On Wed, Jul 30, 2014 at 05:39:14PM -0700, Paul E. McKenney wrote: > This series provides a prototype of an RCU-tasks implementation, which has > been requested to assist with tramopoline removal. This flavor of RCU > is task-based rather than CPU-based, and has voluntary context switch, > usermode execution, and the idle loops as its only quiescent states. > This selection of quiescent states ensures that at the end of a grace > period, there will no longer be any tasks depending on a trampoline that > was removed before the beginning of that grace period. This works because > such trampolines do not contain function calls, do not contain voluntary > context switches, do not switch to usermode, and do not switch to idle.
I'm concerned about the amount of system overhead this introduces. Polling for holdout tasks seems quite excessive. If I understand the intended use case correctly, the users of this will want to free relatively small amounts of memory; thus, waiting a while to do so seems fine, especially if the system isn't under any particular memory pressure. Thus, rather than polling, could you simply flag the holdout tasks, telling the scheduler "hey, next time you don't have anything better to do..."? Then don't bother with them again unless the system runs low on memory and asks you to free some. (And mandate that you can only use this to free memory rather than for any other purpose.) Also, ideally this should remain entirely optional; nothing in the core kernel should depend on it. - Josh Triplett -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
