linux-kernel - Re: O_DIRECT question

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Message-ID: <45BA3343.8070703@cfl.rr.com>
Date:	Fri, 26 Jan 2007 11:58:43 -0500
From:	Phillip Susi <psusi@....rr.com>
To:	Mark Lord <lkml@....ca>
CC:	Denis Vlasenko <vda.linux@...glemail.com>,
	Michael Tokarev <mjt@....msk.ru>,
	Linus Torvalds <torvalds@...l.org>, Viktor <vvp01@...ox.ru>,
	Aubrey <aubreylee@...il.com>, Hua Zhong <hzhong@...il.com>,
	Hugh Dickins <hugh@...itas.com>, linux-kernel@...r.kernel.org,
	hch@...r.kernel.org
Subject: Re: O_DIRECT question

Mark Lord wrote:
> You guys need to backup in this thread.
> 
> Every example of O_DIRECT here could be replaced with
> calls to mmap(), msync(), and madvise() (or posix_fadvise).
> 
> In addition to being at least as fast as O_DIRECT,
> these have the added benefit of using the page cache (avoiding reads for 
> data already present, handling multiple
> users of the same data, etc..).

Please actually _read_ the thread.  In every one of my posts I have 
shown why this is not the case.

To briefly rehash the core of the argument, there is no way to 
asynchronously manage IO with mmap, msync, madvise -- instead you take 
page faults or otherwise block, thus stalling the pipeline.

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