linux-kernel - Re: [dm-devel] [RFC][PATCH] dm-cache: block level disk cache target for device mapper

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Date:	Fri, 1 Dec 2006 02:16:15 -0500
From:	"Ming Zhao" <mingzhao99th@...il.com>
To:	"device-mapper development" <dm-devel@...hat.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [dm-devel] [RFC][PATCH] dm-cache: block level disk cache target for device mapper

On 11/30/06, Jens Wilke <jens.wilke@...ibm.com> wrote:
> - You don't keep track of I/O on the fly to the cache that is mapped
> directly in cache_hit(). How do you make sure that this I/O is completed
> before you replace a cache block?

The previous I/O from cache hit and the later I/O for cache
replacement should be queued in order on the cache block device - is
this a safe assumption?

> - The cache block index is hashed, this means the cache data blocks are not
> clustered. I don't think you can solve this problem with a proper hash function.
> Perhaps you should consider a (B-)Tree structure for that.

The current hash algorithm does clustering to some extent by mapping
consecutive blocks from the source device to consecutive blocks on the
cache device. But I agree that more sophisticated algorithms can be
studied.

Thanks a lot for the suggestions. I will try to incorporate them in
the next patch.

- Ming
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