linux-kernel - Re: O_DIRECT question

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Message-ID: <Pine.LNX.4.64.0701101902270.3594@woody.osdl.org>
Date:	Wed, 10 Jan 2007 19:05:30 -0800 (PST)
From:	Linus Torvalds <torvalds@...l.org>
To:	Aubrey <aubreylee@...il.com>
cc:	Hua Zhong <hzhong@...il.com>, Hugh Dickins <hugh@...itas.com>,
	linux-kernel@...r.kernel.org, hch@...radead.org,
	kenneth.w.chen@...el.com, akpm@...l.org, mjt@....msk.ru
Subject: Re: O_DIRECT question

On Thu, 11 Jan 2007, Aubrey wrote:
>
> Now, my question is, is there a existing way to mount a filesystem
> with O_DIRECT flag? so that I don't need to change anything in my
> system. If there is no option so far, What is the right way to achieve
> my purpose?

The right way to do it is to just not use O_DIRECT. 

The whole notion of "direct IO" is totally braindamaged. Just say no.

	This is your brain: O
	This is your brain on O_DIRECT: .

	Any questions?

I should have fought back harder. There really is no valid reason for EVER 
using O_DIRECT. You need a buffer whatever IO you do, and it might as well 
be the page cache. There are better ways to control the page cache than 
play games and think that a page cache isn't necessary.

So don't use O_DIRECT. Use things like madvise() and posix_fadvise() 
instead. 

		Linus
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