Re: [PATCH] Lightweight userspace semaphores...

[Alan Cox]

> 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.

The shared memory side of it has to be page sized. It doesn't mean you have
to have 1 semaphore per page but it does mean you have to allocate in page
sized chunks for mmu granularity