Hello Jeff, On Wed, Mar 24, 2021 at 11:07 PM Jeff Moyer <jmoyer@xxxxxxxxxx> wrote: > > Hi, Ming, > > Ming Lei <tom.leiming@xxxxxxxxx> writes: > > > Hello Guys, > > > > It is observed that nr_cpu * mlock(128M) is called when exiting > > 'blktrace -b 8192 -d $DEV'. And OOM is easily triggered when the > > machine has lots of CPU cores. > > The only mlock in the code appears to happen at setup time. How did you > determine this was occurring in the exit path? It is triggered when pressing 'ctrl^ + C' on 'blktrace -b 8192 -d /dev/nullb0', at that time blktrace needs to parse collected trace, even though there is nothing collected on nullb0. > > > So can we figure out one way to not lock big buffer for avoiding > > OOM? > > The obvious question is why are you using -b 8192? Were you losing > events without that option? It is used by device-mapper[1] which is covered in Red Hat kernel CKI. Seems the locked buffer size is 16 * (buffer size) which is specified by '-b'. So at default per-cpu mlock(16 * 512K) will be done, when nr_cpu is bigger, it still risks in OOM. [1] https://github.com/jthornber/device-mapper-test-suite.git Thanks, Ming Lei
