linux-kernel - Re: [PATCH v2 2/2] mm/memcg: set memcg when split page

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Date:   Thu, 4 Mar 2021 11:22:00 -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>, <mhocko@...e.com>,
        <hannes@...xchg.org>, <hughd@...gle.com>,
        <kirill.shutemov@...ux.intel.com>, <npiggin@...il.com>,
        <wangkefeng.wang@...wei.com>, <guohanjun@...wei.com>,
        <dingtianhong@...wei.com>, <chenweilong@...wei.com>,
        <rui.xiang@...wei.com>
Subject: Re: [PATCH v2 2/2] mm/memcg: set memcg when split page

On 4 Mar 2021, at 2:40, Zhou Guanghui wrote:

> As described in the split_page function comment, for the non-compound
> high order page, the sub-pages must be freed individually. If the
> memcg of the fisrt page is valid, the tail pages cannot be uncharged

s/fisrt/first/

> when be freed.
>
> For example, when alloc_pages_exact is used to allocate 1MB continuous
> physical memory, 2MB is charged(kmemcg is enabled and __GFP_ACCOUNT is
> set). When make_alloc_exact free the unused 1MB and free_pages_exact
> free the applied 1MB, actually, only 4KB(one page) is uncharged.
>
> Therefore, the memcg of the tail page needs to be set when split page.
>
> Signed-off-by: Zhou Guanghui <zhouguanghui1@...wei.com>
> ---
>  mm/page_alloc.c | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 3e4b29ee2b1e..3ed783e25c3c 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -3310,6 +3310,7 @@ void split_page(struct page *page, unsigned int order)
>  	for (i = 1; i < (1 << order); i++)
>  		set_page_refcounted(page + i);
>  	split_page_owner(page, 1 << order);
> +	split_page_memcg(page, 1 << order);
>  }
>  EXPORT_SYMBOL_GPL(split_page);
>
> -- 
> 2.25.0

LGTM. Thanks.

Reviewed-by: Zi Yan <ziy@...dia.com>


—
Best Regards,
Yan Zi

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