Messages in this thread | | | Date | Fri, 11 Jun 2010 14:33:37 -0700 | From | Andrew Morton <> | Subject | Re: [PATCH 5/6] vmscan: Write out ranges of pages contiguous to the inode where possible |
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On Fri, 11 Jun 2010 21:44:11 +0100 Mel Gorman <mel@csn.ul.ie> wrote:
> > Well. The main problem is that we're doing too much IO off the LRU of > > course. > > > > What would be considered "too much IO"?
Enough to slow things down ;)
This problem used to hurt a lot. Since those times we've decreased the default value of /proc/sys/vm/dirty*ratio by a lot, which surely papered over this problem a lot. We shouldn't forget that those ratios _are_ tunable, after all. If we make a change which explodes the kernel when someone's tuned to 40% then that's a problem and we'll need to scratch our heads over the magnitude of that problem.
As for a workload which triggers the problem on a large machine which is tuned to 20%/10%: dunno. If we're reliably activating pages when dirtying them then perhaps it's no longer a problem with the default tuning. I'd do some testing with mem=256M though - that has a habit of triggering weirdnesses.
btw, I'm trying to work out if zap_pte_range() really needs to run set_page_dirty(). Didn't (pte_dirty() && !PageDirty()) pages get themselves stamped out?
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