On Thu, Apr 15, 2010 at 03:35:14PM +0900, KOSAKI Motohiro wrote: > > On Thu, Apr 15, 2010 at 01:09:01PM +0900, KOSAKI Motohiro wrote: > > > Hi > > > > > > > How about this? For now, we stop direct reclaim from doing writeback > > > > only on order zero allocations, but allow it for higher order > > > > allocations. That will prevent the majority of situations where > > > > direct reclaim blows the stack and interferes with background > > > > writeout, but won't cause lumpy reclaim to change behaviour. > > > > This reduces the scope of impact and hence testing and validation > > > > the needs to be done. > > > > > > Tend to agree. but I would proposed slightly different algorithm for > > > avoind incorrect oom. > > > > > > for high order allocation > > > allow to use lumpy reclaim and pageout() for both kswapd and direct reclaim > > > > SO same as current. > > Yes. as same as you propsed. > > > > > > for low order allocation > > > - kswapd: always delegate io to flusher thread > > > - direct reclaim: delegate io to flusher thread only if vm pressure is low > > > > IMO, this really doesn't fix either of the problems - the bad IO > > patterns nor the stack usage. All it will take is a bit more memory > > pressure to trigger stack and IO problems, and the user reporting the > > problems is generating an awful lot of memory pressure... > > This patch doesn't care stack usage. because > - again, I think all stack eater shold be diet. Agreed (again), but we've already come to the conclusion that a stack diet is not enough. > - under allowing lumpy reclaim world, only deny low order reclaim > doesn't solve anything. Yes, I suggested it *as a first step*, not as the end goal. Your patches don't reach the first step which is fixing the reported stack problem for order-0 allocations... > Please don't forget priority=0 recliam failure incvoke OOM-killer. > I don't imagine anyone want it. Given that I haven't been able to trigger OOM without writeback from direct reclaim so far (*) I'm not finding any evidence that it is a problem or that there are regressions. I want to be able to say that this change has no known regressions. I want to find the regression and work to fix them, but without test cases there's no way I can do this. This is what I'm getting frustrated about - I want to fix this problem once and for all, but I can't find out what I need to do to robustly test such a change so we can have a high degree of confidence that it doesn't introduce major regressions. Can anyone help here? (*) except in one case I've already described where it mananged to allocate enough huge pages to starve the system of order zero pages, which is what I asked it to do. > And, Which IO workload trigger <6 priority vmscan? You're asking me? I've been asking you for workloads that wind up reclaim priority.... :/ All I can say is that the most common trigger I see for OOM is copying a large file on a busy system that is running off a single spindle. When that happens on my laptop I walk away and get a cup of coffee when that happens and when I come back I pick up all the broken bits the OOM killer left behind..... Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
