> -----Original Message----- > From: David Miller [mailto:da...@davemloft.net] > Sent: Friday, February 16, 2018 21:33 > To: Jon Maloy <jon.ma...@ericsson.com> > Cc: netdev@vger.kernel.org; Mohan Krishna Ghanta Krishnamurthy > <mohan.krishna.ghanta.krishnamur...@ericsson.com>; Tung Quang Nguyen > <tung.q.ngu...@dektech.com.au>; Hoang Huu Le > <hoang.h...@dektech.com.au>; Canh Duc Luu > <canh.d....@dektech.com.au>; Ying Xue <ying....@windriver.com>; tipc- > discuss...@lists.sourceforge.net > Subject: Re: [net-next v2 1/1] tipc: avoid unnecessary copying of bundled > messages > > From: Jon Maloy <jon.ma...@ericsson.com> > Date: Thu, 15 Feb 2018 14:14:37 +0100 > > > A received sk buffer may contain dozens of smaller 'bundled' messages > > which after extraction go each in their own direction. > > > > Unfortunately, when we extract those messages using skb_clone() each > > of the extracted buffers inherit the truesize value of the original > > buffer. Apart from causing massive overaccounting of the base buffer's > > memory, this often causes tipc_msg_validate() to come to the false > > conclusion that the ratio truesize/datasize > 4, and perform an > > unnecessary copying of the extracted buffer. > > > > We now fix this problem by explicitly correcting the truesize value of > > the buffer clones to be the truesize of the clone itself plus a > > calculated fraction of the base buffer's overhead. This change > > eliminates the overaccounting and at least mitigates the occurrence of > > unnecessary buffer copying. > > > > Reported-by: Hoang Le <hoang.h...@dektek.com.au> > > Acked-by: Ying Xue <ying....@windriver.com> > > Signed-off-by: Jon Maloy <jon.ma...@ericsson.com> > > As I explained in my previous two emails, I don't think this method of > accounting is appropriate. > > All of your clones must use the same skb->truesize as the original SKB > because each and every one of them keeps the full buffer from being > liberated until they are released.
I understand what you are saying, although I am not happy with its consequences in this case. I guess I will just leave it the way it is until I can come up with something smarter. ///jon
