RFR: 8307058: Implementation of Generational ZGC [v6]

[Stefan Karlsson]

On Mon, 8 May 2023 10:19:44 GMT, Fei Yang <fyang at openjdk.org> wrote:

>> Could you provide the values for `reserved`, `ZAddressHeapBase`, and `ZAddressOffsetMax`, when this test is failing. I'd like to know if we can make a workaround for you, or if we have to turn off the test for riscv.
>
> @stefank : I ran this gtest for 5 times on linux-riscv64 board and here is what I got.
> 
> ZAddressHeapBase :     0x800000000
> ZAddressOffsetMax:     0x800000000
> ZGranuleSize          :     0x200000
> 
> In os::pd_attempt_reserve_memory_at() which is called by os::attempt_reserve_memory_at(), return value by anon_mmap() [1] is one of: ```0x3f8d5ff000, 0x3f649fe000, 0x3f5d3ff000, 0x3f68077000 and 0x3f555ff000```
> 
> So seems that those values are not in the range [ZAddressHeapBase, ZAddressHeapBase+ZAddressOffsetMax).
> 
> [1] https://github.com/openjdk/jdk/blob/master/src/hotspot/os/linux/os_linux.cpp#L3334

That's unfortunate. Could you try this patch, which probes the address range to see if it can reserve the memory somewhere else within `[ZAddressHeapBase, ZAddressHeapBase+ZAddressOffsetMax)`:
https://github.com/stefank/jdk/tree/zgc_generational_review_test_zforwarding

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PR Review Comment: https://git.openjdk.org/jdk/pull/13771#discussion_r1187406599