Messages in this thread | | | Subject | Re: [PATCH-RFC] cfq: Disable low_latency by default for 2.6.32 | From | Mike Galbraith <> | Date | Thu, 26 Nov 2009 14:08:57 +0100 |
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On Thu, 2009-11-26 at 12:19 +0000, Mel Gorman wrote: > (cc'ing the people from the page allocator failure thread as this might be > relevant to some of their problems) > > I know this is very last minute but I believe we should consider disabling > the "low_latency" tunable for block devices by default for 2.6.32. There was > evidence that low_latency was a problem last week for page allocation failure > reports but the reproduction-case was unusual and involved high-order atomic > allocations in low-memory conditions. It took another few days to accurately > show the problem for more normal workloads and it's a bit more wide-spread > than just allocation failures. > > Basically, low_latency looks great as long as you have plenty of memory > but in low memory situations, it appears to cause problems that manifest > as reduced performance, desktop stalls and in some cases, page allocation > failures. I think most kernel developers are not seeing the problem as they > tend to test on beefier machines and without hitting swap or low-memory > situations for the most part. When they are hitting low-memory situations, > it tends to be for stress tests where stalls and low performance are expected.
Ouch. It was bad desktop stalls under heavy write that kicked the whole thing off.
-Mike
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