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Date:   Thu, 21 May 2020 09:35:32 -0400
From:   Daniel Jordan <daniel.m.jordan@oracle.com>
To:     Huang Ying <ying.huang@intel.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org,
        Daniel Jordan <daniel.m.jordan@oracle.com>,
        Michal Hocko <mhocko@suse.com>,
        Minchan Kim <minchan@kernel.org>,
        Tim Chen <tim.c.chen@linux.intel.com>,
        Hugh Dickins <hughd@google.com>
Subject: Re: [PATCH -V2] swap: Reduce lock contention on swap cache from swap
 slots allocation
Message-ID: <20200521133532.psckytr456eevs5j@ca-dmjordan1.us.oracle.com>
References: <20200520031502.175659-1-ying.huang@intel.com>
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On Wed, May 20, 2020 at 11:15:02AM +0800, Huang Ying wrote:
> @@ -2827,6 +2865,11 @@ static struct swap_info_struct *alloc_swap_info(void)
>  	p = kvzalloc(struct_size(p, avail_lists, nr_node_ids), GFP_KERNEL);
>  	if (!p)
>  		return ERR_PTR(-ENOMEM);
> +	p->cluster_next_cpu = alloc_percpu(unsigned int);
> +	if (!p->cluster_next_cpu) {
> +		kvfree(p);
> +		return ERR_PTR(-ENOMEM);
> +	}

There should be free_percpu()s at two places after this, but I think the
allocation really belongs right...

> @@ -3202,7 +3245,10 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
>  		 * select a random position to start with to help wear leveling
>  		 * SSD
>  		 */
> -		p->cluster_next = 1 + prandom_u32_max(p->highest_bit);

...here because then it's only allocated when it's actually used.

> +		for_each_possible_cpu(cpu) {
> +			per_cpu(*p->cluster_next_cpu, cpu) =
> +				1 + prandom_u32_max(p->highest_bit);
> +		}
>  		nr_cluster = DIV_ROUND_UP(maxpages, SWAPFILE_CLUSTER);
>  
>  		cluster_info = kvcalloc(nr_cluster, sizeof(*cluster_info),
> -- 
> 2.26.2
> 
>