Messages in this thread | | | Date | Tue, 22 Nov 2011 21:41:55 +0800 | From | Wu Fengguang <> | Subject | Re: [PATCH 3/5] writeback: fix dirtied pages accounting on sub-page writes |
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On Tue, Nov 22, 2011 at 09:07:50PM +0800, Wu Fengguang wrote: > On Tue, Nov 22, 2011 at 08:57:42PM +0800, Peter Zijlstra wrote: > > On Tue, 2011-11-22 at 13:21 +0100, Jan Kara wrote: > > > > + __get_cpu_var(bdp_ratelimits)++; > > > I think you need preempt_disable() and preempt_enable() pair around > > > __get_cpu_var(). Otherwise a process could get rescheduled in the middle of > > > read-modify-write cycle... > > > > there's of course the this_cpu_inc(bdp_ratelimits); thing. > > > > On x86 that'll turn into a single insn, on others it will add the > > required preempt_disable/enable bits. > > It's good to know that. But what if we don't really care which CPU > data it's increasing, and can accept losing some increases due to the > resulted race condition?
I just added a comment for it, hope it helps :)
/* * This is racy, however bdp_ratelimits merely serves as a * gross safeguard. We don't really care the exact CPU it's * charging to and the resulted inaccuracy is acceptable. */ __get_cpu_var(bdp_ratelimits)++;
Thanks, Fengguang
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