On Tue, Jan 29, 2008 at 02:59:14PM +0100, Andrea Arcangeli wrote: > 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.
Ooops my spinlock was gone from the notifier head.... so the above comment is wrong sorry! I thought down_write was needed to serialize against some _external_ event, not to serialize the list updates in place of my explicit lock. The critical section is so small that a semaphore is the wrong locking choice, that's why I assumed it was for an external event. Anyway RCU won't be optimal for a huge flood of register/unregister, I agree the down_write shouldn't create much contention and it saves 4 bytes from each mm_struct, and we can always change it to a proper spinlock later if needed. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
