Messages in this thread | | | Subject | Re: [RFC][PATCH 3/4] change mnt_writers[] spinlock to mutex | From | Dave Hansen <> | Date | Thu, 10 Jan 2008 11:10:49 -0800 |
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Missed the description on that one. Here it is:
We're shortly going to need to be able to block new mnt_writers for long periods of time during a superblock remount operation. Since this operation can sleep, we can not use a spinlock. We opt for a mutex instead.
This are very, very rarely contented, mostly because they are per-cpu. So, this should be very close to as fast as the spinlocks just with the added benefit that we can sleep while holding them.
We also need to change the get_cpu_var() to use __get_cpu_var() so that we don't disable preemption. Otherwise, we'll be in_atomic() when we try to lock the (sleepable) mutex. We only use the per-cpu data for cache benefits and its per-cpuness is not part of locking logic, so this is OK. _ -- Dave
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