linux-kernel - Re: O_DIRECT question

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Message-Id: <200701201719.15341.vda.linux@googlemail.com>
Date:	Sat, 20 Jan 2007 17:19:15 +0100
From:	Denis Vlasenko <vda.linux@...glemail.com>
To:	Linus Torvalds <torvalds@...l.org>
Cc:	Nick Piggin <nickpiggin@...oo.com.au>,
	Aubrey <aubreylee@...il.com>, 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 Thursday 11 January 2007 16:50, Linus Torvalds wrote:
> 
> On Thu, 11 Jan 2007, Nick Piggin wrote:
> > 
> > Speaking of which, why did we obsolete raw devices? And/or why not just
> > go with a minimal O_DIRECT on block device support? Not a rhetorical
> > question -- I wasn't involved in the discussions when they happened, so
> > I would be interested.
> 
> Lots of people want to put their databases in a file. Partitions really 
> weren't nearly flexible enough. So the whole raw device or O_DIRECT just 
> to the block device thing isn't really helping any.
> 
> > O_DIRECT is still crazily racy versus pagecache operations.
> 
> Yes. O_DIRECT is really fundamentally broken. There's just no way to fix 
> it sanely. Except by teaching people not to use it, and making the normal 
> paths fast enough (and that _includes_ doing things like dropping caches 
> more aggressively, but it probably would include more work on the device 
> queue merging stuff etc etc).

What will happen if we just make open ignore O_DIRECT? ;)

And then anyone who feels sad about is advised to do it
like described here:

http://lkml.org/lkml/2002/5/11/58
--
vda
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