linux-kernel - Re: [PATCH 2/8] mm/swap: Add cluster lock

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Date:   Wed, 28 Sep 2016 16:42:21 +0800
From:   "Hillf Danton" <hillf.zj@...baba-inc.com>
To:     <tim.c.chen@...ux.intel.com>,
        "'Andrew Morton'" <akpm@...ux-foundation.org>
Cc:     <dave.hansen@...el.com>, <andi.kleen@...el.com>,
        <aaron.lu@...el.com>, <linux-mm@...ck.org>,
        <linux-kernel@...r.kernel.org>,
        "'Huang Ying'" <ying.huang@...el.com>,
        "'Hugh Dickins'" <hughd@...gle.com>,
        "'Shaohua Li'" <shli@...nel.org>,
        "'Minchan Kim'" <minchan@...nel.org>,
        "'Rik van Riel'" <riel@...hat.com>,
        "'Andrea Arcangeli'" <aarcange@...hat.com>,
        "'Kirill A . Shutemov'" <kirill.shutemov@...ux.intel.com>,
        "'Vladimir Davydov'" <vdavydov@...tuozzo.com>,
        "'Johannes Weiner'" <hannes@...xchg.org>,
        "'Michal Hocko'" <mhocko@...nel.org>
Subject: Re: [PATCH 2/8] mm/swap: Add cluster lock

On Wednesday, September 28, 2016 1:18 AM Tim Chen wrote
> 
> @@ -447,8 +505,9 @@ static void scan_swap_map_try_ssd_cluster(struct swap_info_struct *si,
>  	unsigned long *offset, unsigned long *scan_base)
>  {
>  	struct percpu_cluster *cluster;
> +	struct swap_cluster_info *ci;
>  	bool found_free;
> -	unsigned long tmp;
> +	unsigned long tmp, max;
> 
>  new_cluster:
>  	cluster = this_cpu_ptr(si->percpu_cluster);
> @@ -476,14 +535,21 @@ new_cluster:
>  	 * check if there is still free entry in the cluster
>  	 */
>  	tmp = cluster->next;
> -	while (tmp < si->max && tmp < (cluster_next(&cluster->index) + 1) *
> -	       SWAPFILE_CLUSTER) {

Currently tmp is checked to be less than both values.

> +	max = max_t(unsigned long, si->max,
> +		    (cluster_next(&cluster->index) + 1) * SWAPFILE_CLUSTER);
> +	if (tmp >= max) {
> +		cluster_set_null(&cluster->index);
> +		goto new_cluster;
> +	}
> +	ci = lock_cluster(si, tmp);
> +	while (tmp < max) {

In this work tmp is checked to be less than the max value.
Semantic change hoped?

>  		if (!si->swap_map[tmp]) {
>  			found_free = true;
>  			break;
>  		}
>  		tmp++;
>  	}
> +	unlock_cluster(ci);
>  	if (!found_free) {
>  		cluster_set_null(&cluster->index);
>  		goto new_cluster;
> 
thanks
Hillf