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SubjectRe: 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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