Do not top-post on netdev, please.
On Sat, 2017-05-06 at 05:46 +0000, Ilya Lesokhin wrote: > I don't follow. > Why can't splice use MSG_MORE for the individual pages? > Why does tcp_sendpage need to know if the MORE indicator is coming from the > user or from splice? > > I also don't understand your comment about partial writes. > Make sure that sendpage() wont end up with a stall on TCP, if the socket has not enough room to store the 16 pages provided by splice() or sendpage() Just use MSG_SENDPAGE_NOTLAST and be happy. > Thanks, > Ilya > > > -----Original Message----- > > From: Eric Dumazet [mailto:eric.duma...@gmail.com] > > Sent: Thursday, May 4, 2017 9:33 PM > > To: Ilya Lesokhin <il...@mellanox.com> > > Cc: netdev@vger.kernel.org; tls-fpga-sw-dev <tls-fpga-sw- > > d...@mellanox.com>; Dave Watson <davejwat...@fb.com> > > Subject: Re: Why do we need MSG_SENDPAGE_NOTLAST? > > > > On Thu, 2017-05-04 at 17:03 +0000, Ilya Lesokhin wrote: > > > I don't understand the need for MSG_SENDPAGE_NOTLAST and I'm hoping > > > someone can enlighten me. > > > > > > According to commit 35f9c09 ('tcp: tcp_sendpages() should call > > > tcp_push() once'): > > > "We need to call tcp_flush() at the end of the last page processed in > > > tcp_sendpages(), or else transmits can be deferred and future sends > > > stall." > > > > > > I don't understand why we need to differentiate between the user > > > setting MSG_MORE > > > and splice indicating that more data is going to be sent. > > > if the user passed MSG_MORE and didn't push any extra data, isn't it > > > the users fault? > > > Do we need it because poorly written applications were broken when > > > MSG_MORE was added to tcp_sendpage? Or is there a deeper reason? > > > > > > > The answer lies to how splice() is working. > > > > User can issue one splice without MSG_MORE semantic, right ? > > > > Still, we want an implicit MORE behavior for all individual pages, but > > the last one. > > > > > > > The reason I'm asking is that we are working on a kernel TLS > > > implementation > > > and I would like to know if we can coalesce multiple tls_sendpage > > > calls with MSG_MORE into a single > > > tls record or whether we must push out the record as soon as > > > MSG_SENDPAGE_NOTLAST is cleared? > > > > Make sure you handle partial writes (you want to coalesce 10 pages, but > > stack will only take 5 of them) > > > > >
