On Fri, May 17, 2024 at 03:48:49PM +0800, YangYang wrote: > On 2024/5/16 23:29, Benjamin Marzinski wrote: > > On Thu, May 16, 2024 at 09:55:53AM +0800, YangYang wrote: > > > On 2024/5/15 23:42, Benjamin Marzinski wrote: > > > > On Tue, May 14, 2024 at 05:04:42PM +0800, Yang Yang wrote: > > > > > > If I understand correctly, you are suggesting to iterate through all the > > > targets, handling those with sends_pass_around_flush set, and skipping > > > those where sends_pass_around_flush is not set. I believe this approach > > > may result in some CPU wastage. > > > > > > for i in {0..1023}; do > > > echo $((8000*$i)) 8000 linear /dev/sda2 $((16384*$i)) > > > done | sudo dmsetup create example > > > > > > In this specific scenario, a single iteration of the loop is all that > > > is needed. > > > > It's just one iteration of the loop either way. You either loop through > > the targets or the devices. It's true that if you have lots of targets > > all mapped to the same device, you would waste time looping through all > > the targets instead of looping through the devices. But if you only had > > one striped target mapped to lots of devices, you would waste time > > looping through all of the devices instead of looping through the > > targets. > > Yes, I get your point. This patchset may make things even worse for > the striped target. > I am just curious, in what scenario is the "dm-strip" target mapped to > a large number of underlying devices from the same block device. > I don't think anyone in the real world does create dm-stripe devices with a huge number of stripe table devices. My point was that it didn't seem obvious me that looping through the targets was a significant problem compared to looping through the devices. At any rate, Mikulas's patch already does this optimally, even for targets like dm-stripe, so it doesn't really matter now. -Ben