I've been looking into the LVM snapshot/memory allocation troubles and will try to come up with a fix.

FYI: In doing more searching for information about the problem, I did come across this: http://www.redhat.com/archives/dm-devel/2004-January/msg00068.html

"The problem seems to be that dm-ioctl-v4.c sets the PF_MEMALLOC flag for the current process.

Lookaing at the memory allocator (__alloc_page) this means that the VM will think the memory allocation is already running (and this is a recursion) so it will not try to free pages / rebalance page or whatever." ...

I'm looking into sharing memory between the snapshots instead of giving each snapshot its own private allocation of pages for I/O. (As I'd like to scale to a large number of snapshots, and don't want to need >1 MB of kernel memory per snapshot.)