Re: [PATCH 1/19] MUTEX: Introduce simple mutex implementation

[David Howells <dhowells@redhat.com>]

David Howells <dhowells@redhat.com> wrote:

> > Any reason why you're setting up your own style of waitqueue in
> > mutex-simple.c instead of just using the kernel's style of waitqueue?
> 
> Because I can steal the code from FRV's semaphores or rw-semaphores, and this
> way I can be sure of what I'm doing.

And because:

	struct mutex {
		int			state;
		wait_queue_head_t	wait_queue;
	};

Wastes 8 more bytes of memory than:

	struct mutex {
		int			state;
		spinlock_t		wait_lock;
		struct list_head	wait_list;
	};

on a 64-bit machine if spinlock_t is 4 bytes. Both waste 4 bytes if spinlock_t
is 8 bytes.

David
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