Re: [RFC] new free space caching stuff

[Linda Knippers <linda.knippers@hp.com>]

Chris Mason wrote:
> On Thu, May 21, 2009 at 02:43:52PM -0400, Josef Bacik wrote:
>> Hello,
>>
>> Okay I'm looking at redoing all of this stuff again, and I'd like to make this
>> the last time, so I'm going to outline what we currently have, what the problems
>> are with it, and what I want to do.  I would appreciate any/all input so I can
>> try and get this right the first time.
>>
> 
> Josef and I hashed this out someone on IRC.  I think the bitmaps alone
> aren't going to scale all that well for huge filesystems, so he is
> looking into a hybrid bitmap/extent approach based on the size of the
> free space.

I don't know if this is of any interest but I thought I'd provide a
pointer to the AdvFS design spec for space allocation.
http://advfs.svn.sourceforge.net/viewvc/advfs/advfs_design_docs_v1/porting_designs/storage_allocation.pdf?revision=1

The Tru64 version of AdvFS used bitmaps but this was changed during the
port to HP-UX to
use a combination of b-trees.  Both the original and new designs are
discussed in
section 2 of the spec and there's a description of other design options
considered but then rejected.

The docs in the original tarball I posted were not very user friendly so
I checked them into an svc tree to make them a little easier to browse.
If it will be useful, I can do the same with the source code.

-- ljk

> -chris
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