linux-kernel - Re: Unexpected splice "always copy" behavior observed

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Message-ID: <20100518160051.GK2516@laptop>
Date:	Wed, 19 May 2010 02:00:51 +1000
From:	Nick Piggin <npiggin@...e.de>
To:	Christoph Lameter <cl@...ux.com>
Cc:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Pierre Tardy <tardyp@...il.com>, Ingo Molnar <mingo@...e.hu>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Tom Zanussi <tzanussi@...il.com>,
	Paul Mackerras <paulus@...ba.org>,
	linux-kernel@...r.kernel.org, arjan@...radead.org,
	ziga.mahkovec@...il.com, davem <davem@...emloft.net>,
	linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Tejun Heo <tj@...nel.org>, Jens Axboe <jens.axboe@...cle.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: Unexpected splice "always copy" behavior observed

On Tue, May 18, 2010 at 10:56:24AM -0500, Christoph Lameter wrote:
> On Wed, 19 May 2010, Nick Piggin wrote:
> 
> > What would be needed is to have filesystem maintainers go through and
> > enable it on a case by case basis. It's trivial for tmpfs/ramfs type
> > filesystems and I have a patch for those, but I never posted it on.yet.
> > Even basic buffer head filesystems IIRC get a little more complex --
> > but we may get some milage just out of invalidating the existing
> > pagecache rather than getting fancy and trying to move buffers over
> > to the new page.
> 
> There is a "migration" address space operation for moving pages. Page
> migration requires that in order to be able to move dirty pages. Can
> splice use that?

Hmm yes I didn't think of that, it probably could.

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