On Tue, Dec 14, 2010 at 09:59:10PM +0800, Wu Fengguang wrote: > On Tue, Dec 14, 2010 at 09:37:34PM +0800, Richard Kennedy wrote: > > As to the ramp up time, when writing to 2 disks at the same time I see > > the per_bdi_threshold taking up to 20 seconds to converge on a steady > > value after one of the write stops. So I think this could be speeded up > > even more, at least on my setup. > > I have the roughly same ramp up time on the 1-disk 3GB mem test: > > http://www.kernel.org/pub/linux/kernel/people/wfg/writeback/tests/3G/ext4-1dd-1M-8p-2952M-2.6.37-rc5+-2010-12-09-00-37/dirty-pages.png > Interestingly, the above graph shows that after about 10s fast ramp up, there is another 20s slow ramp down. It's obviously due the decline of global limit: http://www.kernel.org/pub/linux/kernel/people/wfg/writeback/tests/3G/ext4-1dd-1M-8p-2952M-2.6.37-rc5+-2010-12-09-00-37/vmstat-dirty.png But why is the global limit declining? The following log shows that nr_file_pages keeps growing and goes stable after 75 seconds (so long time!). In the same period nr_free_pages goes slowly down to its stable value. Given that the global limit is mainly derived from nr_free_pages+nr_file_pages (I disabled swap), something must be slowly eating memory until 75 ms. Maybe the tracing ring buffers? free file reclaimable pages 50s 369324 + 318760 => 688084 60s 235989 + 448096 => 684085 http://www.kernel.org/pub/linux/kernel/people/wfg/writeback/tests/3G/ext4-1dd-1M-8p-2952M-2.6.37-rc5+-2010-12-09-00-37/vmstat 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
