linux-kernel - Re: [ANNOUNCE] Ramback: faster than a speeding bullet

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Date:	Mon, 10 Mar 2008 22:03:52 +0100
From:	Lars Marowsky-Bree <lmb@...e.de>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Daniel Phillips <phillips@...nq.net>
Cc:	Grzegorz Kulewski <kangur@...com.net>, linux-kernel@...r.kernel.org
Subject: Re: [ANNOUNCE] Ramback: faster than a speeding bullet

On 2008-03-10T09:37:37, Alan Cox <alan@...rguk.ukuu.org.uk> wrote:

> Why - your chunks simply become a linked list in write barrier order.
> Solve your bitmap sweep cost as well. As you are already making a copy
> before going to backing store you don't have the internal consistency
> problems of further writes during the I/O.

You get duplicated blocks though. But yes, I agree - write-backs to the
disk must be ordered, other it's going to be too unreliable in practice.

An in-memory buffer for a log-structured block device.

> Yes you may need to throttle in the specific case of having too many
> copies of pages sitting in the queue - but surely that would be the set of
> pages that are written but not yet committed from a previous store
> barrier ?

You could switch from a journal like the above to a bitmap when this
overrun occurs. (Typical problem in replication.) SteelEye holds a
patent on that though, as far as I know.


Regards,
    Lars

-- 
Teamlead Kernel, SuSE Labs, Research and Development
SUSE LINUX Products GmbH, GF: Markus Rex, HRB 16746 (AG Nürnberg)
"Experience is the name everyone gives to their mistakes." -- Oscar Wilde

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