Messages in this thread | | | Date | Thu, 18 Aug 2011 11:38:00 +0200 | From | Johannes Weiner <> | Subject | Re: [PATCH] memcg: remove unneeded preempt_disable |
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On Wed, Aug 17, 2011 at 11:50:53PM -0700, Greg Thelen wrote: > Both mem_cgroup_charge_statistics() and mem_cgroup_move_account() were > unnecessarily disabling preemption when adjusting per-cpu counters: > preempt_disable() > __this_cpu_xxx() > __this_cpu_yyy() > preempt_enable() > > This change does not disable preemption and thus CPU switch is possible > within these routines. This does not cause a problem because the total > of all cpu counters is summed when reporting stats. Now both > mem_cgroup_charge_statistics() and mem_cgroup_move_account() look like: > this_cpu_xxx() > this_cpu_yyy()
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.
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