On Wed, Jul 22, 2020 at 12:02:59PM -0700, Richard Henderson wrote: > On 7/22/20 9:44 AM, Daniel P. Berrangé wrote: > > OpenStack uses TCG in alot of their CI infrastructure for example > > and runs multiple VMs. If there's 4 VMs, that's another 4 GB of > > RAM usage just silently added on top of the explicit -m value. > > > > I wouldn't be surprised if this pushes CI into OOM, even without > > containers or cgroups being involved, as they have plenty of other > > services consuming RAM in the CI VMs. > > I would hope that CI would also supply a -tb_size to go along with that -m > value. Because we really can't guess on their behalf.
I've never even seen mention of -tb_size argument before myself, nor seen anyone else using it and libvirt doesn't set it, so I think this is not a valid assumption. > > The commit 600e17b261555c56a048781b8dd5ba3985650013 talks about this > > minimizing codegen cache flushes, but doesn't mention the real world > > performance impact of eliminating those flushes ? > > Somewhere on the mailing list was this info. It was so dreadfully slow it was > *really* noticable. Timeouts everywhere. > > > Presumably this makes the guest OS boot faster, but what's the before > > and after time ? And what's the time like for values in between the > > original 32mb and the new 1 GB ? > > But it wasn't "the original 32MB". > It was the original "ram_size / 4", until that broke due to argument parsing > ordering. Hmm, 600e17b261555c56a048781b8dd5ba3985650013 says it was 32 MB as the default in its commit message, which seems to match the code doing #define DEFAULT_CODE_GEN_BUFFER_SIZE_1 (32 * MiB) > I don't know what CI usually uses, but I usually use at least -m 4G, sometimes > more. What's the libvirt default? There's no default memory size - its up to whomever/whatever creates the VMs to choose how much RAM is given. Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|