linux-kernel - Re: [PATCH 2/3] mm: use vmalloc_array and vcalloc for array allocations

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Date:   Tue, 8 Mar 2022 14:49:01 +0100
From:   Michal Hocko <mhocko@...e.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        Michael Ellerman <mpe@...erman.id.au>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Dennis Zhou <dennis@...nel.org>, Tejun Heo <tj@...nel.org>,
        Christoph Lameter <cl@...ux.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>, linux-mm@...ck.org,
        cgroups@...r.kernel.org
Subject: Re: [PATCH 2/3] mm: use vmalloc_array and vcalloc for array
 allocations

On Tue 08-03-22 05:59:17, Paolo Bonzini wrote:
> Instead of using array_size or just a multiply, use a function that
> takes care of both the multiplication and the overflow checks.
> 
> Cc: linux-mm@...ck.org
> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>

Acked-by: Michal Hocko <mhocko@...e.com>

The resulting code is easier to read indeed.

> ---
>  mm/percpu-stats.c | 2 +-
>  mm/swap_cgroup.c  | 4 +---
>  2 files changed, 2 insertions(+), 4 deletions(-)
> 
> diff --git a/mm/percpu-stats.c b/mm/percpu-stats.c
> index c6bd092ff7a3..e71651cda2de 100644
> --- a/mm/percpu-stats.c
> +++ b/mm/percpu-stats.c
> @@ -144,7 +144,7 @@ static int percpu_stats_show(struct seq_file *m, void *v)
>  	spin_unlock_irq(&pcpu_lock);
>  
>  	/* there can be at most this many free and allocated fragments */
> -	buffer = vmalloc(array_size(sizeof(int), (2 * max_nr_alloc + 1)));
> +	buffer = vmalloc_array(2 * max_nr_alloc + 1, sizeof(int));
>  	if (!buffer)
>  		return -ENOMEM;
>  
> diff --git a/mm/swap_cgroup.c b/mm/swap_cgroup.c
> index 7f34343c075a..5a9442979a18 100644
> --- a/mm/swap_cgroup.c
> +++ b/mm/swap_cgroup.c
> @@ -167,14 +167,12 @@ unsigned short lookup_swap_cgroup_id(swp_entry_t ent)
>  int swap_cgroup_swapon(int type, unsigned long max_pages)
>  {
>  	void *array;
> -	unsigned long array_size;
>  	unsigned long length;
>  	struct swap_cgroup_ctrl *ctrl;
>  
>  	length = DIV_ROUND_UP(max_pages, SC_PER_PAGE);
> -	array_size = length * sizeof(void *);
>  
> -	array = vzalloc(array_size);
> +	array = vcalloc(length, sizeof(void *));
>  	if (!array)
>  		goto nomem;
>  
> -- 
> 2.31.1
> 
> 

-- 
Michal Hocko
SUSE Labs