linux-kernel - Re: [PATCH] mm: page_alloc: Remove redundant READ

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Message-ID: <87wmc3ufs4.fsf@DESKTOP-5N7EMDA>
Date: Wed, 02 Apr 2025 16:30:19 +0800
From: "Huang, Ying" <ying.huang@...ux.alibaba.com>
To: Songtang Liu <liusongtang@...edance.com>
Cc: akpm@...ux-foundation.org,  linux-mm@...ck.org,
  linux-kernel@...r.kernel.org,  zhengqi.arch@...edance.com,
  songmuchun@...edance.com
Subject: Re: [PATCH] mm: page_alloc: Remove redundant READ_ONCE

Songtang Liu <liusongtang@...edance.com> writes:

> In the current code, batch is a local variable, and it cannot be
> concurrently modified. It's unnecessary to use READ_ONCE here,
> so remove it.
>
> Fixes: 51a755c56dc0 ("mm: tune PCP high automatically")
> Signed-off-by: Songtang Liu <liusongtang@...edance.com>
> ---
>  mm/page_alloc.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index e3ea5bf5c459..6edc6e57d4f8 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -2661,7 +2661,7 @@ static void free_frozen_page_commit(struct zone *zone,
>  		free_high = (pcp->free_count >= batch &&
>  			     (pcp->flags & PCPF_PREV_FREE_HIGH_ORDER) &&
>  			     (!(pcp->flags & PCPF_FREE_HIGH_BATCH) ||
> -			      pcp->count >= READ_ONCE(batch)));
> +			      pcp->count >= batch));

Nice catch!

Reviewed-by: Huang Ying <ying.huang@...ux.alibaba.com>

>  		pcp->flags |= PCPF_PREV_FREE_HIGH_ORDER;
>  	} else if (pcp->flags & PCPF_PREV_FREE_HIGH_ORDER) {
>  		pcp->flags &= ~PCPF_PREV_FREE_HIGH_ORDER;

---
Best Regards,
Huang, Ying