Re: [Qemu-devel] [PATCH 07/15] qapi: use mmap for QmpInputVisitor

[Peter Lieven]

Am 28.06.2016 um 11:29 schrieb Dr. David Alan Gilbert:
> * Peter Lieven (address@hidden) wrote:
> > this struct is approx 75kB
> I wonder why it's so large.
>
> The stack size in QmpInputVisitor; it's got a 1024 element stack
> (QIV_STACK_SIZE) and I bet we never use anywhere near that.
>
> But even then that's 1024 * a 3 pointer stack object, 24 bytes -
> I don't see where the rest of that 75kB comes from.

Sorry, I had a wrong size in mind. Its 24736 bytes. But thats
still larger than expecetd, right?

> I'm a little wary about turning all these malloc's into mmap's
> because we do seem to use things like input visitors for small
> things; don't the cost of doing the mmap's add up in time
> instead of space?

Sure, we should discuss this. The series should act as a base for
discussion.

None of the things I changed into mmap are continously called
during VM runtime. So it most likely only happens at setup of the
vServer.

It seems that the worst impact hat the PhysPageMap in exec.c

Peter