On Tue, Nov 22, 2011 at 08:48:11PM +0800, Jan Kara wrote: > On Tue 22-11-11 20:30:01, Wu Fengguang wrote: > > > > @@ -1743,6 +1738,8 @@ void account_page_dirtied(struct page *p > > > > __inc_bdi_stat(mapping->backing_dev_info, BDI_DIRTIED); > > > > task_dirty_inc(current); > > > > task_io_account_write(PAGE_CACHE_SIZE); > > > > + current->nr_dirtied++; > > > > + __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... > > > > Hmm, I'm not worried about it at all, because bdp_ratelimits don't > > need to be accurate. In normal cases it won't even trigger one single > > call to balance_dirty_pages(). > I agree regarding the accuracy. But the CPU can change when the process > is scheduled again. So you could modify counter of a CPU you are not > running on. And that can cause bad things... Will modifying another CPU's per-cpu data lead to more serious problems than inaccuracy? If not, it would be fine. bdp_ratelimits is only meant to be a coarse grained safeguard after all :-) > > btw, account_page_dirtied() is called inside spinlock, will it be > > sufficient? > Currently it is not enough in real-time kernels and when sleeping > spinlocks work gets merged it won't be enough even in standard kernels... > And in kernels where spinlock means preemption is disabled > preempt_enable/disable will be almost for free... I see, spinlock won't be a general superset of preempt_enable/disable indeed. Thanks, Fengguang -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
