[release/8.0-staging] improve distribute_free_regions

[mangod9]

Port change for better free-list management. This is a back port of #109431

Customer Impact

• Customer reported
• Found internally

Memory utilization regression as part of Regions Enablement. Reported by a customer here: #103582.
The fix is to improve distribute_free_regions where aged regions are added to decommit list to ultimately free.

Regression

• Yes
• No

Yes in memory utilization. For certain customers who were running with dense containers they would observe an OOM occasionally.

Testing

Verified with internal performance testing. Provided a private to the customer to try out and they confirmed their memory utilization improved after the fix.

Risk

Low, this only impacts how free regions are deallocated.

[Copilot]

Pull Request Overview

This PR ports distributed free list functionality from .NET 10 and adjusts related GC region management constants.

• Updates the enum free_region_kind with new indices to support distributed free regions.
• Adds new GC heap methods for distributing and manipulating free regions.
• Introduces distinct decommit age thresholds for basic, large, and huge free regions.

[dotnet-policy-service]

Tagging subscribers to this area: @dotnet/gc
See info in area-owners.md if you want to be subscribed.

[Maoni0]

in distribute_free_regions

if (settings.reason == reason_induced_aggressive)
{

so this is not from Mark's change but a separate PR: #96513 that I think we should include this line in this if block -

global_regions_to_decommit[huge_free_region].transfer_regions (&global_free_huge_regions);

---

Refers to: src/coreclr/gc/gc.cpp:13342 in 40807e6. [](commit_id = 40807e6, deletion_comment = False)

[Maoni0]

you might as well change this in decide_on_decommit_strategy

size_t decommit_step_milliseconds = min (ephemeral_elapsed, (10 * 1000));

to
size_t decommit_step_milliseconds = min (ephemeral_elapsed, (size_t)(10 * 1000));
in `distribute_freesame as in .net 9 and 10

---

Refers to: src/coreclr/gc/gc.cpp:13841 in 40807e6. [](commit_id = 40807e6, deletion_comment = False)

[Maoni0]

LGTM!

[jeffschwMSFT]

lgtm. we will take for consideration in 8.0.x