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    SubjectRe: [patch 1/6] mmu_notifier: Core code
    On Mon, Jan 28, 2008 at 12:28:41PM -0800, Christoph Lameter wrote:
    > +struct mmu_notifier_head {
    > + struct hlist_head head;
    > +};
    > +
    > struct mm_struct {
    > struct vm_area_struct * mmap; /* list of VMAs */
    > struct rb_root mm_rb;
    > @@ -219,6 +223,8 @@ struct mm_struct {
    > /* aio bits */
    > rwlock_t ioctx_list_lock;
    > struct kioctx *ioctx_list;
    > +
    > + struct mmu_notifier_head mmu_notifier; /* MMU notifier list */
    > };

    Not sure why you prefer to waste ram when MMU_NOTIFIER=n, this is a
    regression (a minor one though).

    > + /*
    > + * lock indicates that the function is called under spinlock.
    > + */
    > + void (*invalidate_range)(struct mmu_notifier *mn,
    > + struct mm_struct *mm,
    > + unsigned long start, unsigned long end,
    > + int lock);
    > +};

    It's out of my reach how can you be ok with lock=1. You said you have
    to block, if you can deal with lock=1 once, why can't you deal with
    lock=1 _always_?

    > +/*
    > + * Note that all notifiers use RCU. The updates are only guaranteed to be
    > + * visible to other processes after a RCU quiescent period!
    > + */
    > +void __mmu_notifier_register(struct mmu_notifier *mn, struct mm_struct *mm)
    > +{
    > + hlist_add_head_rcu(&mn->hlist, &mm->mmu_notifier.head);
    > +}
    > +EXPORT_SYMBOL_GPL(__mmu_notifier_register);
    > +
    > +void mmu_notifier_register(struct mmu_notifier *mn, struct mm_struct *mm)
    > +{
    > + down_write(&mm->mmap_sem);
    > + __mmu_notifier_register(mn, mm);
    > + up_write(&mm->mmap_sem);
    > +}
    > +EXPORT_SYMBOL_GPL(mmu_notifier_register);

    The down_write is garbage. The caller should put it around
    mmu_notifier_register if something. The same way the caller should
    call synchronize_rcu after mmu_notifier_register if it needs
    synchronous behavior from the notifiers. The default version of
    mmu_notifier_register shouldn't be cluttered with unnecessary locking.


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