RFR: 8299915: Remove ArrayAllocatorMallocLimit and associated code [v4]

[Justin King]

On Wed, 11 Jan 2023 14:49:59 GMT, Thomas Stuefe <stuefe at openjdk.org> wrote:

> Curious, I always thought we do ArrayAllocator - using mmap for larger allocations - to prevent memory retention for libc variants whose allocators are "grabby", i.e. which don't promptly return memory to the OS on free(). E.g. because they only use sbrk (Solaris, AIX), or are just cautious about returning memory (glibc).
> 
> Glibc's retention problem is only relevant for fine-grained allocations, so for glibc this is probably fine. This leaves at least AIX as a potential problem. @backwaterred, does the AIX libc malloc() still exclusively use the data segment ? Does free'd memory still stick to the process?
> 
> (While writing this, I remember that we at SAP even rewrote Arena allocation to use mmap for AIX, because large compile arenas caused lasting RSS increase, so it has definitely been a problem in the past)

Correct, glibc always mmap's allocations above a certain limit and always unmaps them on free. I believe most implementations do that, either immediately unmapping or using madvise. AIX still uses sbrk, based on their documentation that I could find. Though AIX does have something called [malloc disclaim](https://www.ibm.com/docs/en/aix/7.2?topic=subsystem-malloc-disclaim).

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PR: https://git.openjdk.org/jdk/pull/11931