On Fri, Sep 02, 2011 at 12:29:50AM +0800, Jan Kara wrote: > On Thu 01-09-11 22:40:41, Wu Fengguang wrote: > > Peter, > > > > This is an amazing bug. I'm not sure how the accounting goes wrong in > > some tricky way. But you can compare the exact bdi proportions pattern > > before/after patch. The gray "bdi setpoint" lines are vastly different. > > > > --- > > When increasing BDI_WRITTEN together with bdi->completions inside the > > same local irq disabling block, bdi_thresh is found to go wild in the > > 1 disk + 1 usb stick writeback test case. Fix it by moving BDI_WRITTEN > > accounting out. > I don't understand this - the patch is just NOP. The change in > test_clear_page_writeback() does absolutely nothing and the change in > bdi_writeout_inc() just changes: > local_irq_save(flags); > __inc_bdi_stat(bdi); > __prop_inc_percpu_max(&vm_completions, &bdi->completions, > bdi->max_prop_frac); > local_irq_restore(flags); > > to: > local_irq_save(flags); > __inc_bdi_stat(bdi); > local_irq_restore(flags); > local_irq_save(flags); > __prop_inc_percpu_max(&vm_completions, &bdi->completions, > bdi->max_prop_frac); > local_irq_restore(flags); > > So the difference must be in something else... Yes you are right -- this patch is basically a NOP. I retried without this patch and it's now working fine again. Something mysterious to catch.. 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
