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* [Caml-list] Only bytecode version of executable allocating huge amounts
@ 2019-05-28 11:32 Jon French
  2019-05-28 16:49 ` rixed
                   ` (2 more replies)
  0 siblings, 3 replies; 6+ messages in thread
From: Jon French @ 2019-05-28 11:32 UTC (permalink / raw)
  To: caml-list


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Hi all,

I'm wondering if anyone on this list might have encountered this issue before, since it's got me pretty stumped.

We have an OCaml project ( https://github.com/rems-project/sail ) which tries to allocate huge amounts of memory, but only when compiled to bytecode. The native version works perfectly fine.

strace for an example run ends in:

> openat(AT_FDCWD, "/home/ojno/work/sail2/lib/vector_dec.sail", O_RDONLY|O_CLOEXEC) = 3
> lseek(3, 0, SEEK_CUR) = 0
> read(3, "$ifndef _VECTOR_DEC\n$define _VEC"..., 65536) = 7031
> mmap(NULL, 1965819695104, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = -1 ENOMEM (Cannot allocate memory)
> brk(0x5729f32c4000) = 0x55603f2f4000
> mmap(NULL, 1965819826176, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = -1 ENOMEM (Cannot allocate memory)
> write(2, "Fatal error: out of memory.\n", 28Fatal error: out of memory.
> ) = 28
> exit_group(2) = ?
> +++ exited with 2 +++

which naturally fails since I don't have 2 TB of memory available. 

The exact amount of the allocation varies from input to input and even run to run, but is always that approximate size. There's no characteristic pattern of heap or stack running out of control if I turn on memory debugging info in $OCAMLRUNPARAM, just that one huge allocation. When run in ocamldebug, it also doesn't appear to be failing at a location which is sensible to be allocating such amounts of memory -- and the location also varies with the input. And on tiny inputs it doesn't seem to try and make the allocation at all.

Are we actually seeing a compiler/runtime bug here? Is there something I'm missing?

Thanks,

Jon French
Computer Laboratory
University of Cambridge

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Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2019-05-28 11:32 [Caml-list] Only bytecode version of executable allocating huge amounts Jon French
2019-05-28 16:49 ` rixed
2019-05-28 17:16 ` Xavier Leroy
2019-05-28 17:23 ` Ivan Gotovchits
2019-05-28 17:58   ` Fabrice Le Fessant
2019-05-29 15:22     ` Jon French

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