This patch set (against nfsd-next) enables automatic adjustment of the number of nfsd threads. The number can increase under high load, and reduce after idle periods. The first few patches (1-6) are cleanups that may not be entirely relevant to the current series. They could safely land any time and only need minimal review. Patch 9,10,11 remove some places were sv_nrthreads are used for things other than counting threads. It is use to adjust other limits. At the time this seemed like an easy and sensible solution. I now have to repent of that short-cut and find a better way to impose reasonable limits. These and the other sundry patches (7,8,12) can, I think safely land whenever that get sufficient review. I think they are sensible even if we won't end up adjusting threads dynamically. Patches 13 and 14 build on all this to provide the desired functionality. Patch 13 allows the maximum to be configured, and patch 14 starts or stops threads based on some simple triggers. For 13 I decided that if the user/admin makes no explicit configuration, then the currently request number of threads becomes a minimum, and a maximum is determined based on the amount of memory. This will make the patch set immediately useful but shouldn't unduly impact existing configurations. For patch 14 I only implemented starting a thread when there is work to do but no threads to do it, and stopping a thread when it has been idle for 5 seconds. The start-up is deliberately serialised so at least one NFS request is serviced between the decision to start a thread and the action of starting it. This hopefully encourages a ramping up of thread count rather than a sudden jump. There is certain room for discussion around the wisdom of these heuristics, and what other heuristics are needed - we probably want a shrinker to impose memory pressure of the number of threads. We probably want a thread to exit rather than retry when a memory allocation in svc_alloc_arg() fails. I certainly wouldn't recommend patch 14 landing in any hurry at all. I'd love to hear what y'all think, and what experiences you have when testing it. Thanks, NeilBrown
