Re: [PATCH] remove useless highmem bounce from loop/cryptoloop

[Ben Slusky <sluskyb@paranoiacs.org>]

On Thu, 30 Oct 2003 13:30:00 -0800, Andrew Morton wrote:
> Ben, I confess that I'd forgotten about #1198.  I'll take a look at your
> memory allocation fix - it seems to be unfortunately large, but we may need
> to go that way.

The current memory allocation procedure really is inadequate. It worked
ok up thru 2.4 because the loop device was used almost exclusively
as a nifty hack to make an initrd or to double-check the ISO you just
created. Throw strong crypto into the mix and it becomes reasonable to
have your laptop mount all its filesystems and swap off of loop devices.

> One question is: why do we go down a different code path for blockdevs
> nowadays anyway?  The handoff to the loop thread seems to work OK for
> file-backed loop, and providing a bmap() for blockdevs is easy enough?

The code path for file-backed loop handles one page at a time, as that's
the limit of the FS interface. Block-backed loop devices can throw
huge bios at their backing device with one make_request. If we could
get both working on the same code path, would that be worth hobbling
block-backed loop?

-- 
Ben Slusky                      | If you're not part of the
sluskyb@paranoiacs.org          | solution, there's good money
sluskyb@stwing.org              | to be made in prolonging the
PGP keyID ADA44B3B              | problem.      www.despair.com