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From:   Zi Yan <ziy@nvidia.com>
To:     Zhou Guanghui <zhouguanghui1@huawei.com>
CC:     <linux-kernel@vger.kernel.org>, <linux-mm@kvack.org>,
        <akpm@linux-foundation.org>, <mhocko@suse.com>,
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Subject: Re: [PATCH v2 2/2] mm/memcg: set memcg when split page
Date:   Thu, 4 Mar 2021 11:22:00 -0500
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In-Reply-To: <20210304074053.65527-3-zhouguanghui1@huawei.com>
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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@huawei.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 o=
rder)
>  	for (i =3D 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@nvidia.com>


=E2=80=94
Best Regards,
Yan Zi

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