RFR: 8338912: CDS: Segmented roots array [v4]

[Ioi Lam]

On Fri, 6 Sep 2024 14:54:21 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

>> src/hotspot/share/cds/archiveHeapWriter.cpp line 219:
>> 
>>> 217:     _buffer_used = oop_offset + bytes_size;
>>> 218:     ensure_buffer_space(_buffer_used);
>>> 219: 
>> 
>> There's a lot of low-level calculation here that's hard to understand. I would suggest splitting this "while" body into smaller functions, something like: 
>> 
>> 
>> while (segment_beg < length) {
>>     int elem_count = MIN2(max_elem_count, length - segment_beg);
>>     objArrayOop segment_oop = allocate_root_segment(elem_count);
>>     for (int i = 0; i < elem_count; i++) {
>>         oop val = roots->at(segment_beg + i);
>>         root_segment_at_put(segment_oop, i, val);
>>     }
>> }
>> 
>> 
>> BTW, I think you can remove the special relocation code in `ArchiveHeapWriter::relocate_embedded_oops` by storing the requested address of `val` into `segment_oop`. You also need to call `mark_oop_pointer()` on each slot.
>
> Helper methods introduced, the code should look cleaner now.
> 
>> I think you can remove the special relocation code in ArchiveHeapWriter::relocate_embedded_oops by storing the requested address of val into segment_oop.
> 
> Comprehension check: this effectively does the relocation right away, right? I can try, but I prefer not to do more than neccessary for segmented root arrays to work :)

Actually my suggestion won't work, because the creation of the root segments are now down before the root objects are copied, so we don't know their requested address yet.

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PR Review Comment: https://git.openjdk.org/jdk/pull/20858#discussion_r1747495092