Re: [Caml-list] Only bytecode version of executable allocating huge amounts

[rixed@happyleptic.org]

Can it be another instance of https://github.com/ocaml/opam/issues/3636 ?

On Tue, May 28, 2019, at 14:27, Jon French wrote:
> 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