Ubuntu 20.10

Enabling memlock for rtpmidi on Ubuntu 20.10

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In version 0.5.2 of McLaren Labs’ rtpmidi, we made the use of locked memory the default. Locked memory dedicates fixed RAM to the rtpmidi process, and prevents it from being swapped to disk. The use of locked memory (through the mlockall() function call) can be a benefit to realtime applications like MIDI and Audio, but its use can be to the detriment of other processes. So it should be used carefully.

On Ubuntu 18.04 and 20.04 enabling memlock as the default option seemed benign enough. On Ubuntu 20.10, however, this default caused problems. With memlock enabled, the process printed strange errors and aborted. Example:

***MEMORY-ERROR***: rtpmidi[2023]: GSlice: failed to allocate 8176 bytes (alignment: 8192): Cannot allocate memory

Ubuntu 20.10 (Groovy Gorilla) accounts for locked memory pages differently, and even though the memory limit is higher, with all things accounted for, it is not enough.

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