Investigate support for running FDB on systems with 2GB memory

[jessestimpson]

For example: https://forums.foundationdb.org/t/constrained-ram-in-an-application-development-environment/347

Investigate 'smallStorageServer': https://github.com/apple/foundationdb/blob/2e47e97613d36c8d4fdafb5cb2812f689c4a19b6/fdbclient/ServerKnobs.cpp#L884

[jessestimpson]

More: https://forums.foundationdb.org/t/scaling-down-for-small-data-sets/3431/4
https://forums.foundationdb.org/t/what-knobs-should-we-set-to-increase-cache-efficiency/717/5

[jessestimpson]

Note: the cache_memory fdbserver option directly manipulates the page_cache_4k knob:
https://github.com/apple/foundationdb/pull/1889/files

[jessestimpson]

My current understanding is that

1. cache_memory is already controlling page_cache_4k, no action to take there
2. target_storage_bytes_per_server is used in a penalty calculation for load balancing requests coming from the client, so I don't believe it would have any effect on a cluster with exactly 1 fdbserver process
3. ssd-redwood-1 is expected to use more memory than ssd-2. Perhaps it is simply incompatible with such a small system