Decrease memory footprint of JVM-based apps by setting MALLOC_ARENA_MAX

[giner]

Set MALLOC_ARENA_MAX to 2 by default and introduce environment variable SPLICE_MALLOC_ARENA_MAX as an option to override this value. This can decrease resident memory footprint for JVM process reduce unnecessary OOM kills by the OS.

Here are the details:

• By default on 64-bit systems the limit for number of arenas in glibc malloc is determined as 8 * num_of_cores (in our case it is the max arenas becomes 8 *16 = 128)
• Container limits are not respected
• Each Arena allocates one heap of 64 MiB at the time of creation
• A new Arena is created each time when malloc is called and all existing Arenas are locked by other threads
• JVM based software tends to create a lot of threads, at the same time it has it's own memory management so it doesn't call malloc frequently. Memory waste from a large number of arenas is quite significant on machines with many physical cores and this waste is especially noticeable in smaller apps.