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

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Date:   Tue, 2 Mar 2021 07:05:35 +0000
From:   "Zhouguanghui (OS Kernel)" <zhouguanghui1@...wei.com>
To:     Zi Yan <ziy@...dia.com>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "npiggin@...e.de" <npiggin@...e.de>,
        "Wangkefeng (OS Kernel Lab)" <wangkefeng.wang@...wei.com>,
        "Guohanjun (Hanjun Guo)" <guohanjun@...wei.com>,
        Dingtianhong <dingtianhong@...wei.com>,
        Chenweilong <chenweilong@...wei.com>,
        "Xiangrui (Euler)" <rui.xiang@...wei.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>
Subject: Re: [PATCH] mm/memcg: set memcg when split pages

在 2021/3/2 10:00, Zi Yan 写道:
> On 1 Mar 2021, at 20:34, 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.
>>
>> Signed-off-by: Zhou Guanghui <zhouguanghui1@...wei.com>
>> ---
>>   include/linux/memcontrol.h | 10 ++++++++++
>>   mm/page_alloc.c            |  4 +++-
>>   2 files changed, 13 insertions(+), 1 deletion(-)
>>
>> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
>> index e6dc793d587d..c7e2b4421dc1 100644
>> --- a/include/linux/memcontrol.h
>> +++ b/include/linux/memcontrol.h
>> @@ -867,6 +867,12 @@ void mem_cgroup_print_oom_group(struct mem_cgroup *memcg);
>>   extern bool cgroup_memory_noswap;
>>   #endif
>>
>> +static inline void copy_page_memcg(struct page *dst, struct page *src)
>> +{
>> +	if (src->memcg_data)
>> +		dst->memcg_data = src->memcg_data;
>> +}
>> +
>>   struct mem_cgroup *lock_page_memcg(struct page *page);
>>   void __unlock_page_memcg(struct mem_cgroup *memcg);
>>   void unlock_page_memcg(struct page *page);
>> @@ -1291,6 +1297,10 @@ mem_cgroup_print_oom_meminfo(struct mem_cgroup *memcg)
>>   {
>>   }
>>
>> +static inline void copy_page_memcg(struct page *dst, struct page *src)
>> +{
>> +}
>> +
>>   static inline struct mem_cgroup *lock_page_memcg(struct page *page)
>>   {
>>   	return NULL;
>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>> index 3e4b29ee2b1e..ee0a63dc1c9b 100644
>> --- a/mm/page_alloc.c
>> +++ b/mm/page_alloc.c
>> @@ -3307,8 +3307,10 @@ void split_page(struct page *page, unsigned int order)
>>   	VM_BUG_ON_PAGE(PageCompound(page), page);
>>   	VM_BUG_ON_PAGE(!page_count(page), page);
>>
>> -	for (i = 1; i < (1 << order); i++)
>> +	for (i = 1; i < (1 << order); i++) {
>>   		set_page_refcounted(page + i);
>> +		copy_page_memcg(page + i, page);
>> +	}
>>   	split_page_owner(page, 1 << order);
>>   }
>>   EXPORT_SYMBOL_GPL(split_page);
>> -- 
>> 2.25.0
> 
> +memcg maintainers
> 
> split_page() is used for non-compound higher-order pages. I am not sure
> if there is any such pages monitored by memcg. Please let me know
> if I miss anything.

Thank you for taking time for this.

This should be put in kmemcg, and I'll modify it.

When the kmemcg is enabled and _GFP_ACCOUNT is set, the charged and 
uncharged sizes do not match when alloc/free_pages_exact method is used 
to apply for or free memory with exact size. This is because memcg data 
of the tail page is not set during the split page.