Re: [PATCH] mm: use global_dirty_limit in throttle_vm_writeout()

[Johannes Weiner]

On Fri, Mar 02, 2012 at 02:14:51PM +0800, Fengguang Wu wrote:
> 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>

Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx>
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