Re: [libvirt PATCH] daemon: set default memlock limit for systemd service

On 2/26/20 4:07 PM, Pavel Hrdina wrote: > The default memlock limit is 64k which is not enough to start a single > VM. The requirements for one VM are 12k, 8k for eBPF map and 4k for eBPF > program, however, it fails to create eBPF map and program with 64k limit. > By testing I figured out that the minimal limit is 80k to start a single > VM with functional eBPF and if I add 12k I can start another one. > > This leads into following calculation: > > 80k as memlock limit worked to start a VM with eBPF which means there > is 68k of lock memory that I was not able to figure out what was using > it. So to get a number for 4096 VMs: > > 68 + 12 * 4096 = 49220 > > If we round it up we will get 49M of memory lock limit to support 4096 > VMs with default map size which can hold 64 entries for devices. > > This should be good enough as a sane default and users can change it if > the need to. > > Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1807090 > > Signed-off-by: Pavel Hrdina <phrdina(a)redhat.com&gt; > --- > src/remote/libvirtd.service.in | 5 +++++ > 1 file changed, 5 insertions(+) > > diff --git a/src/remote/libvirtd.service.in b/src/remote/libvirtd.service.in > index 9c8c54a2ef..8a3ace5bdb 100644 > --- a/src/remote/libvirtd.service.in > +++ b/src/remote/libvirtd.service.in > @@ -40,6 +40,11 @@ LimitNOFILE=8192 > # A conservative default of 8 tasks per guest results in a TasksMax of > # 32k to support 4096 guests. > TasksMax=32768 > +# With cgroups v2 there is no devices controller anymore, we have to use > +# eBPF to control access to devices. In order to do that we create a eBPF > +# hash MAP which locked memory. The default map size for 64 devices together s/locked/locks/ > +# with program takes 12k per guest which results in 49M to support 4096 guests. > +LimitMEMLOCK=49M Should we round this up to the nearest power of two? 49MB looks just ugly. This is just a limit, it doesn't mean that libvirtd will lock whole 49MB (or 64MB as I suggest) right from the beginning.