> Il giorno 19 feb 2018, alle ore 06:34, Mike Galbraith <efault@xxxxxx> ha scritto: > > FWIW, my box spent the weekend running a kbuild marathon with a52a69ea > reverted, has convinced me that it _is_ the source of the hang woes > (directly or indirectly). No outright stalls, no stall for way too > long but then recover, nada, not the slightest hint of trouble. > ok, after this piece of evidence, and while waiting for more authoritative suggestions, I have investigated a little bit how to reduce the number of your angry tags available, to hopefully push your system so close to failure to have your problem reproduced reliably and quickly. The only easy way seems to be that you, as root, issue an echo 4 > /sys/block/sda/queue/nr_requests (nr_requests is lower-bounded to 4) NOTE: do/repeat this *after* you switch to a new scheduler, because a scheduler switch restores a high 62 value. Reducing nr_requests does not change the value of the nr_tags parameter, but, according to the code, it should de facto reduce the number of available tags, by reducing the depth of the bitmaps of free tags. Thanks, Paolo > -Mike