linux-kernel - Re: [PATCH 3/4] mm/swapfile.c: compare tmp and max after trying to iterate on swap

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Message-ID: <87ftczt1cg.fsf@yhuang-dev.intel.com>
Date:   Mon, 20 Apr 2020 09:03:43 +0800
From:   "Huang\, Ying" <ying.huang@...el.com>
To:     Wei Yang <richard.weiyang@...il.com>
Cc:     <akpm@...ux-foundation.org>, <linux-mm@...ck.org>,
        <linux-kernel@...r.kernel.org>, <tim.c.chen@...ux.intel.com>
Subject: Re: [PATCH 3/4] mm/swapfile.c: compare tmp and max after trying to iterate on swap_map

Wei Yang <richard.weiyang@...il.com> writes:

> There are two duplicate code to handle the case when there is no
> available swap entry. Just let the code go through and do the check at
> second place.
>
> No functional change is expected.
>
> Signed-off-by: Wei Yang <richard.weiyang@...il.com>
> ---
>  mm/swapfile.c | 4 ----
>  1 file changed, 4 deletions(-)
>
> diff --git a/mm/swapfile.c b/mm/swapfile.c
> index 3aae700f9931..07b0bc095411 100644
> --- a/mm/swapfile.c
> +++ b/mm/swapfile.c
> @@ -629,10 +629,6 @@ static bool scan_swap_map_try_ssd_cluster(struct swap_info_struct *si,
>  	tmp = cluster->next;
>  	max = min_t(unsigned long, si->max,
>  		    (cluster_next(&cluster->index) + 1) * SWAPFILE_CLUSTER);
> -	if (tmp >= max) {
> -		cluster_set_null(&cluster->index);
> -		goto new_cluster;
> -	}

The code is to avoid to acquire the cluster lock unnecessarily.  So I think
we should keep this.

Best Regards,
Huang, Ying

>  	ci = lock_cluster(si, tmp);
>  	while (tmp < max) {
>  		if (!si->swap_map[tmp])