Remove mmapSize check, it has wrong value on ARM64

[yarysh]

In this statement:
mmapAddr, mmapSize, errno := unix.Syscall6(unix.SYS_MREMAP,...)

mmapSize - it is not an allocated size, at least for ARM64 arch.
For ARM64, mmapSize will be equal to the old size.

Example script: https://gist.github.com/yarysh/2b4db19ebe1236f31ff6780d956628f5

I run this script on AMD64 machine with Ubuntu 20.04, and it returns:

Requested size: 20
mmapAddr: 824634507264
mmapSize: 20

And on ARM64 machine (Raspberry PI and AWS Graviton) with Ubuntu 20.04, it returns:

Requested size: 20
mmapAddr: 274878390272
mmapSize: 1024
mremap size mismatch: requested: 20 got: 1024

I have checked man for mremap and it describes returns as:

RETURN VALUE
       On  success mremap() returns a pointer to the new virtual memory area.  On error,
       the value MAP_FAILED (that is, (void *) -1) is returned, and errno is set appropriately.

This issue also affected badger on ARM64: https://discuss.dgraph.io/t/error-mremap-size-mismatch-on-arm64/15333

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[CLAassistant]

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[manishrjain]

Reviewed 1 of 1 files at r1, all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @yarysh)

[awfm9]

@manishrjain could you please release this fix? It has been merged almost half a year ago, and there is still no release with a fix.

[manishrjain]

Hi. I’m no longer maintaining these repos, as I’m no longer with Dgraph Labs. We have fork of this repo that we maintain at outcaste-io. Feel free to file an issue there and we can make a release.