Re: [PATCH nf,v3] netfilter: nf_tables: coalesce multiple notifications into one skbuff

[Phil Sutter <phil@nwl.cc>]

On Wed, Sep 02, 2020 at 06:37:43PM +0200, Pablo Neira Ayuso wrote:
> On x86_64, each notification results in one skbuff allocation which
> consumes at least 768 bytes due to the skbuff overhead.
> 
> This patch coalesces several notifications into one single skbuff, so
> each notification consumes at least ~211 bytes, that ~3.5 times less
> memory consumption. As a result, this is reducing the chances to exhaust
> the netlink socket receive buffer.
> 
> Rule of thumb is that each notification batch only contains netlink
> messages whose report flag is the same, nfnetlink_send() requires this
> to do appropriately delivery to userspace, either via unicast (echo
> mode) or multicast (monitor mode).
> 
> The skbuff control buffer is used to annotate the report flag for later
> handling at the new coalescing routine.
> 
> The batch skbuff notification size is NLMSG_GOODSIZE, using a larger
> skbuff would allow for more socket receiver buffer savings (to amortize
> the cost of the skbuff even more), however, going over that size might
> break userspace applications, so let's be conservative and stick to
> NLMSG_GOODSIZE.
> 
> Reported-by: Phil Sutter <phil@nwl.cc>
> Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

Acked-by: Phil Sutter <phil@nwl.cc>

Thanks, Phil