From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail191.messagelabs.com (mail191.messagelabs.com [216.82.242.19]) by kanga.kvack.org (Postfix) with ESMTP id 3529B6008F0 for ; Wed, 19 May 2010 11:33:28 -0400 (EDT) Date: Wed, 19 May 2010 08:30:10 -0700 (PDT) From: Linus Torvalds Subject: Re: Unexpected splice "always copy" behavior observed In-Reply-To: <20100519151726.GB2516@laptop> Message-ID: References: <20100518153440.GB7748@Krystal> <1274197993.26328.755.camel@gandalf.stny.rr.com> <1274199039.26328.758.camel@gandalf.stny.rr.com> <20100519063116.GR2516@laptop> <20100519151726.GB2516@laptop> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org To: Nick Piggin Cc: Steven Rostedt , Mathieu Desnoyers , Peter Zijlstra , Frederic Weisbecker , Pierre Tardy , Ingo Molnar , Arnaldo Carvalho de Melo , Tom Zanussi , Paul Mackerras , linux-kernel@vger.kernel.org, arjan@infradead.org, ziga.mahkovec@gmail.com, davem , linux-mm@kvack.org, Andrew Morton , KOSAKI Motohiro , Christoph Lameter , Tejun Heo , Jens Axboe List-ID: On Thu, 20 May 2010, Nick Piggin wrote: > > Well I mean a full invalidate -- invalidate_mapping_pages -- so there is > literally no pagecache there at all. Umm. That won't work. Think mapped pages. You can't handle them atomically, so somebody will page-fault them in. So you'd have to have a "invalidate_and_replace()" to do it atomically while holding the mapping spinlock or something. And WHAT IS THE POINT? That will be about a million times slower than just doing the effing copy in the first place! Memory copies are _not_ slow. Not compared to taking locks and doing TLB invalidates. Linus -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org