netdev - Re: [PATCH net-next 1/7] ipv4: nexthop: Reduce allocation size of 'struct nh

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Message-ID: <88977c63-b4f7-991f-e0a7-b0ee420ba617@gmail.com>
Date:   Wed, 26 Aug 2020 13:06:34 -0600
From:   David Ahern <dsahern@...il.com>
To:     Ido Schimmel <idosch@...sch.org>, netdev@...r.kernel.org
Cc:     davem@...emloft.net, kuba@...nel.org, mlxsw@...dia.com,
        Ido Schimmel <idosch@...dia.com>
Subject: Re: [PATCH net-next 1/7] ipv4: nexthop: Reduce allocation size of
 'struct nh_group'

On 8/26/20 10:48 AM, Ido Schimmel wrote:
> From: Ido Schimmel <idosch@...dia.com>
> 
> The struct looks as follows:
> 
> struct nh_group {
> 	struct nh_group		*spare; /* spare group for removals */
> 	u16			num_nh;
> 	bool			mpath;
> 	bool			fdb_nh;
> 	bool			has_v4;
> 	struct nh_grp_entry	nh_entries[];
> };
> 
> But its offset within 'struct nexthop' is also taken into account to
> determine the allocation size.

must be a leftover from initial versions. Thanks for catching this.

> 
> Instead, use struct_size() to allocate only the required number of
> bytes.
> 
> Signed-off-by: Ido Schimmel <idosch@...dia.com>
> ---
>  net/ipv4/nexthop.c | 5 +----
>  1 file changed, 1 insertion(+), 4 deletions(-)
> 
> diff --git a/net/ipv4/nexthop.c b/net/ipv4/nexthop.c
> index 134e92382275..d13730ff9aeb 100644
> --- a/net/ipv4/nexthop.c
> +++ b/net/ipv4/nexthop.c
> @@ -133,12 +133,9 @@ static struct nexthop *nexthop_alloc(void)
>  
>  static struct nh_group *nexthop_grp_alloc(u16 num_nh)
>  {
> -	size_t sz = offsetof(struct nexthop, nh_grp)
> -		    + sizeof(struct nh_group)
> -		    + sizeof(struct nh_grp_entry) * num_nh;
>  	struct nh_group *nhg;
>  
> -	nhg = kzalloc(sz, GFP_KERNEL);
> +	nhg = kzalloc(struct_size(nhg, nh_entries, num_nh), GFP_KERNEL);
>  	if (nhg)
>  		nhg->num_nh = num_nh;
>  
> 

Reviewed-by: David Ahern <dsahern@...il.com>