Messages in this thread | | | Date | Thu, 14 Feb 2019 16:47:41 -0500 | From | Andrea Arcangeli <> | Subject | Re: [PATCH -mm -V7] mm, swap: fix race between swapoff and some swap operations |
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On Thu, Feb 14, 2019 at 04:07:37PM +0800, Huang, Ying wrote: > Before, we choose to use stop_machine() to reduce the overhead of hot > path (page fault handler) as much as possible. But now, I found > rcu_read_lock_sched() is just a wrapper of preempt_disable(). So maybe > we can switch to RCU version now.
rcu_read_lock looks more efficient than rcu_read_lock_sched. So for this purpose in the fast path rcu_read_lock()/unlock() should be the preferred methods, no need to force preempt_disable() (except for debug purposes if sleep debug is enabled). Server builds are done with voluntary preempt (no preempt shouldn't even exist as config option) and there rcu_read_lock might be just a noop.
Against a fast path rcu_read_lock/unlock before the consolidation synchronize_rcu would have been enough, now after the consolidation even more certain that it's enough because it's equivalent to _mult.
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