From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail137.messagelabs.com (mail137.messagelabs.com [216.82.249.19]) by kanga.kvack.org (Postfix) with ESMTP id C8126600385 for ; Wed, 19 May 2010 11:29:36 -0400 (EDT) In-reply-to: (message from Linus Torvalds on Wed, 19 May 2010 07:39:11 -0700 (PDT)) Subject: Re: Unexpected splice "always copy" behavior observed References: <20100518153440.GB7748@Krystal> <1274197993.26328.755.camel@gandalf.stny.rr.com> <1274199039.26328.758.camel@gandalf.stny.rr.com> <20100519063116.GR2516@laptop> Message-Id: From: Miklos Szeredi Date: Wed, 19 May 2010 17:28:38 +0200 Sender: owner-linux-mm@kvack.org To: Linus Torvalds Cc: npiggin@suse.de, rostedt@goodmis.org, 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 List-ID: On Wed, 19 May 2010, Linus Torvalds wrote: > 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. Another limitation I found while splicing from one file to another is that stealing from the source file's page cache does not always succeed. This turned out to be because of a reference from the lru cache for freshly read pages. I'm not sure how this could be fixed. Miklos -- 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