David Arendt wrote:
4) As the data gets expired, and snapshots get deleted, this will
inevitably lead to fragmentation, which will de-linearize writes as they
have to go into whatever holes are available in the data. How does this
affect nilfs write performance?
For now, my understanding, nilfs garbage collector moves the live (in use)
blocks to the end of logs, so holes are not created (it is correct?).
However, it leads another issue that garbage collector process, which is
nilfs_cleanerd, will consume the I/O. This is major I/O performance
bottle neck current implementation.
Since this moves files, it sounds like this could be a major issue for
flash media since it unnecessarily creates additional writes. Can this
be suppressed?
You can simply kill the nilfs_clearnerd after you mount the nilfs partition.
If you use the latest nilfs_utils, killing nilfs_cleanerd is no longer
necessary. You can use mount -o nogc. This will not start
nilfs_cleanerd. Another possibility is to let nilfs_cleanerd start and
tweak min_free_segments and max_free_segments so that cleanerd will only
do cleaning if necessary.
What about making the gc run only if the disk has been idle for, say,
20ms, unless min_free_segments is reached?
Gordan
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