Ceph: Designing and Implementing Scalable Storage Systems

Virtual memory settings

These are perhaps the most controversial of the settings we list in this chapter: ones that affect the kernel's management of virtual memory. Research the latter five on the net before setting; your kernel and situation may have dynamics that favor different or default settings.

vm.min_free_kbytes sizes a pool of free memory that the kernel tries to maintain in order to service allocation requests. By raising the value, we can speed up memory allocation and avoid fragmentation that confounds larger request sizes.

At the very least, though, we recommend setting vm.min_free_kbytes to 1048576, or even 2097152 unless your systems are provisioned with limited memory, in which case you should really consider getting more. ...