[MLton] Crash fread(...) failed (only read 0) (Cannot allocate memory) during deepFlatten with MLton 20070826

[Matthew Fluet]

On Fri, 18 Apr 2008, Nicolas Bertolotti wrote:
> eof
> fread (0x574e5000, 1, 2000101560, _) failed (only read 0).
>  (Cannot allocate memory)
>
> Looking at the code, I could not figure how this could happen.

It occurs when the runtime system decides to page the heap to disk in 
order to free up virtual memory to reallocate the heap at a larger size.
It will do this if the desired heap size is approaching the physical 
memory limit, even if there is plenty of swap space available on the 
machine.

There is a bug in <src>/runtime/platform/diskBack.unix.c, introduced on 
the x86_64-branch by SVN revision 4642 on 20060711.  That revision 
switched to ANSI C stdio functions, but dropped the lseek in 
diskBack_read.  This means that, when reading back the heap, it begins to 
read from the temporary file with the file position at the end of the 
written heap; that explains why fread failed with EOF.