On Mon, Oct 30, 2023 at 10:55:07AM -0700, Dave Hansen wrote: > On 10/30/23 00:25, Byungchul Park wrote: > > I'm suggesting a mechanism to reduce TLB flushes by keeping source and > > destination of folios participated in the migrations until all TLB > > flushes required are done, only if those folios are not mapped with > > write permission PTE entries at all. I worked Based on v6.6-rc5. > > There's a lot of common overhead here, on top of the complexity in general: > > * A new page flag > * A new cpumask_t in task_struct > * A new zone list > * Extra (temporary) memory consumption > > and the benefits are ... "performance improved a little bit" on one > workload. That doesn't seem like a good overall tradeoff to me. > > There will certainly be workloads that, before this patch, would have > little or no memory pressure and after this patch would need to do reclaim. 'if (gain - cost) > 0 ?'" is a difficult problem. I think the followings are already big benefit in general: 1. big reduction of IPIs # 2. big reduction of TLB flushes # 3. big reduction of TLB misses # Of course, I or we need to keep trying to see a better number in end-to-end performance. > Also, looking with my arch/x86 hat on, there's really nothing > arch-specific here. Please try to keep stuff out of arch/x86 unless > it's very much arch-specific. Okay. I will try to keep it out of arch code. I should give up an optimization that can be achieved by working on arch code tho. Byungchul
