On Mon, Mar 03, 2014 at 01:20:21PM +0100, Peter Lieven wrote: > On 03.03.2014 13:03, Stefan Hajnoczi wrote: > >So what is the actual performance problem you are trying to solve and > >what benchmark output are you getting when you compare with > >FADV_DONTNEED against without FADV_DONTNEED? > I found the performance to be identical. For the problem see below please. > > > >I think there's a danger that the discussion will go around in circles. > >Please post the performance results that kicked off this whole effort > >and let's focus on the data. That way it's much easier to evaluate what > >changes to QEMU are a win and which are not necessary. > I found that under memory pressure situations the increasing buffers > leads to vserver memory being swapped out. This caused trouble > especially in overcommit scenarios (where all memory is backed by > swap).
I think the general idea is qemu-img should not impact running guests, even on a heavily loaded machine. But again, this needs to be discussed using concrete benchmarks with configurations and results posted to the list. Stefan
