linux-kernel - Re: introduce dm-snap-mv

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Message-ID: <AANLkTim9KFuP1_mrUUsMOEspxkfA=SZW2dmTX4WJbfep@mail.gmail.com>
Date:	Fri, 8 Oct 2010 17:14:27 +0800
From:	McPacino <mcpacino@...il.com>
To:	Christoph Hellwig <hch@....de>
Cc:	Daniel Phillips <phillips@...nq.net>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	dm-devel@...hat.com, Andrew Morton <akpm@...ux-foundation.org>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Nick Piggin <npiggin@...nel.dk>
Subject: Re: introduce dm-snap-mv

Hi Christoph,

I have to take care the cache problem If using the bio directly.
BHs can be released by kernel when necessary.

Is there any existing code using bio to read/write metadata
blocks? How do they handle the timing freeing bios? I really
wish to learn something form it.

Regards.

Cong Meng.



On Fri, Oct 8, 2010 at 4:22 PM, Christoph Hellwig <hch@....de> wrote:
> On Thu, Oct 07, 2010 at 02:31:14PM -0700, Daniel Phillips wrote:
>> Hi Meng,
>>
>> The patch looks sensible, however the question is: why do you want to
>> do this?  Would it not be better to generalize your metadata format to
>> accomodate the device's native blocksize?
>
> Even if it uses fixed 4k sectors it should just read them in smaller
> chunks OR even better stop using buffer heads and just read them
> manually using submit_bio.  BHs really shouldn't be used outside of
> filesystems, and even there they slowly are on their way out.
>
>
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