linux-kernel - Re: [PATCH 2/2] mm/page_alloc: remove unnecessary parameter batch of nr_pcp

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Date:   Tue, 15 Aug 2023 10:46:55 -0700
From:   Chris Li <chrisl@...nel.org>
To:     Kemeng Shi <shikemeng@...weicloud.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        akpm@...ux-foundation.org, baolin.wang@...ux.alibaba.com,
        mgorman@...hsingularity.net, david@...hat.com, willy@...radead.org
Subject: Re: [PATCH 2/2] mm/page_alloc: remove unnecessary parameter batch of
 nr_pcp_free

Hi Kemeng,

Since I am discussing the other patch in this series, I might just commend on this one
as well.

On Wed, Aug 09, 2023 at 06:07:54PM +0800, Kemeng Shi wrote:
> We get batch from pcp and just pass it to nr_pcp_free immediately. Get
> batch from pcp inside nr_pcp_free to remove unnecessary parameter batch.
> 
> Signed-off-by: Kemeng Shi <shikemeng@...weicloud.com>
> ---
>  mm/page_alloc.c | 8 +++-----
>  1 file changed, 3 insertions(+), 5 deletions(-)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 1ddcb2707d05..bb1d14e806ad 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -2376,10 +2376,10 @@ static bool free_unref_page_prepare(struct page *page, unsigned long pfn,
>  	return true;
>  }
>  
> -static int nr_pcp_free(struct per_cpu_pages *pcp, int high, int batch,
> -		       bool free_high)
> +static int nr_pcp_free(struct per_cpu_pages *pcp, int high, bool free_high)
>  {
>  	int min_nr_free, max_nr_free;
> +	int batch = READ_ONCE(pcp->batch);

Because nr_pcp_free is static and has only one caller. This function gets inlined
at the caller's side. I verified that on X86_64 compiled code.

So this fix in my opinion is not worthwhile to fix. It will produce the same
machine code. One minor side effect is that it will hide the commit under it
in "git blame".

Chris