The maxMem field of the virDomainInfo structure is given in bytes instead of Kbytes when the domain is 0 (Domain-0). With others domains, the value of maxMem is correct. Exemple with virsh: On a system with 4 GB memory, virsh reports: # virsh dominfo 0 ... Max memory: 4294967292 kB With the same libvirt version 0.1.9 but with an older Xen (not 3.0.3), the maxMem value of Domain-0 is correct.

Daniel P. Berrange a écrit : >On Fri, Jan 12, 2007 at 11:47:16AM +0100, Philippe Berthault wrote: > >>The maxMem field of the virDomainInfo structure is given in bytes >>instead of Kbytes when the domain is 0 (Domain-0). With others domains, >>the value of maxMem is correct. >> >>Exemple with virsh: >> On a system with 4 GB memory, virsh reports: >> # virsh dominfo 0 >> ... >> Max memory: 4294967292 kB >> >>With the same libvirt version 0.1.9 but with an older Xen (not 3.0.3), >>the maxMem value of Domain-0 is correct. >> > >This sounds like a bug in Xen, rather than a bug in libvirt - we don't >have any special handling for Domain-0 - we're just passing back through >whatever data we get from Xen. > >Dan. > This problem seems to be caused by a missing initialization (in Xen or libvirt ? to be determined) because after setting the system memory size by using the "xm mem-max" command on Domain-0, the Max memory value returned by virsh is correct and reflect the value passed to the xm command. This problem of incoherent maxMem value on Domain-0 has been detected after a system reboot.

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.

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