linux-kernel - Re: [PATCH 1/2] mm: use kvzalloc for swap_info

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Date:   Mon, 05 Nov 2018 08:50:04 +0800
From:   "Huang\, Ying" <ying.huang@...el.com>
To:     Vasily Averin <vvs@...tuozzo.com>
Cc:     <linux-mm@...ck.org>, Andrew Morton <akpm@...ux-foundation.org>,
        <linux-kernel@...r.kernel.org>, "Aaron Lu" <aaron.lu@...el.com>
Subject: Re: [PATCH 1/2] mm: use kvzalloc for swap_info_struct allocation

Vasily Averin <vvs@...tuozzo.com> writes:

> commit a2468cc9bfdf ("swap: choose swap device according to numa node")
> increased size of swap_info_struct up to 44 Kbytes, now it requires
> 4th order page.

Why swap_info_struct could be so large?  Because MAX_NUMNODES could be
thousands so that 'avail_lists' field could be tens KB?  If so, I think
it's fair to use kvzalloc().  Can you add one line comment?  Because
struct swap_info_struct is quite small in default configuration.

Best Regards,
Huang, Ying

> Switch to kvzmalloc allows to avoid unexpected allocation failures.
>
> Signed-off-by: Vasily Averin <vvs@...tuozzo.com>
> ---
>  mm/swapfile.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/mm/swapfile.c b/mm/swapfile.c
> index 644f746e167a..8688ae65ef58 100644
> --- a/mm/swapfile.c
> +++ b/mm/swapfile.c
> @@ -2813,7 +2813,7 @@ static struct swap_info_struct *alloc_swap_info(void)
>  	unsigned int type;
>  	int i;
>  
> -	p = kzalloc(sizeof(*p), GFP_KERNEL);
> +	p = kvzalloc(sizeof(*p), GFP_KERNEL);
>  	if (!p)
>  		return ERR_PTR(-ENOMEM);
>  
> @@ -2824,7 +2824,7 @@ static struct swap_info_struct *alloc_swap_info(void)
>  	}
>  	if (type >= MAX_SWAPFILES) {
>  		spin_unlock(&swap_lock);
> -		kfree(p);
> +		kvfree(p);
>  		return ERR_PTR(-EPERM);
>  	}
>  	if (type >= nr_swapfiles) {
> @@ -2838,7 +2838,7 @@ static struct swap_info_struct *alloc_swap_info(void)
>  		smp_wmb();
>  		nr_swapfiles++;
>  	} else {
> -		kfree(p);
> +		kvfree(p);
>  		p = swap_info[type];
>  		/*
>  		 * Do not memset this entry: a racing procfs swap_next()