On Fri, Jan 12, 2007 at 03:04:57PM +0100, Philippe Berthault wrote:
> Daniel Veillard a écrit :
> > I think Xen just returns -1 when the field is uninitialized, probably
> >meaning 'all physical memory'. Once you use "xm mem-max 0 ..." then it
> >consider the Dom0 domain constrained, but not before. And since there
> >are machine where it's possible to hot plug new memory this is a way to
> >not poll the current physical memory, a bit weird but that can be
> >understood.
> >
> The signed value -1, "casted" in C/C++ in unsigned integer, gives the
> value 4294967295. The Max memory value returned by virsh is 4294967292.
> There is a small difference (3), so the value returned by Xen can't be -1.
You're forgetting though, that xen measures this in terms of pages. Libvirt
converts that to bytes. The virsh converts it to KB when printing it.
$cat > demo.c <<EOF
#include <stdio.h>
int main() {
unsigned int max_pages = ~0U;
unsigned long long mem = (unsigned long long)max_pages * 4096ull;
unsigned long memkb = mem / 1024;
printf("%u %llu %lu\n",
max_pages,
mem,
memkb);
}
EOF
$ gcc -o demo demo.c
$ ./demo
4294967295 17592186040320 4294967292
Regards,
Dan.
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