If that is the case then maybe it would help to try and allocate memory in the OCaml's runtime by using mmap() directly.

Yes, i need to try this.

Is your application completely single-threaded (since you're using lwt), or do you also use multiple threads?
I think that glibc caches mmap-ed areas even if you free them (i.e. they're still mapped into your process but they might be changed via mprotect() to PROT_NONE), which is especially a problem if you use multiple threads.

Lwt use threads for some bloking system calls, so my application has multiple threads.

Strange behaviour is that the before (first|second) compaction all ocaml memory (1GB) was in mmaped area, but after all ocaml memory in placed in brked memory and later all allocations occurs throught brk. major_heap - is 2MB

Best regards,
--Edwin

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