Re: Low overhead patches for the memory cgroup controller (v5)

From: Andrew Morton
Date: Mon Jun 22 2009 - 18:44:14 EST


On Mon, 15 Jun 2009 10:09:00 +0530
Balbir Singh <balbir@xxxxxxxxxxxxxxxxxx> wrote:

>
> ...
>
> This patch changes the memory cgroup and removes the overhead associated
> with accounting all pages in the root cgroup. As a side-effect, we can
> no longer set a memory hard limit in the root cgroup.
>
> A new flag to track whether the page has been accounted or not
> has been added as well. Flags are now set atomically for page_cgroup,
> pcg_default_flags is now obsolete and removed.
>
> ...
>
> @@ -1114,9 +1121,22 @@ static void __mem_cgroup_commit_charge(struct mem_cgroup *mem,
> css_put(&mem->css);
> return;
> }
> +
> pc->mem_cgroup = mem;
> smp_wmb();
> - pc->flags = pcg_default_flags[ctype];
> + switch (ctype) {
> + case MEM_CGROUP_CHARGE_TYPE_CACHE:
> + case MEM_CGROUP_CHARGE_TYPE_SHMEM:
> + SetPageCgroupCache(pc);
> + SetPageCgroupUsed(pc);
> + break;
> + case MEM_CGROUP_CHARGE_TYPE_MAPPED:
> + ClearPageCgroupCache(pc);
> + SetPageCgroupUsed(pc);
> + break;
> + default:
> + break;
> + }

Do we still need the smp_wmb()?

It's hard to say, because we forgot to document it :(
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