Messages in this thread | | | From | Neil Brown <> | Date | Thu, 17 Aug 2006 14:08:58 +1000 | Subject | Re: RFC - how to balance Dirty+Writeback in the face of slow writeback. |
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On Wednesday August 16, dgc@sgi.com wrote: > > IMO, if you've got slow writeback, you should be reducing the amount > of dirty memory you allow in the machine so that you don't tie up > large amounts of memory that takes a long time to clean. Throttle earlier > and you avoid this problem entirely.
I completely agree that 'throttle earlier' is important. I just not completely sure what should be throttled when.
I think I could argue that pages in 'Writeback' are really still dirty. The difference is really just an implementation issue.
So when the dirty_ratio is set to 40%, that should apply to all 'dirty' pages, which means both that flagged as 'Dirty' and those flagged as 'Writeback'.
So I think you need to throttle when Dirty+Writeback hits dirty_ratio (which we don't quite get right at the moment). But the trick is to throttle gently and fairly, rather than having a hard wall so that any one who hits it just stops.
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