Linux Operating System Source Code: IBM Patches

There were three global locks in IPC, one per type.  To reduce the lock
contention, I have provided a patch which breaks down the global lock into one
lock per ID.  But, we still need a rw lock to protect the IPC ID array resizing.
 We first used a rw lock. But by doing so added another layer of lock and may
cause cacheline bouncing.

RCU core code was got in 2.5.43 kernel, thus provide a way(by using RCU) to
breaks down IPC locks without adding a new layer of rw lock.

Now IPC ID array resizing is lock free.  We also extended the use of RCU in
ipc_rmid() to postpone the real free of a IPC ID until nobody is refering it. 
By doing so is to prevent ipc_lock() returning an invalid IPC ID.

The latest patch could be found in sf.net/projects/lse

This patch is depend on ReadCopyUpdate core patchs(in mainline kernel since
2.5.43), which is also avaliable from sf.net/projects/lse