Andrea Arcangeli <aarcange@xxxxxxxxxx> writes: > On Mon, Jan 23, 2012 at 05:18:57PM +0100, Jan Kara wrote: >> requst granularity. Sure, big requests will take longer to complete but >> maximum request size is relatively low (512k by default) so writing maximum >> sized request isn't that much slower than writing 4k. So it works OK in >> practice. > > Totally unrelated to the writeback, but the merged big 512k requests > actually adds up some measurable I/O scheduler latencies and they in > turn slightly diminish the fairness that cfq could provide with > smaller max request size. Probably even more measurable with SSDs (but > then SSDs are even faster). Are you speaking from experience? If so, what workloads were negatively affected by merging, and how did you measure that? Cheers, Jeff -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
