Messages in this thread | | | Subject | Re: [PATCH] Inconsistent mmap()/mremap() flags | From | Thayne Harbaugh <> | Date | Tue, 02 Oct 2007 01:06:12 -0600 |
| |
On Tue, 2007-10-02 at 07:15 +0200, Andi Kleen wrote: > On Mon, Oct 01, 2007 at 08:57:10PM -0600, Thayne Harbaugh wrote:
> For mmap you can emulate it by passing a low hint != 0 (e.g. getpagesize()) > in address but without MAP_FIXED and checking if the result is not beyond > your range.
Cool. That's a much better solution for multiple reasons - like you mention, MAP_32BIT is only 2GB as well as it's only available on x86_64.
> > > Given for mremap() it is not that easy because there is no "hint" argument > > > without MREMAP_FIXED; but unless someone really needs it i would prefer > > > to not propagate the hack. If it's really needed it's probably better > > > to implement a start search hint for mremap() > > > > It came up for user-mode Qemu for the case of emulating 32bit archs on > > x86_64 using mmap. At the moment it calls mmap with MAP_32BIT and then > > That would limit the 32bit architectures to 2GB; but their real limit > is 4GB. Losing half of the address space definitely would make users unhappy > (e.g. at least normal Linux kernels wouldn't run at all)
Keeping a kernel happy isn't necessary since it's user-space emulation rather than full emulation. It is, however, useful to have 4GB rather than 2GB.
> Does qemu actually need mremap() ? It would surprise me because > a lot of other OS don't implement it.
Qemu has two modes: full hardware emulation and user-mode emulation. User-mode emulation translates the user-mode code and then remaps the system calls directly into the native kernel (that way all the kernel and all the I/O runs natively and faster). As far as mremap(), I'm trying to get a 32bit arm mremap() emulated syscall mapped onto a 64bit x86_64 mremap().
- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |