On Fri, Feb 17, 2017 at 08:11:09PM +0900, Tetsuo Handa wrote: > On 2017/02/17 7:21, Dave Chinner wrote: > > FWIW, the major problem with removing the blocking in inode reclaim > > is the ease with which you can then trigger the OOM killer from > > userspace. The high level memory reclaim algorithms break down when > > there are hundreds of direct reclaim processes hammering on reclaim > > and reclaim stops making progress because it's skipping dirty > > objects. Direct reclaim ends up insufficiently throttled, so rather > > than blocking it winds up reclaim priority and then declares OOM > > because reclaim runs out of retries before sufficient memory has > > been freed. > > > > That, right now, looks to be an unsolvable problem without a major > > rework of direct reclaim. I've pretty much given up on ever getting > > the unbound direct reclaim concurrency problem that is causing us > > these problems fixed, so we are left to handle it in the subsystem > > shrinkers as best we can. That leaves us with an unfortunate choice: > > > > a) throttle excessive concurrency in the shrinker to prevent > > IO breakdown, thereby causing reclaim latency bubbles > > under load but having a stable, reliable system; or > > b) optimise for minimal reclaim latency and risk userspace > > memory demand triggering the OOM killer whenever there > > are lots of dirty inodes in the system. > > > > Quite frankly, there's only one choice we can make in this > > situation: reliability is always more important than performance. > > Is it possible to get rid of direct reclaim and let allocating thread > wait on queue? I wished such change in context of __GFP_KILLABLE at > http://lkml.kernel.org/r/201702012049.BAG95379.VJFFOHMStLQFOO@xxxxxxxxxxxxxxxxxxx . Yup, that's similar to what I've been suggesting - offloading the direct reclaim slowpath to a limited set of kswapd-like workers and blocking the allocating processes until there is either memory for them or OOM is declared... Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx -- To unsubscribe from this list: send the line "unsubscribe linux-xfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
