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SubjectRe: [PATCH -V8 12/16] hugetlb/cgroup: Add support for cgroup removal
On Mon 11-06-12 15:10:20, Aneesh Kumar K.V wrote:
> Michal Hocko <mhocko@suse.cz> writes:
[...]
> >> +static int hugetlb_cgroup_move_parent(int idx, struct cgroup *cgroup,
> >> + struct page *page)
> >
> > deserves a comment about the locking (needs to be called with
> > hugetlb_lock).
>
> will do
>
> >
> >> +{
> >> + int csize;
> >> + struct res_counter *counter;
> >> + struct res_counter *fail_res;
> >> + struct hugetlb_cgroup *page_hcg;
> >> + struct hugetlb_cgroup *h_cg = hugetlb_cgroup_from_cgroup(cgroup);
> >> + struct hugetlb_cgroup *parent = parent_hugetlb_cgroup(cgroup);
> >> +
> >> + if (!get_page_unless_zero(page))
> >> + goto out;
> >> +
> >> + page_hcg = hugetlb_cgroup_from_page(page);
> >> + /*
> >> + * We can have pages in active list without any cgroup
> >> + * ie, hugepage with less than 3 pages. We can safely
> >> + * ignore those pages.
> >> + */
> >> + if (!page_hcg || page_hcg != h_cg)
> >> + goto err_out;
> >
> > How can we have page_hcg != NULL && page_hcg != h_cg?
>
> pages belonging to other cgroup ?

OK, I've forgot that you are iterating over all active huge pages in
hugetlb_cgroup_pre_destroy. What prevents you from doing the filtering
in the caller?
I am also wondering why you need to play with the page reference
counting here. You are under hugetlb_lock so the page cannot disappear
in the meantime or am I missing something?
--
Michal Hocko
SUSE Labs
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9
Czech Republic


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