linux-kernel - Re: [PATCH v3 3/3] mm: page_counters: initialize usage using ATOMIC_LONG

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Message-ID: <20240726231110.GF1702603@cmpxchg.org>
Date: Fri, 26 Jul 2024 19:11:10 -0400
From: Johannes Weiner <hannes@...xchg.org>
To: Roman Gushchin <roman.gushchin@...ux.dev>
Cc: Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, Michal Hocko <mhocko@...nel.org>,
	Shakeel Butt <shakeel.butt@...ux.dev>,
	Muchun Song <muchun.song@...ux.dev>
Subject: Re: [PATCH v3 3/3] mm: page_counters: initialize usage using
 ATOMIC_LONG_INIT() macro

On Fri, Jul 26, 2024 at 08:31:10PM +0000, Roman Gushchin wrote:
> When a page_counter structure is initialized, there is no need to
> use an atomic set operation to initialize the usage counter because
> at this point the structure is not visible to anybody else.
> ATOMIC_LONG_INIT() is what should be used in such cases.
> 
> Signed-off-by: Roman Gushchin <roman.gushchin@...ux.dev>
> ---
>  include/linux/page_counter.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/include/linux/page_counter.h b/include/linux/page_counter.h
> index cf837d0f8ed1..5da11392b382 100644
> --- a/include/linux/page_counter.h
> +++ b/include/linux/page_counter.h
> @@ -53,7 +53,7 @@ static inline void page_counter_init(struct page_counter *counter,
>  				     struct page_counter *parent,
>  				     bool protection_support)
>  {
> -	atomic_long_set(&counter->usage, 0);
> +	counter->usage = (atomic_long_t)ATOMIC_LONG_INIT(0);

Pretty cool that ATOMIC_LONG_INIT() return value needs a cast to
atomic_long_t! ^_^

Acked-by: Johannes Weiner <hannes@...xchg.org>