On Mon, Sep 20, 2021 at 04:11:52PM +0200, David Sterba wrote: > On Mon, Sep 20, 2021 at 01:50:58PM +0100, Mel Gorman wrote: > > On Mon, Sep 20, 2021 at 12:42:44PM +0100, Matthew Wilcox wrote: > > > On Mon, Sep 20, 2021 at 09:54:31AM +0100, Mel Gorman wrote: > > > > This has been lightly tested only and the testing was useless as the > > > > relevant code was not executed. The workload configurations I had that > > > > used to trigger these corner cases no longer work (yey?) and I'll need > > > > to implement a new synthetic workload. If someone is aware of a realistic > > > > workload that forces reclaim activity to the point where reclaim stalls > > > > then kindly share the details. > > > > > > The stereeotypical "stalling on I/O" problem is to plug in one of the > > > crap USB drives you were given at a trade show and simply > > > dd if=/dev/zero of=/dev/sdb > > > sync > > > > > > > The test machines are 1500KM away so plugging in a USB stick but worst > > comes to the worst, I could test it on a laptop. > > There's a device mapper target dm-delay [1] that as it says delays the > reads and writes, so you could try to emulate the slow USB that way. > > [1] https://www.kernel.org/doc/html/latest/admin-guide/device-mapper/delay.html Ah, thanks for that tip. I wondered if something like this existed and clearly did not search hard enough. I was able to reproduce the problem without throttling but this could still be useful if examining cases where there are 2 or more BDIs with variable speeds. -- Mel Gorman SUSE Labs
