| Subject | Re: [PATCH 4/5] writeback: per task dirty rate limit | From | Peter Zijlstra <> | Date | Tue, 09 Aug 2011 20:35:06 +0200 |
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On Sat, 2011-08-06 at 16:44 +0800, Wu Fengguang wrote: > > Add two fields to task_struct. > > 1) account dirtied pages in the individual tasks, for accuracy > 2) per-task balance_dirty_pages() call intervals, for flexibility > > The balance_dirty_pages() call interval (ie. nr_dirtied_pause) will > scale near-sqrt to the safety gap between dirty pages and threshold. > > XXX: The main problem of per-task nr_dirtied is, if 10k tasks start > dirtying pages at exactly the same time, each task will be assigned a > large initial nr_dirtied_pause, so that the dirty threshold will be > exceeded long before each task reached its nr_dirtied_pause and hence > call balance_dirty_pages().
Right, so why remove the per-cpu threshold? you can keep that as a bound on the number of out-standing dirty pages.
Loosing that bound is actually a bad thing (TM), since you could have configured a tight dirty limit and lock up your machine this way.
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