On Wed, Sep 02, 2020 at 06:39:34PM +0200, Phil Sutter wrote: > 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@xxxxxx> > > Signed-off-by: Pablo Neira Ayuso <pablo@xxxxxxxxxxxxx> > > Acked-by: Phil Sutter <phil@xxxxxx> Thanks, I'll place this into nf.git BTW, I assume this mitigates the problem that Eric reported? Is it not so easy to trigger the problem after this patch? I forgot to say, probably it would be good to monitor /proc/net/netlink to catch how busy the socket receive buffer is getting with your firewalld ruleset. Thanks.
