> On Mon, Feb 25, 2002 at 04:39:56PM +0000, Alan Cox wrote:
> > _alloca
> > mmap
> >
> > Still fits on the stack 8)
>
> Are we sure that forcing semaphore overhead to the size of a page is a
> good idea? I'd much rather see a sleep/wakeup mechanism akin to wait
> queues be exported by the kernel so that userspace can implement a rich
> set of locking functions on top of that in whatever shared memory is
> being used.
Unfortunately, no. You need to know what userspace is using them for so
you can check to avoid the "add to waitqueue" race.
AFAICT a mutex is the simplest useful primitive that can be realistically
exported.
Hope that helps,
Rusty.
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