* Mel Gorman <mgorman@xxxxxxx> wrote: > > I think since it is you who wants to introduce additional complexity into the > > x86 MM code the burden is on you to provide proof that the complexity of pfn > > (or struct page) tracking is worth it. > > I'm taking a situation whereby IPIs are sent like crazy with interrupt storms > and replacing it with something that is a lot more efficient that minimises the > number of potential surprises. I'm stating that the benefit of PFN tracking is > unknowable in the general case because it depends on the workload, timing and > the exact CPU used so any example provided can be naked with a counter-example > such as a trivial sequential reader that shows no benefit. The series as posted > is approximately in line with current behaviour minimising the chances of > surprise regressions from excessive TLB flush. > > You are actively blocking a measurable improvement and forcing it to be replaced > with something whose full impact is unquantifiable. Any regressions in this area > due to increased TLB misses could take several kernel releases as the issue will > be so difficult to detect. > > I'm going to implement the approach you are forcing because there is an x86 part > of the patch and you are the maintainer that could indefinitely NAK it. However, > I'm extremely pissed about being forced to introduce these indirect > unpredictable costs because I know the alternative is you dragging this out for > weeks with no satisfactory conclusion in an argument that I cannot prove in the > general case. Stop this crap. I made a really clear and unambiguous chain of arguments: - I'm unconvinced about the benefits of INVLPG in general, and your patches adds a whole new bunch of them. I cited measurements and went out on a limb to explain my position, backed with numbers and logic. It's admittedly still a speculative position and I might be wrong, but I think it's well grounded position that you cannot just brush aside. - I suggested that you split this approach into steps that first does the simpler approach that will give us at least 95% of the benefits, then the more complex one on top of it. Your false claim that I'm blocking a clear improvement is pure demagogy! - I very clearly claimed that I am more than willing to be convinced by numbers. It's not _that_ hard to construct a memory trashing workload with a TLB-efficient iteration that uses say 80% of the TLB cache, to measure the worst-case overhead of full flushes. I'm really sick of this partly deceptive, partly passive-aggressive discussion style that seems to frequently permeate VM discussions and which made sched/numa such a huge PITA in the past... And I think the numbers in the v6 series you submitted today support my position, so you owe me an apology I think ... Thanks, Ingo -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>