Re: cross-bounday memory communication b/w user app and the Kernel.How?
Re: cross-bounday memory communication b/w user app and the Kernel.How?
- Subject: Re: cross-bounday memory communication b/w user app and the Kernel.How?
- From: Andrew Gallatin <email@hidden>
- Date: Fri, 2 Jun 2006 15:45:39 -0400 (EDT)
Terry Lambert writes:
> are different address spaces. Unlike most 32 bit OS's intended to
> operate on small machines, MacOS X does not map the user process
> address space into the kernel address space, so a direct copy is not
> possible for a user space buffer when you are operating in kernel
> space (or vice versa - which is not possible even on OS's that map
> process in, since they don't map the kernel out into user land). The
> benefit of doing this is that instead of having only 2G or 3G for your
> programs, you get the full 4G. It also means that instead of only
> having 2G or 1G for the kernel's use, you have the full 4G - that
> effectively means that the kernel can do a lot more housekeeping in
> its own memory, and can theerefore run on machines with large amounts
> of physical memory (8G, 16G, etc.) without running out of address space.
The downside of this is that things like syscalls take about 8x long
as linux on the same hardware the last time I measured them.
Drew
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