On Tuesday 23 March 2010, Oren Laadan wrote: > > Rafael J. Wysocki wrote: > > On Wednesday 17 March 2010, Oren Laadan wrote: > >> From: Matt Helsley <matthltc@xxxxxxxxxx> > >> > >> When the cgroup freezer is used to freeze tasks we do not want to thaw > >> those tasks during resume. Currently we test the cgroup freezer > >> state of the resuming tasks to see if the cgroup is FROZEN. If so > >> then we don't thaw the task. However, the FREEZING state also indicates > >> that the task should remain frozen. > >> > >> This also avoids a problem pointed out by Oren Ladaan: the freezer state > >> transition from FREEZING to FROZEN is updated lazily when userspace reads > >> or writes the freezer.state file in the cgroup filesystem. This means that > >> resume will thaw tasks in cgroups which should be in the FROZEN state if > >> there is no read/write of the freezer.state file to trigger this > >> transition before suspend. > >> > >> NOTE: Another "simple" solution would be to always update the cgroup > >> freezer state during resume. However it's a bad choice for several reasons: > >> Updating the cgroup freezer state is somewhat expensive because it requires > >> walking all the tasks in the cgroup and checking if they are each frozen. > >> Worse, this could easily make resume run in N^2 time where N is the number > >> of tasks in the cgroup. Finally, updating the freezer state from this code > >> path requires trickier locking because of the way locks must be ordered. > >> > >> Instead of updating the freezer state we rely on the fact that lazy > >> updates only manage the transition from FREEZING to FROZEN. We know that > >> a cgroup with the FREEZING state may actually be FROZEN so test for that > >> state too. This makes sense in the resume path even for partially-frozen > >> cgroups -- those that really are FREEZING but not FROZEN. > >> > >> Reported-by: Oren Ladaan <orenl@xxxxxxxxxxxxxxx> > >> Signed-off-by: Matt Helsley <matthltc@xxxxxxxxxx> > >> Cc: Cedric Le Goater <legoater@xxxxxxx> > >> Cc: Paul Menage <menage@xxxxxxxxxx> > >> Cc: Li Zefan <lizf@xxxxxxxxxxxxxx> > >> Cc: Rafael J. Wysocki <rjw@xxxxxxx> > >> Cc: Pavel Machek <pavel@xxxxxx> > >> Cc: linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx > > > > Looks reasonable. > > > > Is anyone handling that already or do you want me to take it to my tree? > > Yes, please do. Applied. Rafael -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>