Re: [Qemu-devel] [PATCH 03/15] coroutine-ucontext: reduce stack size to 64kB

[Paolo Bonzini]

On 28/06/2016 11:01, Peter Lieven wrote:
> evaluation with the recently introduced maximum stack size monitoring revealed
> that the actual used stack size was never above 4kB so allocating 1MB stack
> for each coroutine is a lot of wasted memory. So reduce the stack size to
> 64kB which should still give enough head room.

If we make the stack this much smaller, there is a non-zero chance of
smashing it.  You must add a guard page if you do this (actually more
than one because QEMU will happily have stack frames as big as 16 KB).
The stack counts for RSS but it's not actually allocated memory, so why
does it matter?

Paolo