection is always dependent on how memory is actually + * consumed among the siblings anyway. + */ + return protected; +} + /** * mem_cgroup_protected - check if memory consumption is in the normal range * @root: the top ancestor of the sub-tree being checked @@ -6247,67 +6317,11 @@ struct cgroup_subsys memory_cgrp_subsys = { * MEMCG_PROT_LOW: cgroup memory is protected as long there is * an unprotected supply of reclaimable memory from other cgroups. * MEMCG_PROT_MIN: cgroup memory is protected - * - * @root is exclusive; it is never protected when looked at directly - * - * To provide a proper hierarchical behavior, effective memory.min/low values - * are used. Below is the description of how effective memory.low is calculated. - * Effective memory.min values is calculated in the same way. - * - * Effective memory.low is always equal or less than the original memory.low. - * If there is no memory.low overcommittment (which is always true for - * top-level memory cgroups), these two values are equal. - * Otherwise, it's a part of parent's effective memory.low, - * calculated as a cgroup's memory.low usage divided by sum of sibling's - * memory.low usages, where memory.low usage is the size of actually - * protected memory. - * - * low_usage - * elow = min( memory.low, parent->elow * ------------------ ), - * siblings_low_usage - * - * low_usage = min(memory.low, memory.current) - * - * - * Such definition of the effective memory.low provides the expected - * hierarchical behavior: parent's memory.low value is limiting - * children, unprotected memory is reclaimed first and cgroups, - * which are not using their guarantee do not affect actual memory - * distribution. - * - * For example, if there are memcgs A, A/B, A/C, A/D and A/E: - * - * A A/memory.low = 2G, A/memory.current = 6G - * //\\ - * BC DE B/memory.low = 3G B/memory.current = 2G - * C/memory.low = 1G C/memory.current = 2G - * D/memory.low = 0 D/memory.current = 2G - * E/memory.low = 10G E/memory.current = 0 - * - * and the memory pressure is applied, the following memory distribution - * is expected (approximately): - * - * A/memory.current = 2G - * - * B/memory.current = 1.3G - * C/memory.current = 0.6G - * D/memory.current = 0 - * E/memory.current = 0 - * - * These calculations require constant tracking of the actual low usages - * (see propagate_protected_usage()), as well as recursive calculation of - * effective memory.low values. But as we do call mem_cgroup_protected() - * path for each memory cgroup top-down from the reclaim, - * it's possible to optimize this part, and save calculated elow - * for next usage. This part is intentionally racy, but it's ok, - * as memory.low is a best-effort mechanism. */ enum mem_cgroup_protection mem_cgroup_protected(struct mem_cgroup *root, struct mem_cgroup *memcg) { struct mem_cgroup *parent; - unsigned long emin, parent_emin; - unsigned long elow, parent_elow; unsigned long usage; if (mem_cgroup_disabled()) @@ -6322,52 +6336,29 @@ enum mem_cgroup_protection mem_cgroup_protected(struct mem_cgroup *root, if (!usage) return MEMCG_PROT_NONE; - emin = memcg->memory.min; - elow = memcg->memory.low; - parent = parent_mem_cgroup(memcg); /* No parent means a non-hierarchical mode on v1 memcg */ if (!parent) return MEMCG_PROT_NONE; - if (parent == root) - goto exit; - - parent_emin = READ_ONCE(parent->memory.emin); - emin = min(emin, parent_emin); - if (emin && parent_emin) { - unsigned long min_usage, siblings_min_usage; - - min_usage = min(usage, memcg->memory.min); - siblings_min_usage = atomic_long_read( - &parent->memory.children_min_usage); - - if (min_usage && siblings_min_usage) - emin = min(emin, parent_emin * min_usage / - siblings_min_usage); + if (parent == root) { + memcg->memory.emin = memcg->memory.min; + memcg->memory.elow = memcg->memory.low; + goto out; } - parent_elow = READ_ONCE(parent->memory.elow); - elow = min(elow, parent_elow); - if (elow && parent_elow) { - unsigned long low_usage, siblings_low_usage; - - low_usage = min(usage, memcg->memory.low); - siblings_low_usage = atomic_long_read( - &parent->memory.children_low_usage); + memcg->memory.emin = effective_protection(usage, + memcg->memory.min, READ_ONCE(parent->memory.emin), + atomic_long_read(&parent->memory.children_min_usage)); - if (low_usage && siblings_low_usage) - elow = min(elow, parent_elow * low_usage / - siblings_low_usage); - } + memcg->memory.elow = effective_protection(usage, + memcg->memory.low, READ_ONCE(parent->memory.elow), + atomic_long_read(&parent->memory.children_low_usage)); -exit: - memcg->memory.emin = emin; - memcg->memory.elow = elow; - - if (usage <= emin) +out: + if (usage <= memcg->memory.emin) return MEMCG_PROT_MIN; - else if (usage <= elow) + else if (usage <= memcg->memory.elow) return MEMCG_PROT_LOW; else return MEMCG_PROT_NONE; |