The NOVA filesystem [LWN.net]

The NOVA filesystem

Posted Aug 6, 2017 7:50 UTC (Sun) by swanson (guest, #116493)
In reply to: The NOVA filesystem by pr1268
Parent article: The NOVA filesystem

We don't need anything so complicated as a separate utility.

The origin of the CPU-count dependence is that NOVA divides PMEM into per-CPU allocation regions. We use the current CPU ID as a hint about which region to use and avoid contention on the locks that protect it.

So moving from a smaller number of CPUs to a larger number of CPUs just means more contention for the locks. Moving from a larger number to a smaller number is no problem at all. So, our current plan is to set the CPU count very high (like 256) when the file system is created.

-steve

Number of CPUs

Posted Aug 7, 2017 7:49 UTC (Mon) by skitching (guest, #36856) [Link]

That sounds to me like "bucketing" as used in NoSQL databases or "consistent hashing" algorithms.

The NOVA filesystem

Posted Aug 7, 2017 8:50 UTC (Mon) by alonz (subscriber, #815) [Link] (1 responses)

Does this mean some memory cannot be allocated unless you have all 256 CPUs?

The NOVA filesystem

Posted Aug 7, 2017 9:20 UTC (Mon) by Cyberax (✭ supporter ✭, #52523) [Link]

I would imagine that each CPU will have several partitions assigned to it. If the number of CPUs is less than the number of partitions then some CPUs will have multiple partitions, if the reverse is true then some partitions will be shared across several CPUs.