From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753384Ab0ESPpt (ORCPT ); Wed, 19 May 2010 11:45:49 -0400 Received: from hrndva-omtalb.mail.rr.com ([71.74.56.125]:51432 "EHLO hrndva-omtalb.mail.rr.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751565Ab0ESPpr (ORCPT ); Wed, 19 May 2010 11:45:47 -0400 X-Authority-Analysis: v=1.1 cv=DB4JU8ZWelvwd5d0x20oybKyR86uyiSly0XbcMdosrc= c=1 sm=0 a=8EtQVlZUVNwA:10 a=hO-oPbc3tlwA:10 a=7U3hwN5JcxgA:10 a=Q9fys5e9bTEA:10 a=gMqfjgEr1zLu/65IO0LwxA==:17 a=n60Vwz4mJqZaziYBhsAA:9 a=-5B0SYW93aXBYXS8RHWtPZ6HBYIA:4 a=PUjeQqilurYA:10 a=gMqfjgEr1zLu/65IO0LwxA==:117 X-Cloudmark-Score: 0 X-Originating-IP: 74.67.89.75 Subject: Re: Unexpected splice "always copy" behavior observed From: Steven Rostedt Reply-To: rostedt@goodmis.org To: Miklos Szeredi Cc: Linus Torvalds , npiggin@suse.de, mathieu.desnoyers@efficios.com, peterz@infradead.org, fweisbec@gmail.com, tardyp@gmail.com, mingo@elte.hu, acme@redhat.com, tzanussi@gmail.com, paulus@samba.org, linux-kernel@vger.kernel.org, arjan@infradead.org, ziga.mahkovec@gmail.com, davem@davemloft.net, linux-mm@kvack.org, akpm@linux-foundation.org, kosaki.motohiro@jp.fujitsu.com, cl@linux-foundation.org, tj@kernel.org, jens.axboe@oracle.com In-Reply-To: References: <20100518153440.GB7748@Krystal> <1274197993.26328.755.camel@gandalf.stny.rr.com> <1274199039.26328.758.camel@gandalf.stny.rr.com> <20100519063116.GR2516@laptop> <1274280968.26328.774.camel@gandalf.stny.rr.com> Content-Type: text/plain; charset="ISO-8859-15" Organization: Kihon Technologies Inc. Date: Wed, 19 May 2010 11:45:42 -0400 Message-ID: <1274283942.26328.783.camel@gandalf.stny.rr.com> Mime-Version: 1.0 X-Mailer: Evolution 2.28.3 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 2010-05-19 at 17:33 +0200, Miklos Szeredi wrote: > On Wed, 19 May 2010, Linus Torvalds wrote: > > Btw, since you apparently have a real case - is the "splice to file" > > always just an append? IOW, if I'm not right in assuming that the only > > sane thing people would reasonable care about is "append to a file", then > > holler now. > > Virtual machines might reasonably need this for splicing to a disk > image. This comes down to balancing speed and complexity. Perhaps a copy is fine in this case. I'm concerned about high speed tracing, where we are always just taking pages from the trace ring buffer and appending them to a file or sending them off to the network. The slower this is, the more likely you will lose events. If the "move only on append to file" is easy to implement, I would really like to see that happen. The speed of splicing a disk image for a virtual machine only impacts the patience of the user. The speed of splicing tracing output, impacts how much you can trace without losing events. -- Steve