[Haskell-cafe] GHC FreeBSD memory model (was: 8.4.3 release)

[Viktor Dukhovni]

On Thu, Jul 05, 2018 at 08:13:33PM -0400, Viktor Dukhovni wrote:
> On Thu, Jul 05, 2018 at 09:32:31AM -0400, Ben Gamari wrote:
> 
> > We use a much different memory allocation strategy on FreeBSD which
> > (AFAIK) does not allow one to reserve address space without also
> > committing.
> 
> Here's a demo of mapping in a 1TB heap on FreeBSD 11.1, on a machine
> with "just" 64GB of RAM and 160GB swap.  I would expect anon memory
> mappings to behave similarly on older systems.
> 
>     $ cat foo.c
>     #include <stdio.h>
>     #include <stdlib.h>
>     #include <unistd.h>
>     #include <sys/mman.h>
> 
>     int main(int argc, char **argv)
>     {
> 	size_t heaplen = 1ULL << 40; /* 1TB */
> 	unsigned char *heap;
> 
> 	heap = mmap(NULL, heaplen, PROT_READ|PROT_WRITE, MAP_ANON, -1, 0);
> 	heap[0] = 'A';
> 	heap[heaplen-1] = 'z';
> 	printf ("%p(%zd) %c %c\n", heap, heaplen, heap[0], heap[heaplen-1]);
> 	sleep(2);
> 	return 0;
>     }

I also get essentially the same results with posix_memalign(3):

    #include <stdlib.h>
    #include <stdio.h>
    #include <err.h>
    #include <unistd.h>
    #include <sys/mman.h>

    int main(int argc, char **argv)
    {
	size_t heaplen = 1ULL << 40;
	void *p;
	unsigned char *heap;

	if (posix_memalign(&p, getpagesize(), heaplen) != 0)
	    err(1, "posix_memalign");
	heap = p;
	heap[0] = 'A';
	heap[heaplen-1] = 'z';
	printf ("%p(%zd) %c %c\n", heap, heaplen, heap[0], heap[heaplen-1]);
	sleep(2);
	return 0;
    }

    $ ./foo & sleep 1; ps -o vsz= -o rss= $! ; wait
    [1] 76003
    0x801000000(1099511627776) A z
    1073750140 2080
    [1]+  Done                    ./foo

-- 
	Viktor.