Messages in this thread | | | Date | Wed, 14 May 2008 08:18:21 -0700 (PDT) | From | Linus Torvalds <> | Subject | Re: [PATCH 08 of 11] anon-vma-rwsem |
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On Wed, 14 May 2008, Robin Holt wrote: > > Are you suggesting the sending side would not need to sleep or the > receiving side?
One thing to realize is that most of the time (read: pretty much *always*) when we have the problem of wanting to sleep inside a spinlock, the solution is actually to just move the sleeping to outside the lock, and then have something else that serializes things.
That way, the core code (protected by the spinlock, and in all the hot paths) doesn't sleep, but the special case code (that wants to sleep) can have some other model of serialization that allows sleeping, and that includes as a small part the spinlocked region.
I do not know how XPMEM actually works, or how you use it, but it seriously sounds like that is how things *should* work. And yes, that probably means that the mmu-notifiers as they are now are simply not workable: they'd need to be moved up so that they are inside the mmap semaphore but not the spinlocks.
Can it be done? I don't know. But I do know that I'm unlikely to accept a noticeable slowdown in some very core code for a case that affects about 0.00001% of the population. In other words, I think you *have* to do it.
Linus
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