On Fri, 2012-10-19 at 09:03 +0900, JoonSoo Kim wrote: > Hello, Eric. > Thank you very much for a kind comment about my question. > I have one more question related to network subsystem. > Please let me know what I misunderstand. > > 2012/10/14 Eric Dumazet <eric.dumazet@xxxxxxxxx>: > > In latest kernels, skb->head no longer use kmalloc()/kfree(), so SLAB vs > > SLUB is less a concern for network loads. > > > > In 3.7, (commit 69b08f62e17) we use fragments of order-3 pages to > > populate skb->head. > > You mentioned that in latest kernel skb->head no longer use kmalloc()/kfree(). I hadnt the time to fully explain what was going on, only to give some general ideas/hints. Only incoming skbs, delivered by NIC are built this way. I plan to extend this to some kind of frames, for example TCP ACK. (They have a short life, so using __netdev_alloc_frag makes sense) But when an application does a tcp_sendmsg() we use GFP_KERNEL allocations and thus still use kmalloc(). > But, why result of David's "netperf RR" test on v3.6 is differentiated > by choosing the allocator? Because outgoing skb are still using a kmalloc() for their skb->head RR sends one frame, receives one frame for each transaction. So with 3.5, each RR transaction using a NIC needs 3 kmalloc() instead of 4 for previous kernels. Note that loopback traffic is different, since we do 2 kmalloc() per transaction, and there is no difference on 3.5 for this kind of network load. > As far as I know, __netdev_alloc_frag may be introduced in v3.5, so > I'm just confused. > Does this test use __netdev_alloc_skb with "__GFP_WAIT | GFP_DMA"? > > Does normal workload for network use __netdev_alloc_skb with > "__GFP_WAIT | GFP_DMA"? > Not especially. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>