freebsd stable - Oct 2020 - mmap and MAP_STACK

Hello.
I have question about mmap.

void *OSMem::AllocateDataArea(size_t &space)
{
    // Round up to an integral number of pages.
    space = (space + pageSize-1) & ~(pageSize-1);
    int fd = -1; // This value is required by FreeBSD.  Linux doesn't care
    int flags = MAP_PRIVATE | MAP_ANON;
#ifdef MAP_STACK
    if (memUsage == UsageStack) flags |= MAP_STACK; // OpenBSD seems to require
this
#endif
    void *result = mmap(0, space, PROT_READ|PROT_WRITE, flags, fd, 0);
    // Convert MAP_FAILED (-1) into NULL
    if (result == MAP_FAILED)
        return 0;
    return result;
}


When MAP_STACK is used, "insufficient memory" error occurs.
When MAP_STACK removed, it is all right.

Please tell me why.

On Wed, Oct 21, 2020 at 04:53:11PM +0300, Nick Kostirya via freebsd-stable
wrote:
> Hello.
> I have question about mmap.
> 
> void *OSMem::AllocateDataArea(size_t &space)
> {
>     // Round up to an integral number of pages.
>     space = (space + pageSize-1) & ~(pageSize-1);
>     int fd = -1; // This value is required by FreeBSD.  Linux doesn't
care
>     int flags = MAP_PRIVATE | MAP_ANON;
> #ifdef MAP_STACK
>     if (memUsage == UsageStack) flags |= MAP_STACK; // OpenBSD seems to
require this
> #endif
>     void *result = mmap(0, space, PROT_READ|PROT_WRITE, flags, fd, 0);
>     // Convert MAP_FAILED (-1) into NULL
>     if (result == MAP_FAILED)
>         return 0;
>     return result;
> }
> 
> 
> When MAP_STACK is used, "insufficient memory" error occurs.
> When MAP_STACK removed, it is all right.
> 
> Please tell me why.
Show ktrace/kdump output of the mmap(2) without and with MAP_STACK.

Or provide a minimal self-contained C source that demonstrates your
issue.