On Tue, Dec 14, 2010 at 10:39:02PM +0800, Wu Fengguang wrote: > On Tue, Dec 14, 2010 at 10:33:25PM +0800, Wu Fengguang wrote: > > 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 > > The log shows that ~64MB reclaimable memory is stoled. But the trace > data only takes 1.8MB. Hmm.. ext2 has the same pattern: http://www.kernel.org/pub/linux/kernel/people/wfg/writeback/tests/3G/ext2-1dd-1M-8p-2952M-2.6.37-rc5+-2010-12-09-01-36/dirty-pages.png But it does not happen for btrfs! http://www.kernel.org/pub/linux/kernel/people/wfg/writeback/tests/3G/btrfs-1dd-1M-8p-2952M-2.6.37-rc5-2010-12-10-21-23/vmstat-dirty.png Seems that it's the nr_slab_reclaimable keep growing until 75s. Looking at http://www.kernel.org/pub/linux/kernel/people/wfg/writeback/tests/3G/ext2-1dd-1M-8p-2952M-2.6.37-rc5+-2010-12-09-01-36/slabinfo-end It should be the buffer heads that slowly eats the memory during the time: buffer_head 670304 670662 104 37 1 : tunables 120 60 8 : slabdata 18117 18126 480 (670304/37)*4 = 72464KB. The consumption seems acceptable for a 3G memory system. Thanks, Fengguang -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom policy in Canada: sign http://dissolvethecrtc.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
