Feature request - Allow one to change mbuffer chunk size.

[P-EB]

Hey,

The default chunk size of 128k for mbuffer is not always ideal. Would it be possible to either make it changeable or to accept a PR with the code modifications?

Cheers! PEB

[P-EB]

Ok I made a PR that seems to do the job and also refines the way mbuffer pipes are added.

[psy0rz]

why isnt it always ideal? did you do some tests to different buffer sizes and can i see the results?

[P-EB]

I have to redo my graphs just to be sure because someone messed with the server today during my test session and I want no external tampering. Just to give context, I did a lot of poking with zfs send/receive and mbuffer manually and I counter-intuitively found 2k to be the best chunk-size in my case.

In my case the sending and receiving points are separated by about 500 kms, and multiple network layers I can't change.

I'll repaste fresh graphs tomorrow, after having make sure no one logs in and messes with my servers during the tests.

[psy0rz]

ah cool. i think i just randomly decided it should be 128k , because record size is also 128k or something.

maybe i should omit a default, since then mbuffer will automatically decide it according to page size, which is 4k usually? maybe you can try that as well?

[P-EB]

4k was less good than 2k in my case. I think your 128k rationale is a good one in general. The flexibility of the argument just seems worthwile for some specific cases.

I'm rerunning my tests I'll try to get you some graphs asap

[P-EB]

@psy0rz So, here they are.

Now that I've tweaked my zfs on the receiving side, the perf delta is quite smaller actually (only 8.5%, before it was more like 25 to 30%).

2k

128k

It's of course reproducible.

[psy0rz]

ah nice, thanks for the info!