From f42157cb568c1eb02eca7df4da67553a9edae24a Mon Sep 17 00:00:00 2001 From: Rusty Russell Date: Fri, 15 Aug 2008 15:15:10 -0700 Subject: [PATCH] tun: fallback if skb_alloc() fails on big packets skb_alloc produces linear packets (using kmalloc()). That can fail, so should we fall back to making paged skbs. My original version of this patch always allocate paged skbs for big packets. But that made performance drop from 8.4 seconds to 8.8 seconds on 1G lguest->Host TCP xmit. So now we only do that as a fallback. Signed-off-by: Rusty Russell Acked-by: Max Krasnyansky Signed-off-by: David S. Miller --- drivers/net/tun.c | 66 ++++++++++++++++++++++++++++++++++++++++++++--- 1 file changed, 62 insertions(+), 4 deletions(-) diff --git a/drivers/net/tun.c b/drivers/net/tun.c index 95931a5a98..6daea0c918 100644 --- a/drivers/net/tun.c +++ b/drivers/net/tun.c @@ -358,6 +358,66 @@ static unsigned int tun_chr_poll(struct file *file, poll_table * wait) return mask; } +/* prepad is the amount to reserve at front. len is length after that. + * linear is a hint as to how much to copy (usually headers). */ +static struct sk_buff *tun_alloc_skb(size_t prepad, size_t len, size_t linear, + gfp_t gfp) +{ + struct sk_buff *skb; + unsigned int i; + + skb = alloc_skb(prepad + len, gfp|__GFP_NOWARN); + if (skb) { + skb_reserve(skb, prepad); + skb_put(skb, len); + return skb; + } + + /* Under a page? Don't bother with paged skb. */ + if (prepad + len < PAGE_SIZE) + return NULL; + + /* Start with a normal skb, and add pages. */ + skb = alloc_skb(prepad + linear, gfp); + if (!skb) + return NULL; + + skb_reserve(skb, prepad); + skb_put(skb, linear); + + len -= linear; + + for (i = 0; i < MAX_SKB_FRAGS; i++) { + skb_frag_t *f = &skb_shinfo(skb)->frags[i]; + + f->page = alloc_page(gfp|__GFP_ZERO); + if (!f->page) + break; + + f->page_offset = 0; + f->size = PAGE_SIZE; + + skb->data_len += PAGE_SIZE; + skb->len += PAGE_SIZE; + skb->truesize += PAGE_SIZE; + skb_shinfo(skb)->nr_frags++; + + if (len < PAGE_SIZE) { + len = 0; + break; + } + len -= PAGE_SIZE; + } + + /* Too large, or alloc fail? */ + if (unlikely(len)) { + kfree_skb(skb); + skb = NULL; + } + + return skb; +} + /* Get packet from user space buffer */ static __inline__ ssize_t tun_get_user(struct tun_struct *tun, struct iovec *iv, size_t count) { @@ -391,14 +451,12 @@ static __inline__ ssize_t tun_get_user(struct tun_struct *tun, struct iovec *iv, return -EINVAL; } - if (!(skb = alloc_skb(len + align, GFP_KERNEL))) { + if (!(skb = tun_alloc_skb(align, len, gso.hdr_len, GFP_KERNEL))) { tun->dev->stats.rx_dropped++; return -ENOMEM; } - if (align) - skb_reserve(skb, align); - if (memcpy_fromiovec(skb_put(skb, len), iv, len)) { + if (skb_copy_datagram_from_iovec(skb, 0, iv, len)) { tun->dev->stats.rx_dropped++; kfree_skb(skb); return -EFAULT; -- 2.39.5