Re: Memory locking limit and zero-copy migrations

On Fri, Aug 19, 2022 at 4:08 AM Milan Zamazal <mzamazal(a)redhat.com&gt; wrote: > > Not sure whether you already know this, but I had a hard time > > differentiating the two concepts: > > 1. memlock hard limit(shown by prlimit): the hard limit for locked host > > memory > > 2. memtune hard limit(memtune->hard_limit): the hard limit for in-use > host > > memory, this memory can be swapped out. > > No, I didn't know it, thank you for pointing this out. Indeed, 2. is > what both the libvirt and kernel documentation seem to say, although not > so clearly. > > But when I add <memtune> with <hard_limit> to the domain XML and then > start the VM, I can see the limit shown by `prlimit -l' is increased > accordingly. This is good for my use case, but does it match what you > say about the two concepts? memtune->hard_limit(hard limit of in-use memory) actually takes effect via cgroup, you can check the value by: # virsh memtune uefi1 hard_limit : 134217728 soft_limit : unlimited swap_hard_limit: unlimited # cat /sys/fs/cgroup/memory/machine.slice/machine-qemu\\x2d6\\x2duefi1.scope/libvirt/memory.limit_in_bytes 137438953472 When vm starts with memtune->hard_limit set in domain XML, memlock hard limit( hard_limit of locked memory, shown by 'prlimit -l')will be set to the value of memtune->hard_limit. This's probably because memlock hard limit must be less than memtune->hard_limit.