> > > It creates a kthread to avoid the deadlock described in NBD > > > tools documentation. So, if nbd-client hangs waiting pages, the > > > kblockd thread can continue its work and free pages. > > > > Hmm, and if there are no other pages that can be freed? Unlikely, > > but can happen AFAICT. > > Correct. The patch improves the NBD behavior even if it is not > perfect. And I think if no other page can be freed your system is > in very bad move ;-)
Not necessarily. Problems start when the system wants to free memory by writing out pages through NBD, and the userspace process servicing it tries to allocate some memory in order to accomplish this. Recent kernels have gotten much better at coping with this, so it might not be easy to make local NBD deadlock under normal circumstances. But if you try hard enough, it's not impossible: throttle_vm_writeout() can stall an allocation until pending writes have completed, all with plenty of memory available in the system. BTW, you can basically substitute local NBD with fuse-over-loop, and get a similar kind of service, with similar problems. Miklos -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
