From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jason Wang Subject: Re: [PATCH net 2/2] macvtap: limit head length of skb allocated Date: Wed, 13 Nov 2013 13:58:01 +0800 Message-ID: <528314E9.1020000@redhat.com> References: <1384250577-20330-1-git-send-email-jasowang@redhat.com> <1384250577-20330-2-git-send-email-jasowang@redhat.com> <20131112094501.0000358d@unknown> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: davem@davemloft.net, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, mst@redhat.com, stefanha@redhat.com To: Greg Rose Return-path: In-Reply-To: <20131112094501.0000358d@unknown> Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On 11/13/2013 01:45 AM, Greg Rose wrote: > On Tue, 12 Nov 2013 18:02:57 +0800 > Jason Wang wrote: > >> We currently use hdr_len as a hint of head length which is advertised >> by guest. But when guest advertise a very big value, it can lead to >> an 64K+ allocating of kmalloc() which has a very high possibility of >> failure when host memory is fragmented or under heavy stress. The >> huge hdr_len also reduce the effect of zerocopy or even disable if a >> gso skb is linearized in guest. >> >> To solves those issues, this patch introduces an upper limit >> (PAGE_SIZE) of the head, which guarantees an order 0 allocation each >> time. >> >> Cc: Stefan Hajnoczi >> Cc: Michael S. Tsirkin >> Signed-off-by: Jason Wang >> --- >> The patch was needed for stable. >> --- >> drivers/net/macvtap.c | 5 +++++ >> 1 file changed, 5 insertions(+) >> >> diff --git a/drivers/net/macvtap.c b/drivers/net/macvtap.c >> index 9dccb1e..7ee6f9d 100644 >> --- a/drivers/net/macvtap.c >> +++ b/drivers/net/macvtap.c >> @@ -523,6 +523,11 @@ static inline struct sk_buff >> *macvtap_alloc_skb(struct sock *sk, size_t prepad, int noblock, int >> *err) { >> struct sk_buff *skb; >> + int good_linear = SKB_MAX_HEAD(prepad); >> + >> + /* Don't use huge linear part */ >> + if (linear > good_linear) >> + linear = good_linear; >> >> /* Under a page? Don't bother with paged skb. */ >> if (prepad + len < PAGE_SIZE || !linear) > I see no problem with this or the tuntap patch except that in both > cases kernel coding style would prefer that you align the local > variable declarations in a reverse pyramid, longest at the beginning, > shortest at the end. > > - Greg Sure, will do it in V2. Thanks > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/