RFR: 8301404: Factor out os::malloc with os::realloc common code, so that we only have 1 code path [v8]

[Gerard Ziemski]

On Tue, 1 Apr 2025 12:51:03 GMT, Gerard Ziemski <gziemski at openjdk.org> wrote:

>> This is the 2nd time I am proposing this (controversial?) change, but this time I do have performance numbers, which indicate no change in speed (using NMTBenchmark from #23786):
>> 
>> proposed:
>> 
>> time:72,642,827[ns]
>> [samples:807,804] [NMT headers:382,064]
>> [malloc#:588,703] [realloc#:12,462] [free#:206,639]
>> memory requested:57,274,288 bytes, allocated:69,004,800 bytes
>> malloc overhead:4,853,360 bytes [8.47%], NMT headers overhead:6,877,152 bytes [12.01%]
>> existing code:
>> 
>> time:73,085,446[ns]
>> [samples:807,804] [NMT headers:382,064]
>> [malloc#:588,703] [realloc#:12,462] [free#:206,639]
>> memory requested:57,274,288 bytes, allocated:69,004,800 bytes
>> malloc overhead:4,853,360 bytes [8.47%], NMT headers overhead:6,877,152 bytes [12.01%]
>> Note: the NMTBenchmark reports realloc(nullptr) as mallocs(), which is why both versions show the same count for mallocs/reallocs.
>> 
>> The performance is virtually the same where I sampled each test 30 times and took the best (the shortest).
>> 
>> This proposed change factors out the common code and simplifies both os::malloc and os::realloc. We were able to reduce malloc from 44 lines down to 8 (saving of 36 lines) and realloc from 84 to 55 (29 lines).
>> 
>> To me the most important part here is that we reduce the number of times that NMT has to interact with the native allocation code.
>
> Gerard Ziemski has updated the pull request incrementally with one additional commit since the last revision:
> 
>   revert last checkin - wrong issue

Thank you for the review Coleen, unfortunately this looks like a dead end, since Johan and Stefan do not see this as an improvement. Stefan has suggested an alternate impl, which does clean up things nicely, even though it does not address at all my concerns and reasons for working on this fix.

Is that correct? Johan, Stefan, you are NO on this?

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PR Comment: https://git.openjdk.org/jdk/pull/24189#issuecomment-2769364553