From: Eric Dumazet <[email protected]> Date: Wed, 19 Sep 2012 18:56:01 +0200
> From: Eric Dumazet <[email protected]> > > We currently use a per socket page reserve for tcp_sendmsg() operations. > > This page is used to build fragments for skbs. > > Its done to increase probability of coalescing small write() into > single segments in skbs still in write queue (not yet sent) > > But it wastes a lot of memory for applications handling many mostly > idle sockets, since each socket holds one page in sk->sk_sndmsg_page > > Its also quite inefficient to build TSO packets of 64KB, because we need > about 16 pages per skb on arches where PAGE_SIZE = 4096, so we hit > page allocator more than wanted. > > This patch switches this frag allocator from socket to task structure, > and uses bigger pages. > > (up to 32768 bytes per frag, thats order-3 pages on x86) > > This increases TCP stream performance by 20% on loopback device, > but also benefits on other network devices, since 8x less frags are > mapped on transmit and unmapped on tx completion. > > Its possible some TSO enabled hardware cant cope with bigger fragments, > but their ndo_start_xmit() should already handle this, splitting a > fragment in sub fragments, since some arches have PAGE_SIZE=65536 > > Successfully tested on various ethernet devices. > (ixgbe, igb, bnx2x, tg3, mellanox mlx4) > > Followup patches can use this infrastructure in two other spots > and get rid of the socket sk_sndmsg_page. > > Open for discussion : Should we fallback to smaller pages > if order-3 page allocations fail ? > > Signed-off-by: Eric Dumazet <[email protected]> I like this a lot and I look forward to your upcoming changes to convert the other two sk_sndmsg_page users as well, but I can't apply this to net-next just yet. The question on fallback is a good one and something we have to resolve before applying this. Note in particular that sk_allocation can be set to just about anything, and this also has potential interaction issues with SOCK_MEMALLOC. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
