linux-kernel - Re: [Bcache v13 00/16]

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Date:	Thu, 10 May 2012 11:34:34 -0700
From:	Dan Williams <dan.j.williams@...el.com>
To:	Kent Overstreet <koverstreet@...gle.com>
Cc:	linux-bcache@...r.kernel.org, linux-kernel@...r.kernel.org,
	dm-devel@...hat.com, tejun@...gle.com,
	Alasdair G Kergon <agk@...hat.com>,
	linux-raid <linux-raid@...r.kernel.org>
Subject: Re: [Bcache v13 00/16]

On Wed, May 9, 2012 at 8:07 PM, Kent Overstreet <koverstreet@...gle.com> wrote:
> bcache: a cache for arbitrary block devices using an SSD.
>
> Short overview:
> Bcache does both writethrough and writeback caching. It presents itself as a
> new block device, a bit like say md. You can cache an arbitrary number of
> block devices with a single cache device, and attach and detach things at
> runtime - it's quite flexible.
>
> It's very fast. It uses a b+ tree for the index, along with a journal to
> coalesce index updates, and a bunch of other cool tricks like auxiliary binary
> search trees with software floating point keys for searching within btree
> nodes.
>
> Bcache is solid, production ready code. There are still bugs being found that
> affect specific configurations, but there haven't been any major issues found
> in awhile - it's well past time I started working on getting it into mainline.
>
> It's a lot of code - I tried to split it out so that it'd make some sort of
> sense for reviewing. Let me know if there's anything else I can do to make
> review easier.
>
> TODO/known issues:
>
> __up_write() needs to be exported for bcache to compile as a module - it's
> used for bypassing lockdep when traversing the btree during garbage
> collection. If someone else knows a better solution, please let me know.
>
> The userspace interface is going to change before it goes in. The general
> consensus at LSF was that we don't want yet another interface for
> probing/managing block devices, and dm exists so we may as well use that. I
> don't think anyone's started on that yet, though.

Might as well mention I've started work on a md conversion.  Nearing
the point of having RFC patches ready to post.

I'm doing it in such a way that it does not preclude a dm target from
coming along as well.  Like I mentioned to Alasdair at LSF, there's no
reason this could not be treated the same as the shared raid
personalities between dm and md.

--
Dan
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