Re: [PATCH v2 0/7] mm: pages for hugetlb's overcommit may be able to charge to memcg

[TSUKADA Koutaro]

Hi Punit,

On 2018/05/21 23:52, Punit Agrawal wrote:
> Hi Tsukada,
> 
> I was staring at memcg code to better understand your changes and had
> the below thought.
> 
> TSUKADA Koutaro <tsukada@xxxxxxxxxxxx> writes:
> 
> [...]
> 
>> In this patch-set, introduce the charge_surplus_huge_pages(boolean) to
>> struct hstate. If it is true, it charges to the memory cgroup to which the
>> task that obtained surplus hugepages belongs. If it is false, do nothing as
>> before, and the default value is false. The charge_surplus_huge_pages can
>> be controlled procfs or sysfs interfaces.
> 
> Instead of tying the surplus huge page charging control per-hstate,
> could the control be made per-memcg?
> 
> This can be done by introducing a per-memory controller file in sysfs
> (memory.charge_surplus_hugepages?) that indicates whether surplus
> hugepages are to be charged to the controller and forms part of the
> total limit. IIUC, the limit already accounts for page and swap cache
> pages.
> 
> This would allow the control to be enabled per-cgroup and also keep the
> userspace control interface in one place.
> 
> As said earlier, I'm not familiar with memcg so the above might not be a
> feasible but think it'll lead to a more coherent user
> interface. Hopefully, more knowledgeable folks on the thread can chime
> in.
> 

Thank you for good advise.
As you mentioned, it is better to be able to control by per-memcg. After
organizing my thoughts, I will develop the next version patch-set that can
solve issues and challenge again.

Thanks,
Tsukada

> Thanks,
> Punit
> 
>> Since THP is very effective in environments with kernel page size of 4KB,
>> such as x86, there is no reason to positively use HugeTLBfs, so I think
>> that there is no situation to enable charge_surplus_huge_pages. However, in
>> some distributions such as arm64, the page size of the kernel is 64KB, and
>> the size of THP is too huge as 512MB, making it difficult to use. HugeTLBfs
>> may support multiple huge page sizes, and in such a special environment
>> there is a desire to use HugeTLBfs.
>>
>> The patch set is for 4.17.0-rc3+. I don't know whether patch-set are
>> acceptable or not, so I just done a simple test.
>>
>> Thanks,
>> Tsukada
>>
>> TSUKADA Koutaro (7):
>>   hugetlb: introduce charge_surplus_huge_pages to struct hstate
>>   hugetlb: supports migrate charging for surplus hugepages
>>   memcg: use compound_order rather than hpage_nr_pages
>>   mm, sysctl: make charging surplus hugepages controllable
>>   hugetlb: add charge_surplus_hugepages attribute
>>   Documentation, hugetlb: describe about charge_surplus_hugepages
>>   memcg: supports movement of surplus hugepages statistics
>>
>>  Documentation/vm/hugetlbpage.txt |    6 +
>>  include/linux/hugetlb.h          |    4 +
>>  kernel/sysctl.c                  |    7 +
>>  mm/hugetlb.c                     |  148 +++++++++++++++++++++++++++++++++++++++
>>  mm/memcontrol.c                  |  109 +++++++++++++++++++++++++++-
>>  5 files changed, 269 insertions(+), 5 deletions(-)