Re: [PATCH] mm/memcg: set memcg when split pages

[Zhouguanghui (OS Kernel)]

在 2021/3/3 15:46, Michal Hocko 写道:
> On Tue 02-03-21 17:56:07, Johannes Weiner wrote:
>> On Tue, Mar 02, 2021 at 12:24:41PM -0800, Hugh Dickins wrote:
>>> On Tue, 2 Mar 2021, Michal Hocko wrote:
>>>> [Cc Johannes for awareness and fixup Nick's email]
>>>>
>>>> On Tue 02-03-21 01:34:51, Zhou Guanghui wrote:
>>>>> When split page, the memory cgroup info recorded in first page is
>>>>> not copied to tail pages. In this case, when the tail pages are
>>>>> freed, the uncharge operation is not performed. As a result, the
>>>>> usage of this memcg keeps increasing, and the OOM may occur.
>>>>>
>>>>> So, the copying of first page's memory cgroup info to tail pages
>>>>> is needed when split page.
>>>>
>>>> I was not aware that alloc_pages_exact is used for accounted allocations
>>>> but git grep told me otherwise so this is not a theoretical one. Both
>>>> users (arm64 and s390 kvm) are quite recent AFAICS. split_page is also
>>>> used in dma allocator but I got lost in indirection so I have no idea
>>>> whether there are any users there.
>>>
>>> Yes, it's a bit worrying that such a low-level thing as split_page()
>>> can now get caught up in memcg accounting, but I suppose that's okay.
>>>
>>> I feel rather strongly that whichever way it is done, THP splitting
>>> and split_page() should use the same interface to memcg.
>>>
>>> And a look at mem_cgroup_split_huge_fixup() suggests that nowadays
>>> there need to be css_get()s too - or better, a css_get_many().
>>>
>>> Its #ifdef CONFIG_TRANSPARENT_HUGEPAGE should be removed, rename
>>> it mem_cgroup_split_page_fixup(), and take order from caller.
>>
>> +1
>>
>> There is already a split_page_owner() in both these places as well
>> which does a similar thing. Mabye we can match that by calling it
>> split_page_memcg() and having it take a nr of pages?
> 
> Sounds good to me.
> 
  Hi, Michal, Johannes, Hugh, and Zi Yan, thank you for taking time for 
this.

I agree, and will send v2 patches for taking these.

Thanks