Messages in this thread | | | Date | Wed, 09 Aug 2023 09:18:22 -0400 | From | Willem de Bruijn <> | Subject | RE: [PATCH v3] tun: avoid high-order page allocation for packet header |
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Tahsin Erdogan wrote: > When GSO is not enabled
Not GSO, but gso.hdr_len, which is a feature of IFF_VNET_HDR.
VIRTIO_NET_HDR_GSO_* does not need to be enabled to use the header length field.
> and a packet is transmitted via writev(), all > payload is treated as header which requires a contiguous memory allocation. > This allocation request is harder to satisfy, and may even fail if there is > enough fragmentation. > > Note that sendmsg() code path limits the linear copy length, so this change > makes writev() and sendmsg() more consistent.
This is not specific to writev(), equally to more common write().
Tun sendmsg is a special case, only used by vhost-net from inside the kernel. Arguably consistency with packet_snd/packet_alloc_skb would be more important. That said, this makes sense to me. I assume your configuring a device with very large MTU?
> Signed-off-by: Tahsin Erdogan <trdgn@amazon.com> > --- > v3: rebase to latest net-next > v2: replace linear == 0 with !linear > v1: https://lore.kernel.org/all/20230726030936.1587269-1-trdgn@amazon.com/ > drivers/net/tun.c | 5 ++++- > 1 file changed, 4 insertions(+), 1 deletion(-) > > diff --git a/drivers/net/tun.c b/drivers/net/tun.c > index 5beb6b5dd7e5..53d19c958a20 100644 > --- a/drivers/net/tun.c > +++ b/drivers/net/tun.c > @@ -1523,7 +1523,7 @@ static struct sk_buff *tun_alloc_skb(struct tun_file *tfile, > int err; > > /* Under a page? Don't bother with paged skb. */ > - if (prepad + len < PAGE_SIZE || !linear) > + if (prepad + len < PAGE_SIZE) > linear = len; > > if (len - linear > MAX_SKB_FRAGS * (PAGE_SIZE << PAGE_ALLOC_COSTLY_ORDER)) > @@ -1913,6 +1913,9 @@ static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile, > */ > zerocopy = false; > } else { > + if (!linear) > + linear = min_t(size_t, good_linear, copylen); > + > skb = tun_alloc_skb(tfile, align, copylen, linear, > noblock); > } > -- > 2.41.0 >
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