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

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Date:   Mon, 1 Mar 2021 20:59:47 -0500
From:   Zi Yan <ziy@...dia.com>
To:     Zhou Guanghui <zhouguanghui1@...wei.com>
CC:     <linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>,
        <akpm@...ux-foundation.org>, <npiggin@...e.de>,
        <wangkefeng.wang@...wei.com>, <guohanjun@...wei.com>,
        <dingtianhong@...wei.com>, <chenweilong@...wei.com>,
        <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

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.

—
Best Regards,
Yan Zi

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