Why doesn't Linux have a NORCU RCU option that just implements the RCU API as plain rwlocks?
That's unfortunate. The "copy" part of RCU seems to make the whole kernel OOM-unsafe and prob. frag-unsafe for nommu.
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TREE_RCU "..is designed for very large SMP system with hundreds or thousands of CPUs...also scales down nicely.." No.
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Why does everybody love breaking the important real-world case (1-8 cores) for the sake of HPC wackiness? :-(
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Lots of important real-world cases with a wide range of CPUs. You are doing mobile or some such?
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Mobile and embedded. But even for reasonable desktop and server use locks are better.
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But I don't think this is solvable in Linux. The code using the RCU api actually does the alloc/free operations...
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...so there's no way a "NORCU" (as plain rwlock) could give you update-in-place without unwanted invasive changes.
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That is correct. A NORCU has the same problem in user mode in the presence of signal handlers.
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That's trivial to solve in kernel because disabling irqs takes at most a couple cycles. OTOH sigprocmask is syscall.
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Ummm... Compared to immediate self-deadlock via interrupt for your NORCU? RCU has anti-OOM-unsafe code as well.
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