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    SubjectRe: [patch 09/10] SLUB: Do our own locking via slab_lock and slab_unlock.
    On Sun, 28 Oct 2007, Pekka J Enberg wrote:

    > It would be easier to review the actual locking changes if you did the
    > SlabXXX removal in a separate patch.

    There are no locking changes.

    > > -static __always_inline void slab_lock(struct page *page)
    > > +static __always_inline void slab_unlock(struct page *page,
    > > + unsigned long state)
    > > {
    > > - bit_spin_lock(PG_locked, &page->flags);
    > > + smp_wmb();
    >
    > Memory barriers deserve a comment. I suppose this is protecting
    > page->flags but against what?

    Its making sure that the changes to page flags are made visible after all
    other changes.

    >
    > > + page->flags = state;
    > > + preempt_enable();
    >
    > We don't need preempt_enable for CONFIG_SMP, right?

    preempt_enable is needed if preemption is enabled.

    >
    > > + __release(bitlock);
    >
    > This needs a less generic name and maybe a comment explaining that it's
    > not annotating a proper lock? Or maybe we can drop it completely?

    Probably.

    > > +static __always_inline unsigned long slab_trylock(struct page *page)
    > > +{
    > > + unsigned long state;
    > > +
    > > + preempt_disable();
    > > + state = page->flags & ~LOCKED;
    > > +#ifdef CONFIG_SMP
    > > + if (cmpxchg(&page->flags, state, state | LOCKED) != state) {
    > > + preempt_enable();
    > > + return 0;
    > > + }
    > > +#endif
    >
    > This is hairy. Perhaps it would be cleaner to have totally separate
    > functions for SMP and UP instead?

    I think that is reasonably clear. Having code duplicated is not good
    either. Well we may have to clean this up a bit.



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