nilfs checkpoints tied to synchronous writes

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Hello,

I have a configuration where I use qemu/qcow loop filesystems
on top a nilfs filesystem to yield writeable snapshots.

The symptom I see is the nilfs filesystem "ballooning" in size when
writing large chunks of data to the qcow loop filesystem.  I also see
_many_ nilfs checkpoints with small "NBLKINC" counts (>20  <50).

My working theory is nilfs creates checkpoints for each synchronous
write, and qcow insists on writing synchronously, thus the ballooning
of checkpoints.

One question is would it be possible to have nilfs not checkpoint so
often.  I've tried the 'nilfs-tune -i ..' to no avail - apparently
synchronous writes overrule this setting.

Thanks in advance,
Mark T.


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