Re: [RFC] Defragmentation interface

[Dave Kleikamp <shaggy@austin.ibm.com>]

On Fri, 2006-11-03 at 09:59 +1100, David Chinner wrote:

> Let me get this straight - the interface you propose for
> moving data about is:
> 
> 	read and process extents into an internal structure
> 	find range where you want to relocate
> 	find free space you want to relocate into
> 	write desired block to alloc_goal
> 	seek to allocation offset in data/alloc
> 	write length into data/alloc
> 	allocate new inode
> 	write new inode number into data/reloc to relocate blocks
> 
> What I proposed:
> 
> 	fcntl(src, FIBMAP);
> 	/* find range to relocate */
> 	open(tmp, O_CREATE);
> 	funlink(tmp);
> 	fs_get_free_list(src, policy, list);
> 	/* select free extent to use */
> 	fs_allocate_space(tmp, list[X], off, len);
> 	fs_move_data(src, tmp, off, len);
> 	close(tmp);
> 	close(src);
> 
> So the process is pretty close to the same except the interface I
> proposed does not change the location of the inode holding the data.
> The major difference is that one implementation requires 3 new
> generically useful syscalls, and the other requires every filesystem
> to implement a metadata filesystem and require root priviledges
> to use.

I agree with Dave here.  The metadata filesystem will require a lot of
overhead (and a lot of code) both in the kernel and in user-space.  The
only benefit I see, is that it can be easily extended.  This may be
useful for debugging and prototyping, but I don't like it as a solution
for adding a permanent interface.

Shaggy
-- 
David Kleikamp
IBM Linux Technology Center