On Mon, Feb 1, 2010 at 4:08 AM, Artur Grabowski <a...@blahonga.org> wrote:
> caller holds lock on kernel_map. getpage pool is empty, caller wakes
> up the getpage thread, goes to sleep (still holding the kernel_map
> lock), getpage thread wakes up, deadlocks on the kernel_map lock. It's
> not an easily detectable recursion either, so we don't panic when it
> happens, we just hang.
>
> amd64 can avoid it thanks to the direct map (no kernel_map involed when
> calling getpage).
>
> We could try some magic with allocating from a pool with NOWAIT and
> then fall back to kmem_map when that fails, but the logic would become
> hairy. Maybe a pool allocator with those semantics?
We could keep a couple entries always available. Then the logic goes like this:
if (alloc(NOWAIT))
use freelist;
else
while (freelist < minsize)
alloc(NOWAIT).
