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Message-ID: <87d37wetd7.fsf@skywalker.in.ibm.com>
Date: Wed, 28 Mar 2012 19:10:36 +0530
From: "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
To: Michal Hocko <mhocko@...e.cz>
Cc: linux-mm@...ck.org, mgorman@...e.de,
kamezawa.hiroyu@...fujitsu.com, dhillf@...il.com,
aarcange@...hat.com, akpm@...ux-foundation.org, hannes@...xchg.org,
linux-kernel@...r.kernel.org, cgroups@...r.kernel.org
Subject: Re: [PATCH -V4 04/10] memcg: Add HugeTLB extension
Michal Hocko <mhocko@...e.cz> writes:
> On Fri 16-03-12 23:09:24, Aneesh Kumar K.V wrote:
>> From: "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
>>
>> This patch implements a memcg extension that allows us to control
>> HugeTLB allocations via memory controller.
>
> And the infrastructure is not used at this stage (you forgot to
> mention).
> The changelog should be much more descriptive.
Will update the changelog.
>
>>
>> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@...ux.vnet.ibm.com>
>> ---
>> include/linux/hugetlb.h | 1 +
>> include/linux/memcontrol.h | 42 +++++++++++++
>> init/Kconfig | 8 +++
>> mm/hugetlb.c | 2 +-
>> mm/memcontrol.c | 138 ++++++++++++++++++++++++++++++++++++++++++++
>> 5 files changed, 190 insertions(+), 1 deletions(-)
>>
> [...]
>> diff --git a/init/Kconfig b/init/Kconfig
>> index 3f42cd6..f0eb8aa 100644
>> --- a/init/Kconfig
>> +++ b/init/Kconfig
>> @@ -725,6 +725,14 @@ config CGROUP_PERF
>>
>> Say N if unsure.
>>
>> +config MEM_RES_CTLR_HUGETLB
>> + bool "Memory Resource Controller HugeTLB Extension (EXPERIMENTAL)"
>> + depends on CGROUP_MEM_RES_CTLR && HUGETLB_PAGE && EXPERIMENTAL
>> + default n
>> + help
>> + Add HugeTLB management to memory resource controller. When you
>> + enable this, you can put a per cgroup limit on HugeTLB usage.
>
> How does it interact with the hard/soft limists etc...
There is no softlimit support for HugeTLB extension.
>
> [...]
>> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
>> index 6728a7a..4b36c5e 100644
>> --- a/mm/memcontrol.c
>> +++ b/mm/memcontrol.c
>> @@ -235,6 +235,10 @@ struct mem_cgroup {
>> */
>> struct res_counter memsw;
>> /*
>> + * the counter to account for hugepages from hugetlb.
>> + */
>> + struct res_counter hugepage[HUGE_MAX_HSTATE];
>> + /*
>> * Per cgroup active and inactive list, similar to the
>> * per zone LRU lists.
>> */
>> @@ -3156,6 +3160,128 @@ 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)
>> +{
>> + int idx;
>> + for (idx = 0; idx < hugetlb_max_hstate; idx++) {
>
> Maybe we should expose for_each_hstate as well...
That will not really help here. If we use for_each_hstate then we will
need to use hstate_index to get the index.
>
>> + if (memcg->hugepage[idx].usage > 0)
>> + return 1;
>> + }
>> + return 0;
>> +}
>> +
>> +int mem_cgroup_hugetlb_charge_page(int idx, unsigned long nr_pages,
>> + struct mem_cgroup **ptr)
>> +{
>> + int ret = 0;
>> + struct mem_cgroup *memcg;
>> + struct res_counter *fail_res;
>> + unsigned long csize = nr_pages * PAGE_SIZE;
>> +
>> + if (mem_cgroup_disabled())
>> + return 0;
>> +again:
>> + rcu_read_lock();
>> + memcg = mem_cgroup_from_task(current);
>> + if (!memcg)
>> + memcg = root_mem_cgroup;
>> + if (mem_cgroup_is_root(memcg)) {
>> + rcu_read_unlock();
>> + goto done;
>> + }
>> + if (!css_tryget(&memcg->css)) {
>> + rcu_read_unlock();
>> + goto again;
>> + }
>> + rcu_read_unlock();
>> +
>> + ret = res_counter_charge(&memcg->hugepage[idx], csize, &fail_res);
>> + css_put(&memcg->css);
>> +done:
>> + *ptr = memcg;
>
> Why do we set ptr even for the failure case after we dropped a
> reference?
That ensures that *ptr is NULL.
>
>> + return ret;
>> +}
>> +
>> +void mem_cgroup_hugetlb_commit_charge(int idx, unsigned long nr_pages,
>> + struct mem_cgroup *memcg,
>> + struct page *page)
>> +{
>> + struct page_cgroup *pc;
>> +
>> + if (mem_cgroup_disabled())
>> + return;
>> +
>> + pc = lookup_page_cgroup(page);
>> + lock_page_cgroup(pc);
>> + if (unlikely(PageCgroupUsed(pc))) {
>> + unlock_page_cgroup(pc);
>> + mem_cgroup_hugetlb_uncharge_memcg(idx, nr_pages, memcg);
>> + return;
>> + }
>> + pc->mem_cgroup = memcg;
>> + /*
>> + * We access a page_cgroup asynchronously without lock_page_cgroup().
>> + * Especially when a page_cgroup is taken from a page, pc->mem_cgroup
>> + * is accessed after testing USED bit. To make pc->mem_cgroup visible
>> + * before USED bit, we need memory barrier here.
>> + * See mem_cgroup_add_lru_list(), etc.
>> + */
>> + smp_wmb();
>
> Is this really necessary for hugetlb pages as well?
I used to do that in cgroup_rmdir path, I later changed that part of the code. I
will look at the patches again to see if we really need this.
>
>> + SetPageCgroupUsed(pc);
>> +
>> + unlock_page_cgroup(pc);
>> + return;
>> +}
>> +
> [...]
>> @@ -4887,6 +5013,7 @@ err_cleanup:
>> static struct cgroup_subsys_state * __ref
>> mem_cgroup_create(struct cgroup_subsys *ss, struct cgroup *cont)
>> {
>> + int idx;
>> struct mem_cgroup *memcg, *parent;
>> long error = -ENOMEM;
>> int node;
>> @@ -4929,9 +5056,14 @@ mem_cgroup_create(struct cgroup_subsys *ss, struct cgroup *cont)
>> * mem_cgroup(see mem_cgroup_put).
>> */
>> mem_cgroup_get(parent);
>> + for (idx = 0; idx < HUGE_MAX_HSTATE; idx++)
>
> Do we have to init all hstates or is hugetlb_max_hstate enough?
Yes. we do call mem_cgroup_create for root cgroup before initialzing
hugetlb hstate.
>
>> + res_counter_init(&memcg->hugepage[idx],
>> + &parent->hugepage[idx]);
>> } else {
>> res_counter_init(&memcg->res, NULL);
>> res_counter_init(&memcg->memsw, NULL);
>> + for (idx = 0; idx < HUGE_MAX_HSTATE; idx++)
>> + res_counter_init(&memcg->hugepage[idx], NULL);
>
> Same here
> --
-aneesh
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