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    SubjectRe: Inode Lock Scalability V7 (was V6)
    On Fri, Oct 22, 2010 at 01:34:44PM +1100, Nick Piggin wrote:
    > On Fri, Oct 22, 2010 at 03:20:10AM +0100, Al Viro wrote:
    > > On Fri, Oct 22, 2010 at 11:45:40AM +1100, Nick Piggin wrote:
    > > majority already checks for I_FREEING/I_WILL_FREE, refusing to pick such
    > > inodes. It's not an accidental subtle property of the code, it's bloody
    > > fundamental.
    >
    > I didn't miss that, and I agree that at the point of my initial lock
    > break up, the locking is "wrong". Whether you correct it by changing
    > the lock ordering or by using RCU to do lookups is something I want to
    > debate further.
    >
    > I think it is natural to be able to lock the inode and have it lock the
    > icache state.

    Importantly, to be able to manipulate the icache state in any number of
    steps, under a consistent lock. Exactly like we have with inode_lock
    today.

    Stepping away from that, adding code to handle new concurrencies, before
    inode_lock is able to be lifted is just wrong.

    The locking in my lock break patch is ugly and wrong, yes. But it is
    always an intermediate step. I want to argue that with RCU inode work
    *anyway*, there is not much point to reducing the strength of the
    i_lock property because locking can be cleaned up nicely and still
    keep i_lock ~= inode_lock (for a single inode).


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