linux-kernel - Re: [RFC PATCH 1/5] mm: memcg: make memcg huge page split support any order split.

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Date:   Mon, 21 Mar 2022 11:57:11 -0700
From:   Roman Gushchin <roman.gushchin@...ux.dev>
To:     Zi Yan <ziy@...dia.com>
Cc:     Matthew Wilcox <willy@...radead.org>, linux-mm@...ck.org,
        Shuah Khan <shuah@...nel.org>, Yang Shi <shy828301@...il.com>,
        Miaohe Lin <linmiaohe@...wei.com>,
        Hugh Dickins <hughd@...gle.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        linux-kernel@...r.kernel.org, cgroups@...r.kernel.org,
        linux-kselftest@...r.kernel.org
Subject: Re: [RFC PATCH 1/5] mm: memcg: make memcg huge page split support
 any order split.

On Mon, Mar 21, 2022 at 10:21:24AM -0400, Zi Yan wrote:
> From: Zi Yan <ziy@...dia.com>
> 
> It sets memcg information for the pages after the split. A new parameter
> new_order is added to tell the new page order, always 0 for now. It
> prepares for upcoming changes to support split huge page to any lower
> order.
> 
> Signed-off-by: Zi Yan <ziy@...dia.com>
> ---
>  include/linux/memcontrol.h |  2 +-
>  mm/huge_memory.c           |  2 +-
>  mm/memcontrol.c            | 10 +++++-----
>  mm/page_alloc.c            |  2 +-
>  4 files changed, 8 insertions(+), 8 deletions(-)
> 
> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index 89b14729d59f..e71189454bf0 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -1116,7 +1116,7 @@ static inline void memcg_memory_event_mm(struct mm_struct *mm,
>  	rcu_read_unlock();
>  }
>  
> -void split_page_memcg(struct page *head, unsigned int nr);
> +void split_page_memcg(struct page *head, unsigned int nr, unsigned int new_order);

It looks a bit inconsistent, can't we switch to use either nr or order for both
arguments? The latter is preferable.

Other than that, the patch looks good to me.

Thanks!