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    SubjectRe: [PATCH -V5 12/14] memcg: move HugeTLB resource count to parent cgroup on memcg removal
    (2012/04/07 3:50), Aneesh Kumar K.V wrote:

    > From: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
    >
    > This add support for memcg removal with HugeTLB resource usage.
    >
    > Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>


    Hmm


    > +#ifdef CONFIG_MEM_RES_CTLR_HUGETLB
    > +/*
    > + * Force the memcg to empty the hugetlb resources by moving them to
    > + * the parent cgroup. We can fail if the parent cgroup's limit prevented
    > + * the charging. This should only happen if use_hierarchy is not set.
    > + */
    > +int hugetlb_force_memcg_empty(struct cgroup *cgroup)
    > +{
    > + struct hstate *h;
    > + struct page *page;
    > + int ret = 0, idx = 0;
    > +
    > + do {
    > + if (cgroup_task_count(cgroup) || !list_empty(&cgroup->children))
    > + goto out;
    > + /*
    > + * If the task doing the cgroup_rmdir got a signal
    > + * we don't really need to loop till the hugetlb resource
    > + * usage become zero.
    > + */
    > + if (signal_pending(current)) {
    > + ret = -EINTR;
    > + goto out;
    > + }
    > + for_each_hstate(h) {
    > + spin_lock(&hugetlb_lock);
    > + list_for_each_entry(page, &h->hugepage_activelist, lru) {
    > + ret = mem_cgroup_move_hugetlb_parent(idx, cgroup, page);
    > + if (ret) {
    > + spin_unlock(&hugetlb_lock);
    > + goto out;
    > + }
    > + }
    > + spin_unlock(&hugetlb_lock);
    > + idx++;
    > + }
    > + cond_resched();
    > + } while (mem_cgroup_have_hugetlb_usage(cgroup));
    > +out:
    > + return ret;
    > +}
    > +#endif
    > +
    > /* Should be called on processing a hugepagesz=... option */
    > void __init hugetlb_add_hstate(unsigned order)
    > {
    > diff --git a/mm/memcontrol.c b/mm/memcontrol.c
    > index 7d3330e..7b6e79a 100644
    > --- a/mm/memcontrol.c
    > +++ b/mm/memcontrol.c
    > @@ -3228,9 +3228,11 @@ static inline int mem_cgroup_move_swap_account(swp_entry_t entry,
    > #endif
    >
    > #ifdef CONFIG_MEM_RES_CTLR_HUGETLB
    > -static bool mem_cgroup_have_hugetlb_usage(struct mem_cgroup *memcg)
    > +bool mem_cgroup_have_hugetlb_usage(struct cgroup *cgroup)
    > {
    > int idx;
    > + struct mem_cgroup *memcg = mem_cgroup_from_cont(cgroup);
    > +
    > for (idx = 0; idx < hugetlb_max_hstate; idx++) {
    > if ((res_counter_read_u64(&memcg->hugepage[idx], RES_USAGE)) > 0)
    > return 1;
    > @@ -3328,10 +3330,57 @@ void mem_cgroup_hugetlb_uncharge_memcg(int idx, unsigned long nr_pages,
    > res_counter_uncharge(&memcg->hugepage[idx], csize);
    > return;
    > }
    > -#else
    > -static bool mem_cgroup_have_hugetlb_usage(struct mem_cgroup *memcg)
    > +
    > +int mem_cgroup_move_hugetlb_parent(int idx, struct cgroup *cgroup,
    > + struct page *page)
    > {
    > - return 0;
    > + struct page_cgroup *pc;
    > + int csize, ret = 0;
    > + struct res_counter *fail_res;
    > + struct cgroup *pcgrp = cgroup->parent;
    > + struct mem_cgroup *parent = mem_cgroup_from_cont(pcgrp);
    > + struct mem_cgroup *memcg = mem_cgroup_from_cont(cgroup);
    > +
    > + if (!get_page_unless_zero(page))
    > + goto out;
    > +
    > + pc = lookup_page_cgroup(page);
    > + lock_page_cgroup(pc);
    > + if (!PageCgroupUsed(pc) || pc->mem_cgroup != memcg)
    > + goto err_out;
    > +
    > + csize = PAGE_SIZE << compound_order(page);
    > + /*
    > + * uncharge from child and charge the parent. If we have
    > + * use_hierarchy set, we can never fail here. In-order to make
    > + * sure we don't get -ENOMEM on parent charge, we first uncharge
    > + * the child and then charge the parent.
    > + */
    > + if (parent->use_hierarchy) {


    > + res_counter_uncharge(&memcg->hugepage[idx], csize);
    > + if (!mem_cgroup_is_root(parent))
    > + ret = res_counter_charge(&parent->hugepage[idx],
    > + csize, &fail_res);


    Ah, why is !mem_cgroup_is_root() checked ? no res_counter update for
    root cgroup ?

    I think it's better to have res_counter_move_parent()...to do ops in atomic.
    (I'll post a patch for that for my purpose). OR, just ignore res->usage if
    parent->use_hierarchy == 1.

    uncharge->charge will have a race.

    > + } else {
    > + if (!mem_cgroup_is_root(parent)) {
    > + ret = res_counter_charge(&parent->hugepage[idx],
    > + csize, &fail_res);
    > + if (ret) {
    > + ret = -EBUSY;
    > + goto err_out;
    > + }
    > + }
    > + res_counter_uncharge(&memcg->hugepage[idx], csize);
    > + }


    Just a notice. Recently, Tejun changed failure of pre_destory() to show WARNING.
    Then, I'd like to move the usage to the root cgroup if use_hierarchy=0.
    Will it work for you ?

    > + /*
    > + * caller should have done css_get
    > + */


    Could you explain meaning of this comment ?


    Thanks,
    -Kame

    > + pc->mem_cgroup = parent;
    > +err_out:
    > + unlock_page_cgroup(pc);
    > + put_page(page);
    > +out:
    > + return ret;
    > }
    > #endif /* CONFIG_MEM_RES_CTLR_HUGETLB */
    >
    > @@ -3852,6 +3901,11 @@ static int mem_cgroup_force_empty(struct mem_cgroup *memcg, bool free_all)
    > /* should free all ? */
    > if (free_all)
    > goto try_to_free;
    > +
    > + /* move the hugetlb charges */
    > + ret = hugetlb_force_memcg_empty(cgrp);
    > + if (ret)
    > + goto out;
    > move_account:
    > do {
    > ret = -EBUSY;
    > @@ -5172,12 +5226,6 @@ free_out:
    > static int mem_cgroup_pre_destroy(struct cgroup *cont)
    > {
    > struct mem_cgroup *memcg = mem_cgroup_from_cont(cont);
    > - /*
    > - * Don't allow memcg removal if we have HugeTLB resource
    > - * usage.
    > - */
    > - if (mem_cgroup_have_hugetlb_usage(memcg))
    > - return -EBUSY;
    >
    > return mem_cgroup_force_empty(memcg, false);
    > }





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