Re: next meeting: Monday Feb 10, 10:00 - 12:00 CET

[pierre.alain@xxxxxxx]

Jan 30, 2025, 11:10 by hannes@xxxxxxxxxxx:

> On 27/01/2025 10:37, Reynir Björnsson wrote:
>
>> ### GC compactor
>> - The GC compactor will unmap _ leading to ABORT
>> - As you have to call the compactor explicitly we probably did not test it
>> - Maybe we don't actually need compaction?
>> - Sam: Observeration from mirage-www:
>>    - the behavior was similar to ocaml 4 version
>>    - if we tweak space overhead to 80 we get a similar profile as ocaml 4 
>> version
>> - Pierre: we can't deny users to call `Gc.compact ()` which would lead to a 
>> crash
>> - Pierre: implementing mmap/munmap would be a huge effort
>>
>
>
> Is this true? If I understand it correctly, we support mmap (with off = 0 and 
> flags = MAP_ANONYMOUS) already -- which is basically malloc & zeroing out the 
> memory.
>
> In this scenario, isn't munmap (of that previously mmap()ed area) just a 
> free()?
>
>
Dear Hannes,

Yes, munmap an entire mmapped region is equivalent to free, and that's our 
current implementation.
My understanding of the issue was to munmap of a chunk inside an mmapped 
region, which requires a full mmap/munmap implementation (we don't have 
currently). I'm not sure where the code that causes the ABORT lives and maybe 
it can be difficult to trigger the situation?

Best,
Pierre