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d3836f21b0
skb->head is currently allocated from kmalloc(). This is convenient but has the drawback the data cannot be converted to a page fragment if needed. We have three spots were it hurts : 1) GRO aggregation When a linear skb must be appended to another skb, GRO uses the frag_list fallback, very inefficient since we keep all struct sk_buff around. So drivers enabling GRO but delivering linear skbs to network stack aren't enabling full GRO power. 2) splice(socket -> pipe). We must copy the linear part to a page fragment. This kind of defeats splice() purpose (zero copy claim) 3) TCP coalescing. Recently introduced, this permits to group several contiguous segments into a single skb. This shortens queue lengths and save kernel memory, and greatly reduce probabilities of TCP collapses. This coalescing doesnt work on linear skbs (or we would need to copy data, this would be too slow) Given all these issues, the following patch introduces the possibility of having skb->head be a fragment in itself. We use a new skb flag, skb->head_frag to carry this information. build_skb() is changed to accept a frag_size argument. Drivers willing to provide a page fragment instead of kmalloc() data will set a non zero value, set to the fragment size. Then, on situations we need to convert the skb head to a frag in itself, we can check if skb->head_frag is set and avoid the copies or various fallbacks we have. This means drivers currently using frags could be updated to avoid the current skb->head allocation and reduce their memory footprint (aka skb truesize). (thats 512 or 1024 bytes saved per skb). This also makes bpf/netfilter faster since the 'first frag' will be part of skb linear part, no need to copy data. Signed-off-by: Eric Dumazet <edumazet@google.com> Cc: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi> Cc: Herbert Xu <herbert@gondor.apana.org.au> Cc: Maciej Żenczykowski <maze@google.com> Cc: Neal Cardwell <ncardwell@google.com> Cc: Tom Herbert <therbert@google.com> Cc: Jeff Kirsher <jeffrey.t.kirsher@intel.com> Cc: Ben Hutchings <bhutchings@solarflare.com> Cc: Matt Carlson <mcarlson@broadcom.com> Cc: Michael Chan <mchan@broadcom.com> Signed-off-by: David S. Miller <davem@davemloft.net> |
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| 9p | ||
| 802 | ||
| 8021q | ||
| appletalk | ||
| atm | ||
| ax25 | ||
| batman-adv | ||
| bluetooth | ||
| bridge | ||
| caif | ||
| can | ||
| ceph | ||
| core | ||
| dcb | ||
| dccp | ||
| decnet | ||
| dns_resolver | ||
| dsa | ||
| econet | ||
| ethernet | ||
| ieee802154 | ||
| ipv4 | ||
| ipv6 | ||
| ipx | ||
| irda | ||
| iucv | ||
| key | ||
| l2tp | ||
| lapb | ||
| llc | ||
| mac80211 | ||
| netfilter | ||
| netlabel | ||
| netlink | ||
| netrom | ||
| nfc | ||
| openvswitch | ||
| packet | ||
| phonet | ||
| rds | ||
| rfkill | ||
| rose | ||
| rxrpc | ||
| sched | ||
| sctp | ||
| sunrpc | ||
| tipc | ||
| unix | ||
| wanrouter | ||
| wimax | ||
| wireless | ||
| x25 | ||
| xfrm | ||
| compat.c | ||
| Kconfig | ||
| Makefile | ||
| nonet.c | ||
| socket.c | ||
| sysctl_net.c | ||