Re: [PATCHv3 net-next] netlink: allow large data transfers from user-space

[David Miller <davem@davemloft.net>]

From: pablo@netfilter.org
Date: Mon,  3 Jun 2013 21:46:28 +0200

> From: Pablo Neira Ayuso <pablo@netfilter.org>
> 
> I can hit ENOBUFS in the sendmsg() path with a large batch that is
> composed of many netlink messages. Here that limit is 8 MBytes of
> skbuff data area as kmalloc does not manage to get more than that.
> 
> While discussing atomic rule-set for nftables with Patrick McHardy,
> we decided to put all rule-set updates that need to be applied
> atomically in one single batch to simplify the existing approach.
> However, as explained above, the existing netlink code limits us
> to a maximum of ~20000 rules that fit in one single batch without
> hitting ENOBUFS. iptables does not have such limitation as it is
> using vmalloc.
> 
> This patch adds netlink_alloc_large_skb() which is only used in
> the netlink_sendmsg() path. It uses alloc_skb if the memory
> requested is <= one memory page, that should be the common case
> for most subsystems, else vmalloc for higher memory allocations.
> 
> Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

Ok since this is confined to netlink let's give this a shot.