Autotune mds memory target

[batrick]

https://github.com/ceph/ceph/pull/39550/files

[bengland2]

This reminds me of this bz. You don't want to allocate a lot of memory initially to the MDS cache if you don't know that it's needed, but the small default won't work for millions of files. if you wait, then will there be enough memory to increase cache size later on? Wouldn't the linode VMs have to be resized (ballooned) for this to avoid OOM problems?

[sebastian-philipp]

https://tracker.ceph.com/issues/50883