> -----Original Message----- > From: David Laight [mailto:david.lai...@aculab.com] > Sent: Monday, February 19, 2018 14:30 > To: Jon Maloy <jon.ma...@ericsson.com> > Cc: firstname.lastname@example.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. > > Have you actually checked that copying the data when you extract the > messages isn't faster than cloning and trying to avoid the copy? > Copying at the point is probably cheaper because it leads to a simpler > message structure.
Yes, that is probably what I'll end up doing, if copying is unavoidable anyway. ///jon > > David