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Re: NOW: o_direct -- WAS: Re: WARNING in xfs_lwr.c, xfs_write()

To: xfs@xxxxxxxxxxx
Subject: Re: NOW: o_direct -- WAS: Re: WARNING in xfs_lwr.c, xfs_write()
From: Stan Hoeppner <stan@xxxxxxxxxxxxxxxxx>
Date: Thu, 27 May 2010 19:25:56 -0500
In-reply-to: <20100527114736.GA13112@xxxxxxxxxxxxx>
References: <20100523002023.41f5a5c8@xxxxxxxxxxxxxxxxxxxxxxx> <20100523101856.GL2150@dastard> <20100523092344.0fcaab42@xxxxxxxxxxxxxxxxxxxxxxx> <4BF9FCA8.8090906@xxxxxxxxxxxxxxxxx> <20100524143428.6f3a117c@xxxxxxxxxxxxxxxxxxxxxxxxxxxxx> <20100526070620.GT2150@dastard> <4BFD3926.6040208@xxxxxxxxxxxxxxxxx> <20100527114736.GA13112@xxxxxxxxxxxxx>
User-agent: Mozilla/5.0 (Windows; U; Windows NT 5.0; en-US; rv:1.9.1.9) Gecko/20100317 Thunderbird/3.0.4
Christoph Hellwig put forth on 5/27/2010 6:47 AM:
> O_DIRECT is not a Posix standard and not very portable.  It originated
> on IRIX, and Linux inherited it during the 2.4 kernel series days.
> These days FreeBSD/NetBSD and AIX support it as well, but for example
> Solaris, HP-UX and OpenBSD don't, nevermind Windows or Mac OS.
> 
> I have no idea why the MTAs don't want to use it - it's generally easier
> to use then memory mapped I/O, and has much more deterministic
> performance.

Thanks for the background Christoph.  I can now see why Postfix and Dovecot in
particular don't use O_DIRECT: portability.  They both are developed to run on
every Unix/like OS you mention above, half of which don't offer O_DIRECT.  I'm
guessing the same may likely be true for the other SMTP MTAs and IMAP servers.

-- 
Stan

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