On Fri, Mar 04, 2011 at 04:48:27AM +0800, Vivek Goyal wrote: > On Thu, Mar 03, 2011 at 03:12:26PM -0500, Vivek Goyal wrote: > > On Thu, Mar 03, 2011 at 02:45:05PM +0800, Wu Fengguang wrote: > > > > [..] > > > - serve as simple IO controllers: if provide an interface for the user > > > to set task_bw directly (by returning the user specified value > > > directly at the beginning of dirty_throttle_bandwidth(), plus always > > > throttle such tasks even under the background dirty threshold), we get > > > a bandwidth based per-task async write IO controller; let the user > > > scale up/down the @priority parameter in dirty_throttle_bandwidth(), > > > we get a priority based IO controller. It's possible to extend the > > > capabilities to the scope of cgroup, too. > > > > > > > Hi Fengguang, > > > > Above simple IO controller capabilities sound interesting and I was > > looking at the patch to figure out the details. > > > > You seem to be mentioning that user can explicitly set the upper rate > > limit per task for async IO. Can't really figure that out where is the > > interface for setting such upper limits. Can you please point me to that. > > Never mind. Jeff moyer pointed out that you mentioned above as possible > future enhancements on top of this patchset. Hi Vivek, Here is an update show the bandwidth limit possibility. I tested it by starting 8 or 10 concurrent dd's, doing "ulimit -m $((i<<10))" before starting the i'th dd. The first 3 dd's progress are shown in the following graphs. http://www.kernel.org/pub/linux/kernel/people/wfg/writeback/dirty-throttling-v6/BW-LIMIT/xfs-10dd-1M-8p-2975M-20%25-2.6.38-rc7-dt6+-2011-03-04-16-22/balance_dirty_pages-task-bw.png http://www.kernel.org/pub/linux/kernel/people/wfg/writeback/dirty-throttling-v6/BW-LIMIT/xfs-8dd-1M-8p-2975M-20%25-2.6.38-rc7-dt6+-2011-03-04-16-15/balance_dirty_pages-task-bw.png http://www.kernel.org/pub/linux/kernel/people/wfg/writeback/dirty-throttling-v6/BW-LIMIT/ext4-10dd-1M-8p-2975M-20%25-2.6.38-rc7-dt6+-2011-03-04-16-29/balance_dirty_pages-task-bw.png http://www.kernel.org/pub/linux/kernel/people/wfg/writeback/dirty-throttling-v6/BW-LIMIT/btrfs-10dd-1M-8p-2975M-20%25-2.6.38-rc7-dt6+-2011-03-04-16-35/balance_dirty_pages-task-bw.png The bandwidth limit is not perfect in two of the above cases: - the xfs 10dd case: tasks could be hard throttled on dirty exceeding - the ext4 10dd case: filesystem makes >500ms latencies (smaller ones will be compensated) Thanks, Fengguang --- Subject: writeback: per-task async write bandwidth limit Date: Fri Mar 04 10:38:04 CST 2011 XXX: the user interface is reusing RLIMIT_RSS for now. CC: Vivek Goyal <vgoyal@xxxxxxxxxx> CC: Andrea Righi <arighi@xxxxxxxxxxx> Signed-off-by: Wu Fengguang <fengguang.wu@xxxxxxxxx> --- mm/page-writeback.c | 20 ++++++++++++++++---- 1 file changed, 16 insertions(+), 4 deletions(-) --- linux-next.orig/mm/page-writeback.c 2011-03-04 10:33:06.000000000 +0800 +++ linux-next/mm/page-writeback.c 2011-03-04 16:03:52.000000000 +0800 @@ -428,6 +428,11 @@ unsigned long bdi_dirty_limit(struct bac return bdi_dirty; } +static unsigned long hard_dirty_limit(unsigned long thresh) +{ + return max(thresh, default_backing_dev_info.dirty_threshold); +} + /* * If we can dirty N more pages globally, honour N/8 to the bdi that runs low, * so as to help it ramp up. @@ -589,7 +594,7 @@ static unsigned long dirty_throttle_band unsigned long bdi_dirty, struct task_struct *tsk) { - unsigned long limit = default_backing_dev_info.dirty_threshold; + unsigned long limit = hard_dirty_limit(thresh); unsigned long bdi_thresh = bdi->dirty_threshold; unsigned long origin; unsigned long goal; @@ -1221,6 +1226,11 @@ static void balance_dirty_pages(struct a * when the bdi limits are ramping up. */ if (nr_dirty <= (background_thresh + dirty_thresh) / 2) { + if (current->signal->rlim[RLIMIT_RSS].rlim_cur != + RLIM_INFINITY) { + pause_max = MAX_PAUSE; + goto calc_bw; + } current->paused_when = jiffies; current->nr_dirtied = 0; break; @@ -1233,7 +1243,7 @@ static void balance_dirty_pages(struct a bdi_start_background_writeback(bdi); pause_max = max_pause(bdi, bdi_dirty); - +calc_bw: bw = dirty_throttle_bandwidth(bdi, dirty_thresh, nr_dirty, bdi_dirty, current); if (unlikely(bw == 0)) { @@ -1241,6 +1251,8 @@ static void balance_dirty_pages(struct a pause = pause_max; goto pause; } + bw = min(bw, current->signal->rlim[RLIMIT_RSS].rlim_cur >> + PAGE_SHIFT); period = (HZ * pages_dirtied + bw / 2) / bw; pause = current->paused_when + period - jiffies; /* @@ -1292,8 +1304,8 @@ pause: current->paused_when += pause; current->nr_dirtied = 0; - if (nr_dirty < default_backing_dev_info.dirty_threshold + - default_backing_dev_info.dirty_threshold / DIRTY_MARGIN) + dirty_thresh = hard_dirty_limit(dirty_thresh); + if (nr_dirty < dirty_thresh + dirty_thresh / DIRTY_MARGIN) break; } -- 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/ . 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