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 . -- 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
