[fpc-devel] RTL: high CPU load in heap manager

[Sergei Gorelkin]

11.11.2014 12:35, Jonas Maebe пишет:
> On 11/11/14 10:28, Adriaan van Os wrote:
>> Jonas Maebe wrote:
>>> On 10/11/14 18:47, Karoly Balogh (Charlie/SGR) wrote:
>>>> It's remove_freed_fixed_chunks(). Can someone explain to me under what
>>>> condition this code is triggered very often and/or could take long to
>>>> execute (there's a loop in there)?
>>>
>>> This was reported earlier too, but I couldn't reproduce it:
>>> http://bugs.freepascal.org/view.php?id=18079 (especially comment 47405
>>> by Sergei).
>>
>> I suggest to use cmem and compare the results.
>>
>> I will also note that malloc uses mremap
>
> None of that would explain the differences experienced in the referred
> bug report, because we don't use mremap-like functionality on any
> platform at this time. The issue there appears to be a corner case that
> makes the heap manager reformat/free/reallocate its internal heap blocks
> all the time on some systems, while on other systems it won't do that
> even though it's presented with exactly the same memory
> allocation/reallocation pattern.
>
This behavior apparently depends on all memory serviced by memory manager, including blocks 
allocated (and maybe also freed) during RTL initialization. That's why it differs between targets, 
and that's why the issue 18079 was no longer reproducible after time. Most probably some (unrelated) 
change was made to RTL initialization code, which also changes the pattern in user code that is 
required to reproduce issue.

Regards,
Sergei