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    SubjectRe: [patch 1/4] spinlock: lockbreak cleanup
    On Thu, 2007-11-01 at 15:29 +0100, Nick Piggin wrote:
    > On Thu, Nov 01, 2007 at 03:06:05PM +0100, Peter Zijlstra wrote:
    > > On Thu, 2007-11-01 at 15:02 +0100, Nick Piggin wrote:
    > >
    > > > Rename need_lockbreak to spin_needbreak, make it use spin_is_contended to
    > > > decouple it from the spinlock implementation, and make it typesafe (rwlocks
    > > > do not have any need_lockbreak sites -- why do they even get bloated up
    > > > with that break_lock then?).
    > >
    > > IIRC Lee has a few patches floating about that do introduce lockbreak
    > > stuff for rwlocks.
    > Well that would be a good reason to introduce a break_lock for them,
    > but previously not so much... we have rwlocks in some slightly space
    > critical structures (vmas, inodes, etc).
    > I guess it was done to make the "template" hacks eaiser. I don't really
    > find that in good taste, especially for important core infrastructure.
    > Anyway.

    Actually, what I had/have is a cond_resched_rwlock() that I needed to
    convert the i_mmap_lock() to rw for testing reclaim scalability. [I've
    seen a large system running an Oracle OLTP load hang spitting "cpu soft
    lockup" messages with all cpus spinning on a i_mmap_lock spin lock.]
    One of the i_mmap_lock paths uses cond_resched_lock() for spin locks.
    To do a straight forward conversion [and maybe that isn't the right
    approach], I created the cond_resched_rwlock() function by generalizing
    the cond_sched_lock() code and creating both spin and rw lock wrappers.
    I took advantage of the fact that, currently, need_lockbreak() is a
    macro and that both spin and rw locks have/had the break_lock member.
    Typesafe functions would probably be preferrable, if we want to keep
    break_lock for rw spin locks.

    Here's the most recent posting:

    See the changes to sched.[ch]. Should apply to 23-mm1 with offsets and
    minor fixup in fs/inode.c.


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