Proper size of NOVA not reflected when mounting on a partition

[ahuja-gautam]

Hi,
I was trying to mount NOVA on small PMEM devices (preferably less than 64MiB).
For that, I emulated a permanent memory device using memmap and created 2 partitions. While trying to mount NOVA on the partition, the file system size shows 135Mib.
Is there a reason why this happens? I was expecting the size to be ~64Mib

Step 1: Created partition on emulated PMEM

Step 2: Mounting NOVA and viewing size

[Andiry]

I will take a look.

[ahuja-gautam]

Thank you Andiry. Could you also let me know what the minimum supported device size is for Nova?

[Andiry]

I cannot reproduce the issue.

I tried with a 64MB pmem: memmap=64M!31G
Mount with NOVA:

mount -t NOVA -o init /dev/pmem1 /mnt/ramdisk/
df -H

Result:

/dev/pmem1       68M   43M   25M  64% /mnt/ramdisk

dmesg:

[  244.299035] nova: creating an empty nova of size 67108864
[  244.301023] nova: NOVA initialization finish
[  244.301029] nova: Current epoch id: 0
[  246.668166] nova: nova_stats: total 4k free blocks 0x178d

Here I enable the logging in nova_statfs. Here it consumes 43MB for reserved space and only has ~6K free 4K pages, which is roughly 24MB.

To answer your second question, I have no idea, but NOVA has reserved 1/6 space for protection reasons, and fixed space (start from the head) for various metadata and states. I think the minimal support size is 64MB.

[ahuja-gautam]

Hi, can you verify this for a partition as well? I was facing this issue for a 64MB partition on a 128MB pmem