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SubjectRe: [PATCH -V8 11/16] hugetlb/cgroup: Add charge/uncharge routines for hugetlb cgroup
(2012/06/09 17:59), Aneesh Kumar K.V wrote:
> From: "Aneesh Kumar K.V"<aneesh.kumar@linux.vnet.ibm.com>
>
> This patchset add the charge and uncharge routines for hugetlb cgroup.
> This will be used in later patches when we allocate/free HugeTLB
> pages.
>
> Signed-off-by: Aneesh Kumar K.V<aneesh.kumar@linux.vnet.ibm.com>


I'm sorry if following has been already pointed out.

> ---
> mm/hugetlb_cgroup.c | 87 +++++++++++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 87 insertions(+)
>
> diff --git a/mm/hugetlb_cgroup.c b/mm/hugetlb_cgroup.c
> index 20a32c5..48efd5a 100644
> --- a/mm/hugetlb_cgroup.c
> +++ b/mm/hugetlb_cgroup.c
> @@ -105,6 +105,93 @@ static int hugetlb_cgroup_pre_destroy(struct cgroup *cgroup)
> return -EBUSY;
> }
>
> +int hugetlb_cgroup_charge_page(int idx, unsigned long nr_pages,
> + struct hugetlb_cgroup **ptr)
> +{
> + int ret = 0;
> + struct res_counter *fail_res;
> + struct hugetlb_cgroup *h_cg = NULL;
> + unsigned long csize = nr_pages * PAGE_SIZE;
> +
> + if (hugetlb_cgroup_disabled())
> + goto done;
> + /*
> + * We don't charge any cgroup if the compound page have less
> + * than 3 pages.
> + */
> + if (hstates[idx].order< 2)
> + goto done;
> +again:
> + rcu_read_lock();
> + h_cg = hugetlb_cgroup_from_task(current);
> + if (!h_cg)
> + h_cg = root_h_cgroup;
> +
> + if (!css_tryget(&h_cg->css)) {
> + rcu_read_unlock();
> + goto again;
> + }
> + rcu_read_unlock();
> +
> + ret = res_counter_charge(&h_cg->hugepage[idx], csize,&fail_res);
> + css_put(&h_cg->css);
> +done:
> + *ptr = h_cg;
> + return ret;
> +}
> +

Memory cgroup uses very complicated 'charge' routine for handling pageout...
which gets sleep.

For hugetlbfs, it has not sleep routine, you can do charge in simple way.
I guess...get/put here is overkill.

For example, h_cg cannot be freed while it has tasks. So, if 'current' is
belongs to the cgroup, it cannot be disappear. Then, you don't need get/put,
additional atomic ops for holding cgroup.

rcu_read_lock();
h_cg = hugetlb_cgroup_from_task(current);
ret = res_counter_charge(&h_cg->hugetpage[idx], csize, &fail_res);
rcu_read_unlock();

return ret;

Thanks,
-Kame



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