On Thu, Jul 21, 2011 at 05:28:42PM +0100, Mel Gorman wrote:
> Warning: Long post with lots of figures. If you normally drink coffee
> and you don't have a cup, get one or you may end up with a case of
> keyboard face.
> Overall, having kswapd avoiding writes does improve performance
> which is not a surprise. Dave asked "do we even need IO at all from
> reclaim?". On NUMA machines, the answer is "yes" unless the VM can
> wake the flusher thread to clean a specific node.
Great answer, Mel. ;)
> When kswapd never
> writes, processes can stall for significant periods of time waiting on
> flushers to clean the correct pages. If all writing is to be deferred
> to flushers, it must ensure that many writes on one node would not
> starve requests for cleaning pages on another node.
Ok, so that's a direction we need to work towards, then.
> I'm currently of the opinion that we should consider merging patches
> 1-7 and discuss what is required before merging. It can be tackled
> later how the flushers can prioritise writing of pages belonging to
> a particular zone before disabling all writes from reclaim.
Sounds reasonable to me.