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

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Date:	Wed, 19 May 2010 17:28:38 +0200
From:	Miklos Szeredi <miklos@...redi.hu>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
CC:	npiggin@...e.de, rostedt@...dmis.org,
	mathieu.desnoyers@...icios.com, peterz@...radead.org,
	fweisbec@...il.com, tardyp@...il.com, mingo@...e.hu,
	acme@...hat.com, tzanussi@...il.com, paulus@...ba.org,
	linux-kernel@...r.kernel.org, arjan@...radead.org,
	ziga.mahkovec@...il.com, davem@...emloft.net, linux-mm@...ck.org,
	akpm@...ux-foundation.org, kosaki.motohiro@...fujitsu.com,
	cl@...ux-foundation.org, tj@...nel.org, jens.axboe@...cle.com
Subject: Re: Unexpected splice "always copy" behavior observed

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
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