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    SubjectRe: Inode Lock Scalability V7 (was V6)
    On Fri, Oct 22, 2010 at 01:34:44PM +1100, Nick Piggin wrote:

    > > * walkers of the sb, wb and hash lists can grab ->i_lock at will;
    > > it nests inside their locks.
    > What about if it is going on or off multiple data structures while
    > the inode is live, like inode_lock can protect today. Such as putting
    > it on the hash and sb list.

    Look at the code. You are overengineering it. We do *not* need a framework
    for messing with these lists in arbitrary ways. Where would we need to
    do that to an inode we don't hold a reference to or had placed I_FREEING
    on and would need i_lock held by caller? Even assuming that we need to
    keep [present in hash, present on sb list] in sync (which I seriously doubt),
    we can bloody well grab both locks before i_lock.

    > > 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.

    Code outside of fs/inode.c and fs/fs-writeback.c generally has no business
    looking at the full icache state, period.

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      Last update: 2010-10-22 05:09    [W:0.021 / U:50.100 seconds]
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