From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail190.messagelabs.com (mail190.messagelabs.com [216.82.249.51]) by kanga.kvack.org (Postfix) with ESMTP id B52A76B021D for ; Wed, 19 May 2010 10:42:20 -0400 (EDT) Date: Wed, 19 May 2010 07:39:11 -0700 (PDT) From: Linus Torvalds Subject: Re: Unexpected splice "always copy" behavior observed In-Reply-To: <20100519063116.GR2516@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> 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 Wed, 19 May 2010, Nick Piggin wrote: > > We can possibly do an attempt to invalidate existing pagecache and > then try to install the new page. Yes, but that's going to be rather hairier. We need to make sure that the filesystem doesn't have some kind of dirty pointers to the old page etc. Although I guess that should always show up in the page counters, so I guess we can always handle the case of page_count() being 1 (only page cache) and the page being unlocked. So I'd much rather just handle the "append to the end". The real limitation is likely always going to be the fact that it has to be page-aligned and a full page. For a lot of splice inputs, that simply won't be the case, and you'll end up copying for alignment reasons anyway. 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