On Fri, Jul 01, 2022 at 05:33:31PM +0100, David Allsopp wrote:
> This program fails at the second mmap call with EINVAL:
>
> #include <stdio.h>
> #include <sys/mman.h>
> #include <error.h>
>
> int main (void) {
> void * mem;
> /* Reserve 256MB address space for the minor heaps */
> mem = mmap(0, 268439552, PROT_NONE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
> if (mem == MAP_FAILED)
> error(1, 0, "Reservation failed");
> /* Commit the first 2MB heap */
> if (mmap(mem, 2097152, PROT_READ | PROT_WRITE, MAP_PRIVATE |
> MAP_ANONYMOUS | MAP_FIXED, -1, 0) == MAP_FAILED)
> error(1, 0, "Commit failed");
> }
>
> Is this something that's expected to fail for Cygwin, or a bug? The example
> is extracted from OCaml 5.0's runtime, which reserves an area of address
> space and then commits chunks of it as required. The above snippet comes
> from the Linux side, on Windows we're using VirtualAlloc with PAGE_NOACCESS
> to reserve the address space and then VirtualAlloc with MEM_COMMIT and
> PAGE_READWRITE to commit smaller portions of it.
>
> Is there a way to do that with Cygwin's mmap?
Have you tried 'msync()' with MS_ASYNC flag as an alternative approach?
Cheers, Glenn
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