Re: [Qemu-devel] [PATCH] exec: limit system memory size

["Michael S. Tsirkin" <mst@redhat.com>]

On Mon, Nov 04, 2013 at 12:22:35PM +0100, Paolo Bonzini wrote:
> Il 04/11/2013 12:14, Michael S. Tsirkin ha scritto:
> >> > 
> >> > This patch looks good; however, on top of it can you test 
> >> > kvm-unit-tests with TARGET_PHYS_ADDR_SPACE_BITS=64 and see whether 
> >> > there is a measurable slowdown (in the inl_from_qemu tests)?  If not, 
> >> > we can just get rid of TARGET_PHYS_ADDR_SPACE_BITS in exec.c.
> > I'd rather we fixed a bug first - we need to fix it on stable too - any
> > cleanups can come on top.
> 
> This is not necessarily a cleanup.  Getting rid of
> TARGET_PHYS_ADDR_SPACE_BITS in exec.c means fixing device-to-device DMA
> bugs for example.
> 
> Of course a smaller patch can be done that avoids the renaming of L2_*
> constants.
> 
> > Also, I'm not sure what will this test tell
> > us: inl reads io space, not memory, right?
> 
> The number of levels in the dispatch radix tree is independent of the
> size of the AddressSpace; it is P_L2_LEVELS for both the 64K io space
> and the 2^TARGET_PHYS_ADDRESS_SPACE_BITS memory space.
> 
> Paolo

Hmm I think it's *at most* that deep but can be more shallow, no?

-- 
MST