Re: [dm-devel] introduce dm-snap-mv

[McPacino <mcpacino gmail com>]

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 lst 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.
>
>