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

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Date:	Wed, 19 May 2010 08:32:15 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Miklos Szeredi <miklos@...redi.hu>
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, Miklos Szeredi wrote:
> 
> 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.

It should be fixed by saying "you can't always just move the page".

Copying is not evil. Complexity  to avoid copies is evil.

		Linus
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