On 20 August 2017 at 01:34, Mikulas Patocka <mpatocka@xxxxxxxxxx> wrote: > > If you issue a single ioctl that takes extreme amount of time - the kernel > warns about being blocked for extreme amount of time - what else should it > do? > But as I said, it does NOT warn about being blocked if the ioctl is issued for a SCSI device (i.e. blkdiscard -z /dev/sdX), so why the warning occurs / cannot be avoided in the case of a dm(-crypt) container? One thing I can see is, when blkdiscard -z is running on a dm-crypt container, iostat list it with a big avgqu-sz (not to be mixed up with avgrq-sz), starting from ~40000 (the underlying device is a 37G partition), gradually dropping to 0 (when the job is finished) with a step of ~40; all other items are 0 for the container (except %util, also 100% for most of the time). While for the underlying device, no matter if it is written to through a dm-crypt container, its lines stays at something like these: Device: rrqm/s wrqm/s r/s w/s rkB/s wkB/s avgrq-sz avgqu-sz await r_await w_await svctm %util sdb 0.00 0.00 0.00 85.00 0.00 43520.00 1024.00 144.71 1664.89 0.00 1664.89 11.76 100.00 sdb 0.00 0.00 0.00 86.00 0.00 44032.00 1024.00 142.34 1694.70 0.00 1694.70 11.63 100.00 -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
