On Fri, 07 Mar 2008 18:32:20 +0300
Pavel Emelyanov <[EMAIL PROTECTED]> wrote:
> This allows us two things basically:
>
> 1. If the subgroup has the limit higher than its parent has
> then the one will get more memory than allowed.
> 2. When we will need to account for a resource in more than
> one place, we'll be able to use this technics.
>
> Look, consider we have a memory limit and swap limit. The
> memory limit is the limit for the sum of RSS, page cache
> and swap usage. To account for this gracefuly, we'll set
> two counters:
>
> res_counter mem_counter;
> res_counter swap_counter;
>
> attach mm to the swap one
>
> mm->mem_cnt = &swap_counter;
>
> and make the swap_counter be mem's child. That's it. If we
> want hierarchical support, then the tree will look like this:
>
> mem_counter_top
> swap_counter_top <- mm_struct living at top
> mem_counter_sub
> swap_counter_sub <- mm_struct living at sub
>
Hmm? seems strange.
IMO, a parent's usage is just sum of all childs'.
And, historically, memory overcommit is done agaist "memory usage + swap".
How about this ?
<mem_counter_top, swap_counter_top>
<mem_counter_sub, swap_counter_sub>
<mem_counter_sub, swap_counter_sub>
<mem_counter_sub, swap_counter_sub>
mem_counter_top.usage == sum of all mem_coutner_sub.usage
swap_counter_sub.usage = sum of all swap_counter_sub.usage
> @@ -976,19 +976,22 @@ static void free_mem_cgroup_per_zone_info(struct
> mem_cgroup *mem, int node)
> static struct cgroup_subsys_state *
> mem_cgroup_create(struct cgroup_subsys *ss, struct cgroup *cont)
> {
> - struct mem_cgroup *mem;
> + struct mem_cgroup *mem, *parent;
> int node;
>
> if (unlikely((cont->parent) == NULL)) {
> mem = &init_mem_cgroup;
> init_mm.mem_cgroup = mem;
> - } else
> + parent = NULL;
> + } else {
> mem = kzalloc(sizeof(struct mem_cgroup), GFP_KERNEL);
> + parent = mem_cgroup_from_cont(cont->parent);
> + }
>
> if (mem == NULL)
> return ERR_PTR(-ENOMEM);
>
> - res_counter_init(&mem->res);
> + res_counter_init(&mem->res, parent ? &parent->res : NULL);
>
I have no objection to add some hierarchical support to res_counter.
But we should wait to add it to mem_cgroup because we have to add
some amount of codes to handle hierarchy under mem_cgroup in reasonable way.
for example)
- hierarchical memory reclaim
- keeping fairness between sub memory controllers.
etc...
Thanks,
-Kame
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