When starting a memory hog task, a desktop box w/o swap is found to go
unresponsive for a long time. It's solely caused by lots of congestion
waits in throttle_vm_writeout():
gnome-system-mo-4201 553.073384: congestion_wait: throttle_vm_writeout+0x70/0x7f shrink_mem_cgroup_zone+0x48f/0x4a1
gnome-system-mo-4201 553.073386: writeback_congestion_wait: usec_timeout=100000 usec_delayed=100000
gtali-4237 553.080377: congestion_wait: throttle_vm_writeout+0x70/0x7f shrink_mem_cgroup_zone+0x48f/0x4a1
gtali-4237 553.080378: writeback_congestion_wait: usec_timeout=100000 usec_delayed=100000
Xorg-3483 553.103375: congestion_wait: throttle_vm_writeout+0x70/0x7f shrink_mem_cgroup_zone+0x48f/0x4a1
Xorg-3483 553.103377: writeback_congestion_wait: usec_timeout=100000 usec_delayed=100000
The root cause is, the dirty threshold is knocked down a lot by the
memory hog task. Fixed by using global_dirty_limit which decreases
gradually on such events and can guarantee we stay above (the also
decreasing) nr_dirty in the progress of following down to the new
dirty threshold.
Signed-off-by: Fengguang Wu <fengguang.wu@xxxxxxxxx>
---
mm/page-writeback.c | 1 +
1 file changed, 1 insertion(+)
--- linux.orig/mm/page-writeback.c 2012-03-02 14:05:01.633763187 +0800
+++ linux/mm/page-writeback.c 2012-03-02 14:11:52.929772962 +0800
@@ -1472,6 +1472,7 @@ void throttle_vm_writeout(gfp_t gfp_mask
for ( ; ; ) {
global_dirty_limits(&background_thresh, &dirty_thresh);
+ dirty_thresh = hard_dirty_limit(dirty_thresh);
/*
* Boost the allowable dirty threshold a bit for page
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@xxxxxxxxx. For more info on Linux MM,
see: http://www.linux-mm.org/ .
Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/
Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>