[dm-devel] [PATCHES] convert dm-thin to use dm-bufio

[Mikulas Patocka <mpatocka redhat com>]

Hi

I created patches that convert dm-thin to use dm-bufio interface (so that 
it is consistent with dm-zeroed and dm-multisnap).

The patches are here:
http://people.redhat.com/mpatocka/patches/kernel/dm-thinp-bufio/

Advantages:

* It uses kmalloc, __get_free_pages or __vmalloc, so the block size is not 
limited and memory fragmentation is not an issue. The original code only 
used kmalloc.

* It has dynamic cache sizing, cache size can be configured by the user. 
In case of inactivity over some time (a buffer is unused for a minute), 
the buffers are freed. The original code had cache size hardcoded and it 
couldn't be changed.

* Submit bios directly (if we can) without dm-io layer.

Notes:

* Buffer locking is not supported, I suppose it is not used for anything 
anyway. If it is used, tell me, I can add it after reviewing it.

* dm_bm_rebind_block_device changes the block device, but it is not used 
for anything (dm-thinp never changes the device). I think it could be 
removed.

* Two small bugs in dm-thin are fixed --- not closing the superblock 
buffer on exit and improper termination sequence (the block devices were 
closed before the buffer interface exited).

Mikulas