Re: WARNING in __mmdrop

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On 2019/7/25 下午9:26, Michael S. Tsirkin wrote:
Exactly, and that's the reason actually I use synchronize_rcu() there.

So the concern is still the possible synchronize_expedited()?
I think synchronize_srcu_expedited.

synchronize_expedited sends lots of IPI and is bad for realtime VMs.

Can I do this
on through another series on top of the incoming V2?

Thanks

The question is this: is this still a gain if we switch to the
more expensive srcu? If yes then we can keep the feature on,


I think we only care about the cost on srcu_read_lock() which looks pretty tiny form my point of view. Which is basically a READ_ONCE() + WRITE_ONCE().

Of course I can benchmark to see the difference.


if not we'll put it off until next release and think
of better solutions. rcu->srcu is just a find and replace,
don't see why we need to defer that. can be a separate patch
for sure, but we need to know how well it works.


I think I get here, let me try to do that in V2 and let's see the numbers.

Thanks




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