Subject: Re: Integration of SCST in the mainstream Linux kernel
From: James Bottomley <James.Bottomley@HansenPartnership.com>
To: Vladislav Bolkhovitin <vst@vlnb.net>
Cc: Bart Van Assche <bart.vanassche@gmail.com>,
       Linus Torvalds <torvalds@linux-foundation.org>,
       Andrew Morton <akpm@linux-foundation.org>,
       FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>,
       linux-scsi@vger.kernel.org, scst-devel@lists.sourceforge.net,
       linux-kernel@vger.kernel.org
In-Reply-To: <47A73C86.3060604@vlnb.net>
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Date: Mon, 04 Feb 2008 11:06:06 -0600
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On Mon, 2008-02-04 at 19:25 +0300, Vladislav Bolkhovitin wrote:
> James Bottomley wrote:
> >>Vladislav Bolkhovitin wrote:
> >>So, James, what is your opinion on the above? Or the overall SCSI target 
> >>project simplicity doesn't matter much for you and you think it's fine 
> >>to duplicate Linux page cache in the user space to keep the in-kernel 
> >>part of the project as small as possible?
> > 
> > 
> > The answers were pretty much contained here
> > 
> > http://marc.info/?l=linux-scsi&m=120164008302435
> > 
> > and here:
> > 
> > http://marc.info/?l=linux-scsi&m=120171067107293
> > 
> > Weren't they?
> 
> No, sorry, it doesn't look so for me. They are about performance, but 
> I'm asking about the overall project's architecture, namely about one 
> part of it: simplicity. Particularly, what do you think about 
> duplicating Linux page cache in the user space to have zero-copy cached 
> I/O? Or can you suggest another architectural solution for that problem 
> in the STGT's approach?

Isn't that an advantage of a user space solution?  It simply uses the
backing store of whatever device supplies the data.  That means it takes
advantage of the existing mechanisms for caching.

James


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