fix issue 24309 - Memory allocation failed on Azure pipeline

[rainers]

only run GC test that requires 4 GB of memory if that's available as free physical memory

Please note that os_physical_mem() is only used by this test.

[dlang-bot]

Thanks for your pull request, @rainers!

Bugzilla references

Auto-close	Bugzilla	Severity	Description
✓	24309	normal	Memory allocation failed on Azure pipeline

Testing this PR locally

If you don't have a local development environment setup, you can use Digger to test this PR:

dub run digger -- build "stable + dmd#15997"

[kinke]

Thx Rainer for investigating and trying to fix this sporadic issue. 👍

Targeting stable would be nice to improve the situation for just-initiated v2.107.

[rainers]

Targeting stable would be nice to improve the situation for just-initiated v2.107.

Ok, rebased. A merge back to master soon would be much appreciated :)

[kinke]

Oh well, the problem still occurs, but hopefully less often now: https://dev.azure.com/dlanguage/dmd/_build/results?buildId=40448&view=logs&jobId=4eadb322-4cab-54fe-0034-466161775765&j=4eadb322-4cab-54fe-0034-466161775765&t=4bcb94ae-2251-5415-5c2d-f4382a64a161

[rainers]

Oh well, the problem still occurs,

Too bad. Maybe the VM is only a little above the necessary threshold, but cannot assign it to a single allocation. An option could be to add a few GB to it, or just disable the test.

[kinke]

I'm wondering why this was never an issue on Linux, as those runners have 7 GB RAM too. Maybe just vastly more efficient virtual mem allocation on Linux, hardly needing any physical page for that huge, as good as unused allocation?

[rainers]

Maybe just vastly more efficient virtual mem allocation on Linux, hardly needing any physical page for that huge, as good as unused allocation?

I guess it is something like that. Or the Linux VM allows swapping, but the Windows VM does not.

[WalterBright]

Thanks everyone for working hard to resolve this.