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From:   "NeilBrown" <neilb@suse.de>
To:     "Miaohe Lin" <linmiaohe@huawei.com>
Cc:     akpm@linux-foundation.org, willy@infradead.org, vbabka@suse.cz,
        dhowells@redhat.com, apopple@nvidia.com, david@redhat.com,
        surenb@google.com, peterx@redhat.com, naoya.horiguchi@nec.com,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        linmiaohe@huawei.com
Subject: Re: [PATCH 11/15] mm/swap: add helper swap_offset_available()
In-reply-to: <20220509131416.17553-12-linmiaohe@huawei.com>
References: <20220509131416.17553-1-linmiaohe@huawei.com>,
 <20220509131416.17553-12-linmiaohe@huawei.com>
Date:   Tue, 10 May 2022 10:45:54 +1000
Message-id: <165214355418.14782.13896859043718755300@noble.neil.brown.name>
Precedence: bulk

On Mon, 09 May 2022, Miaohe Lin wrote:
> Add helper swap_offset_available() to remove some duplicated codes.
> Minor readability improvement.

I don't think that putting the spin_lock() inside the inline helper is
good for readability.
If the function was called
   swap_offset_available_and_locked()

it might be ok.  Otherwise I would rather the spin_lock() was called
when the function returned true.

Thanks,
NeilBrown

>=20
> Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
> ---
>  mm/swapfile.c | 33 +++++++++++++++++----------------
>  1 file changed, 17 insertions(+), 16 deletions(-)
>=20
> diff --git a/mm/swapfile.c b/mm/swapfile.c
> index c90298a0561a..d5d3e2d03d28 100644
> --- a/mm/swapfile.c
> +++ b/mm/swapfile.c
> @@ -776,6 +776,21 @@ static void set_cluster_next(struct swap_info_struct *=
si, unsigned long next)
>  	this_cpu_write(*si->cluster_next_cpu, next);
>  }
> =20
> +static inline bool swap_offset_available(struct swap_info_struct *si, unsi=
gned long offset)
> +{
> +	if (data_race(!si->swap_map[offset])) {
> +		spin_lock(&si->lock);
> +		return true;
> +	}
> +
> +	if (vm_swap_full() && READ_ONCE(si->swap_map[offset]) =3D=3D SWAP_HAS_CAC=
HE) {
> +		spin_lock(&si->lock);
> +		return true;
> +	}
> +
> +	return false;
> +}
> +
>  static int scan_swap_map_slots(struct swap_info_struct *si,
>  			       unsigned char usage, int nr,
>  			       swp_entry_t slots[])
> @@ -953,15 +968,8 @@ static int scan_swap_map_slots(struct swap_info_struct=
 *si,
>  scan:
>  	spin_unlock(&si->lock);
>  	while (++offset <=3D READ_ONCE(si->highest_bit)) {
> -		if (data_race(!si->swap_map[offset])) {
> -			spin_lock(&si->lock);
> +		if (swap_offset_available(si, offset))
>  			goto checks;
> -		}
> -		if (vm_swap_full() &&
> -		    READ_ONCE(si->swap_map[offset]) =3D=3D SWAP_HAS_CACHE) {
> -			spin_lock(&si->lock);
> -			goto checks;
> -		}
>  		if (unlikely(--latency_ration < 0)) {
>  			cond_resched();
>  			latency_ration =3D LATENCY_LIMIT;
> @@ -970,15 +978,8 @@ static int scan_swap_map_slots(struct swap_info_struct=
 *si,
>  	}
>  	offset =3D si->lowest_bit;
>  	while (offset < scan_base) {
> -		if (data_race(!si->swap_map[offset])) {
> -			spin_lock(&si->lock);
> +		if (swap_offset_available(si, offset))
>  			goto checks;
> -		}
> -		if (vm_swap_full() &&
> -		    READ_ONCE(si->swap_map[offset]) =3D=3D SWAP_HAS_CACHE) {
> -			spin_lock(&si->lock);
> -			goto checks;
> -		}
>  		if (unlikely(--latency_ration < 0)) {
>  			cond_resched();
>  			latency_ration =3D LATENCY_LIMIT;
> --=20
> 2.23.0
>=20
>=20