[$] A pair of workqueue improvements

Over the years, the kernel has developed a number of deferred-executionmechanisms to take care of work that cannot be done immediately. For many(or most) needs, the workqueuesubsystem is the tool that developers reach for first. Workqueuestook their current form over a dozen yearsago, but that does not mean that there are not improvements to be made.Two sets of patches from Tejun Heo show the pressures being felt by theworkqueue subsystem and the solutions that are being tried - with varyingdegrees of success.