[GC] Handle growing global_regions_to_decommit lists #106168
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) In #105521, the number of regions to be decommitted can be reduced, but the budgets weren't updated to include the new regions. This was fine for huge regions, which just sit in the global free list anyway, and it (sort of) works in release builds (though some regions may end up decommitted anyway if they are still in the surplus list at the end of distribution), but it isn't the intended behavior and can trigger a debug assertion that the surplus list is empty. This change (a subset of #106168), restructures distribute_free_regions so that instead of "decommit or adjust budgets", we first decommit and adjust the remaining balance. Then we adjust budgets based on the new value.
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In some cases, we can add items to the decommit list faster that we're willing to decommit them. Decommit is throttled to avoid potentially long pauses. In these cases, instead of continuing to add items to the decommit list, we can artificially inflate our budgets since the memory is already committed.
One advantage of this fix late in the product cycle is that it only changes behavior if the decommit list is non-empty at the start of a GC. A disadvantage is that capping the new decommit list at the size of the previous amount decommitted is fairly arbitrary and doesn't account for differing times between GCs. We could use different amounts or try to track more history, but also an incorrect amount will just lead to more/less memory on the decommit list until it is recalculated at the next GC anyway.
This also imposes an absolute cap on the decommit list size.
This is an alternate fix to #87715