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To: Ryan Cumming <bodnar42@phalynx.dhs.org>
Cc: linux-kernel@vger.kernel.org
Subject: Re: Special Kernel Modification 
In-Reply-To: Your message of "Sun, 04 Nov 2001 19:13:15 PST."
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Date: Mon, 05 Nov 2001 00:52:51 -0500
From: Jeff Dike <jdike@karaya.com>
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bodnar42@phalynx.dhs.org said:
> >  Mounting it synchronous will  disable caching in the VM.  
> Who told
> you that? Synchronous mounting turns off write buffering. Even with
> "-o sync" writes will still end up in the page cache, they'll just be
> commited immediately.

Ummm, how about O_DIRECT instead of O_SYNC (or maybe as well, my googling
hasn't been clear on whether O_DIRECT bypasses the cache on writes as well)?

All IO bypasses the virtual machine cache, so there's no multiple caching.

> Er, it will be shared in the host's context, but each VM will still
> have  their own copy in the page cache. This is no better than a
> COW'ed block device 

Nope.  You O_DIRECT here as well.

				Jeff

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