> > > > As noted before, we defer flushing for vmalloc. We have a lazy-threshold > > which can be exposed(if you need it) over sysfs for tuning. So, we can add it. > > > > In a CPU isolation / NOHZ_FULL context, isolated CPUs will be running a > single userspace application that will never enter the kernel, unless > forced to by some interference (e.g. IPI sent from a housekeeping CPU). > > Increasing the lazy threshold would unfortunately only delay the > interference - housekeeping CPUs are free to run whatever, and so they will > eventually cause the lazy threshold to be hit and IPI all the CPUs, > including the isolated/NOHZ_FULL ones. > Do you have any testing results for your workload? I mean how much potentially we can allocate. Again, maybe it is just enough to back and once per-hour offload it. Apart of that how critical IPIing CPUs affect your workloads? > I was thinking maybe we could subdivide the vmap space into two regions > with their own thresholds, but a task may allocate/vmap stuff while on a HK > CPU and be moved to an isolated CPU afterwards, and also I still don't have > any strong guarantee about what accesses an isolated CPU can do in its > early entry code :( > I agree this is not worth to play with a vmap space in terms of splitting it. Sorry for later answer and thank you! -- Uladzislau Rezki
