YAMAMOTO Takashi wrote:
>> -int res_counter_charge(struct res_counter *counter, unsigned long val)
>> +int res_counter_charge(struct res_counter *counter, unsigned long val,
>> + struct res_counter **limit_exceeded_at)
>> {
>> int ret;
>> unsigned long flags;
>> + struct res_counter *c, *unroll_c;
>>
>> - spin_lock_irqsave(&counter->lock, flags);
>> - ret = res_counter_charge_locked(counter, val);
>> - spin_unlock_irqrestore(&counter->lock, flags);
>> + *limit_exceeded_at = NULL;
>> + local_irq_save(flags);
>> + for (c = counter; c != NULL; c = c->parent) {
>> + spin_lock(&c->lock);
>> + ret = res_counter_charge_locked(c, val);
>> + spin_unlock(&c->lock);
>> + if (ret < 0) {
>> + *limit_exceeded_at = c;
>> + goto unroll;
>> + }
>> + }
>> + local_irq_restore(flags);
>> + return 0;
>> +
>> +unroll:
>> + for (unroll_c = counter; unroll_c != c; unroll_c = unroll_c->parent) {
>> + spin_lock(&unroll_c->lock);
>> + res_counter_uncharge_locked(unroll_c, val);
>> + spin_unlock(&unroll_c->lock);
>> + }
>> + local_irq_restore(flags);
>> return ret;
>> }
>
> i wonder how much performance impacts this involves.
>
> it increases the number of atomic ops per charge/uncharge and
> makes the common case (success) of every charge/uncharge in a system
> touch a global (ie. root cgroup's) cachelines.
>
Yes, it does. I'll run some tests to see what the overhead looks like. The
multi-hierarchy feature is very useful though and one of the TODOs is to make
the feature user selectable (possibly at run-time)
>> + /*
>> + * Ideally we need to hold cgroup_mutex here
>> + */
>> + list_for_each_entry_safe_from(cgroup, cgrp,
>> + &curr_cgroup->children, sibling) {
>> + struct mem_cgroup *mem_child;
>> +
>> + mem_child = mem_cgroup_from_cont(cgroup);
>> + ret = try_to_free_mem_cgroup_pages(mem_child,
>> + gfp_mask);
>> + mem->last_scanned_child = mem_child;
>> + if (ret == 0)
>> + break;
>> + }
>
> if i read it correctly, it makes us hit the last child again and again.
>
Hmm.. it should probably be set at the beginining of the loop. I'll retest
> i think you want to reclaim from all cgroups under the curr_cgroup
> including eg. children's children.
>
Yes, good point, I should break out the function, so that we can work around the
recursion problem. Charging can cause further recursion, since we check for
last_counter.
> YAMAMOTO Takashi
--
Warm Regards,
Balbir Singh
Linux Technology Center
IBM, ISTL
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