enhance `MEMORY DEFRAGMENT` command

[romange]

Currently MEMORY DEFRAGMENT kicks off the asynchronous defragmentation process and replies OK

INFO STATS are not enough to understand why defragment did not do anything and the fragmentation ratio stayed high.

The goal of this issue:

1. Add more introspection by either adding summary to loads at the end of defragment run or specifically for the command - to wait for defragment process to finish and reply with the report.
2. Provide optional arguments for DEFRAGMENT so we could pass differrent parameters to be able to tune its behavior in prod
3. Add the HELP description to the command.

[kostasrim]

+1 for the stats. My only question here is why would we want to run MEMORT DEFRAGMENT manually since it runs in a background fiber anyway on fixed intervals ? In other words, what would MEMORY DEFRAGMENT do differently than the background fiber ?

[kostasrim]

Uh I now understand.

1. We run it only when the proactor is idle -- so it's not really a background task
2. We rely on CheckRequired to allow it to proceed

makes sense now. Ignore me.

[romange]

background task has a trigger condition that again needs to be improved. it also has predefined parameters of how to run defragment. MEMORY DEFRAGMENT is always triggered and may have parameters override. The goal is to understand what's wrong with the automatic system and improve it but always have the manual override as a backup.

[romange]

opened #5398

[abhijat]

@romange for the first point I have a couple of questions:

Add more introspection by either adding summary to loads at the end of defragment run or specifically for the command - to wait for defragment process to finish and reply with the report.

1. What kind of summary/statistics should be added? e.g. I can think of:

• how many objects were reallocated, object type/size
• how many objects were contained in pages below the threshold ratio so skipped from reallocation
• anything else?

2. The memory defragment command is to be changed to now block for defrag process to finish, so the stats can be reported as output, but for the background task which runs unattended, should the report be logged to dragonfly logs? Or added to info stats output etc, to show defrag stats for the last run?

[romange]

The background task does not have to report anything to logs, the focus is only on the CLI command