RFR: 8366155: Serial: Obsolete PretenureSizeThreshold

[Albert Mingkun Yang]

On Tue, 26 Aug 2025 12:51:21 GMT, Francesco Andreuzzi <duke at openjdk.org> wrote:

>> Remove obj-size checking before young/old-gen allocation -- an allocation succeeds iff there is enough free space.
>> 
>> This simplifies the allocation logic:
>> 1. before attempting gc: `mem_allocate_work` does young-gen allocation then old-gen-no-expansion allocation
>> 2. after gc (still inside gc safepoint): `satisfy_failed_allocation` does young-gen allocation old-gen-with-expansion allocation
>> 
>> Test: tier1-3
>
> src/hotspot/share/gc/serial/serialHeap.cpp line 286:
> 
>> 284: 
>> 285: HeapWord* SerialHeap::expand_heap_and_allocate(size_t size, bool is_tlab) {
>> 286:   HeapWord* result = _young_gen->allocate(size);
> 
> The order of `_young_gen->allocate` and `old_gen->expand_and_allocate` is reversed now. It used to be `_old_gen->expand_and_allocate == nullptr --> _young_gen->allocate`, now it's the other way around. Is that intended?

On master, before the method is invoked, young-gen allocation is already attempted inside `attempt_allocation(size, is_tlab, false /*first_only*/);`.

With this cleanup, it become clearer that we try young-gen first, then old-gen. So, yes, this is intended.

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PR Review Comment: https://git.openjdk.org/jdk/pull/26941#discussion_r2301014403