From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753592Ab3KLRpk (ORCPT ); Tue, 12 Nov 2013 12:45:40 -0500 Received: from mga11.intel.com ([192.55.52.93]:36902 "EHLO mga11.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752664Ab3KLRpg (ORCPT ); Tue, 12 Nov 2013 12:45:36 -0500 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.93,686,1378882800"; d="scan'208";a="432201971" Date: Tue, 12 Nov 2013 09:45:01 -0800 From: Greg Rose To: Jason Wang CC: , , , , Subject: Re: [PATCH net 2/2] macvtap: limit head length of skb allocated Message-ID: <20131112094501.0000358d@unknown> In-Reply-To: <1384250577-20330-2-git-send-email-jasowang@redhat.com> References: <1384250577-20330-1-git-send-email-jasowang@redhat.com> <1384250577-20330-2-git-send-email-jasowang@redhat.com> Organization: Intel X-Mailer: Claws Mail 3.7.8cvs47 (GTK+ 2.16.6; i586-pc-mingw32msvc) MIME-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit X-Originating-IP: [10.22.254.140] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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