Attachment 299793 Details for Bug 439923 – Avoid multi-page allocations in IP fragmentation

[patch] Avoid multi-page allocations in IP fragmentation

linux-2.6.9-zab_mtu_u6_2.patch (text/plain), 2.90 KB, created by Greg Marsden on 2008-03-31 23:47:08 UTC

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Creator: Greg Marsden

Created: 2008-03-31 23:47:08 UTC

Size: 2.90 KB

patch

obsolete

>From: Olaf Kirch <olaf.kirch@oracle.com>
>Subject: Avoid multi-page allocations in IP fragmentation
>
>This patch is based on a patch by Zach Brown. The idea is to avoid
>multi-order allocations in the fragment handling code, because that
>will fail on heavily loaded machines where memory tends to become
>rather fragmented. Original posting can be found here:
>
>http://marc.info/?l=linux-netdev&m=114425947024500&w=2
>
>This modified patch addresses a problem encountered on ppc - the
>original patch caused skb_shared_info to become unaligned, which causes
>crashes on ppc (see bug #6140918). The first iteration introduced a new
>problem (described in bug #6845794).
>
>Olaf Kirch <olaf.kirch@oracle.com>
>---
> net/ipv4/ip_output.c |   40 +++++++++++++++++++++++++++-------------
> 1 file changed, 27 insertions(+), 13 deletions(-)
>
>Index: linux-2.6.9/net/ipv4/ip_output.c
>===================================================================
>--- linux-2.6.9.orig/net/ipv4/ip_output.c
>+++ linux-2.6.9/net/ipv4/ip_output.c
>@@ -824,32 +824,46 @@ alloc_new_skb:
> 			datalen = length + fraggap;
> 			if (datalen > mtu - fragheaderlen)
> 				datalen = maxfraglen - fragheaderlen;
>-			fraglen = datalen + fragheaderlen;
> 
>-			if ((flags & MSG_MORE) && 
>-			    !(rt->u.dst.dev->features&NETIF_F_SG))
>-				alloclen = mtu;
>-			else
>-				alloclen = datalen + fragheaderlen;
>+			alloclen = fragheaderlen + hh_len + 15;
> 
> 			/* The last fragment gets additional space at tail.
> 			 * Note, with MSG_MORE we overallocate on fragments,
> 			 * because we have no idea what fragment will be
> 			 * the last.
> 			 */
>-			if (datalen == length)
>+			if (datalen == length + fraggap)
> 				alloclen += rt->u.dst.trailer_len;
>+			if ((rt->u.dst.dev->features&NETIF_F_SG) &&
>+			    datalen > SKB_MAX_ORDER(alloclen, 0)) {
>+				/* If we added a trailer, we have to remove
>+				 * it again.
>+				 * However, this may actually increase
>+				 * SKB_MAX_ORDER(alloclen) signficantly -
>+				 * ie by SMP_CACHE_BYTES - so we need to make
>+				 * sure we don't accidentally increase datalen.
>+				 */
>+				if (datalen == length + fraggap)
>+					alloclen -= rt->u.dst.trailer_len;
>+				datalen = min_t(unsigned int, datalen,
>+						SKB_MAX_ORDER(alloclen, 0));
>+			}
>+
>+			fraglen = datalen + fragheaderlen;
>+
>+			if ((flags & MSG_MORE) &&
>+			   !(rt->u.dst.dev->features&NETIF_F_SG))
>+			       alloclen += mtu - fragheaderlen;
>+			else
>+			       alloclen += datalen;
> 
> 			if (transhdrlen) {
>-				skb = sock_alloc_send_skb(sk, 
>-						alloclen + hh_len + 15,
>+				skb = sock_alloc_send_skb(sk, alloclen,
> 						(flags & MSG_DONTWAIT), &err);
> 			} else {
> 				skb = NULL;
>-				if (atomic_read(&sk->sk_wmem_alloc) <=
>-				    2 * sk->sk_sndbuf)
>-					skb = sock_wmalloc(sk, 
>-							   alloclen + hh_len + 15, 1,
>+				if (atomic_read(&sk->sk_wmem_alloc) <= 2 * sk->sk_sndbuf)
>+				       skb = sock_wmalloc(sk, alloclen, 1,
> 							   sk->sk_allocation);
> 				if (unlikely(skb == NULL))
> 					err = -ENOBUFS;

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Attachments on bug 439923: 299793