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Date: Wed, 19 May 2010 07:59:48 -0700 (PDT)
From: Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: Unexpected splice "always copy" behavior observed
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To: Steven Rostedt <rostedt@goodmis.org>
Cc: Nick Piggin <npiggin@suse.de>, Mathieu Desnoyers <mathieu.desnoyers@efficios.com>, Peter Zijlstra <peterz@infradead.org>, Frederic Weisbecker <fweisbec@gmail.com>, Pierre Tardy <tardyp@gmail.com>, Ingo Molnar <mingo@elte.hu>, Arnaldo Carvalho de Melo <acme@redhat.com>, Tom Zanussi <tzanussi@gmail.com>, Paul Mackerras <paulus@samba.org>, linux-kernel@vger.kernel.org, arjan@infradead.org, ziga.mahkovec@gmail.com, davem <davem@davemloft.net>, linux-mm@kvack.org, Andrew Morton <akpm@linux-foundation.org>, KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>, Christoph Lameter <cl@linux-foundation.org>, Tejun Heo <tj@kernel.org>, Jens Axboe <jens.axboe@oracle.com>
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On Wed, 19 May 2010, Steven Rostedt wrote:

> On Wed, 2010-05-19 at 07:39 -0700, 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.
> 
> That's understandable. For the use cases of splice I use, I work to make
> it page aligned and full pages. Anyone else using splice for
> optimizations, should do the same. It only makes sense.
> 
> The end of buffer may not be a full page, but then it's the end anyway,
> and I'm not as interested in the speed.

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.

		Linus

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