Message-ID: <47C40269.7060309@emc.com>
Date: Tue, 26 Feb 2008 07:13:29 -0500
From: Ric Wheeler <ric@emc.com>
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To: Jeff Garzik <jeff@garzik.org>
CC: Jamie Lokier <jamie@shareable.org>, linux-kernel@vger.kernel.org,
       linux-fsdevel@vger.kernel.org, Chris Wedgwood <cw@f00f.org>
Subject: Re: Proposal for "proper" durable fsync() and fdatasync()
References: <20080226072649.GB30238@shareable.org> <47C3C33F.1070908@garzik.org>
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Jeff Garzik wrote:
> Jamie Lokier wrote:
>> By durable, I mean that fsync() should actually commit writes to
>> physical stable storage,
> 
> Yes, it should.
> 
> 
>> I was surprised that fsync() doesn't do this already.  There was a lot
>> of effort put into block I/O write barriers during 2.5, so that
>> journalling filesystems can force correct write ordering, using disk
>> flush cache commands.
>>
>> After all that effort, I was very surprised to notice that Linux 2.6.x
>> doesn't use that capability to ensure fsync() flushes the disk cache
>> onto stable storage.
> 
> It's surprising you are surprised, given that this [lame] fsync behavior 
> has remaining consistently lame throughout Linux's history.

Maybe I am confused, but isn't this is what fsync() does today whenever 
barriers are enabled (the fsync() invalidates the drive's write cache).

ric
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