Re: [PATCH] memcg: remove unneeded preempt_disable

Valdis.Kletnieks
2011-08-18T14:27:23Z

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On Thu, 18 Aug 2011 11:38:00 +0200, Johannes Weiner said:

> Note that on non-x86, these operations themselves actually disable and
> reenable preemption each time, so you trade a pair of add and sub on
> x86
>
> - preempt_disable()
> __this_cpu_xxx()
> __this_cpu_yyy()
> - preempt_enable()
>
> with
>
> preempt_disable()
> __this_cpu_xxx()
> + preempt_enable()
> + preempt_disable()
> __this_cpu_yyy()
> preempt_enable()
>
> everywhere else.

That would be an unexpected race condition on non-x86, if you expected _xxx and
_yyy to be done together without a preempt between them. Would take mere
mortals forever to figure that one out. :)

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