On Wed, Feb 26, 2020 at 04:33:13PM +0100, Michal Prívozník wrote: > 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@xxxxxxxxxx> > > --- > > 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. I'm glad to see this suggestion because I was tempted to round it up to 64M as well, so works for me. Pavel
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