Re: [Qemu-devel] [PATCH] pc: madvise(MADV_DONTNEED) memory on reset

[Blue Swirl]

On 2/24/10, Anthony Liguori <address@hidden> wrote:
> If you compare the RSS of a freshly booted guest and the same guest after a
>  reboot, it's very likely the freshly booted guest will have an RSS that is
>  much lower the the rebooted guest because the previous run of the guest 
> faulted
>  in all available memory.
>
>  This patch addresses this issue by using madvise() during reset.  It only
>  resets RAM areas which means it has to be done in the machine.  I've only 
> done
>  this for the x86 target because I'm fairly confident that this is allowed
>  architecturally on x86 although I'm not sure this is universely true.
>
>  This does not appear to have an observable cost with a large memory guest and
>  I can't really think of any down sides.

I think it would be much cleaner to make the madvise() calls from
exec.c, now you are duplicating some of the functionality there. The
calls could be controlled by a global variable (set only in pc.c) so
non-PC architectures would not be disturbed.