On Tue, Apr 26, 2022 at 12:27:57PM -0700, Yosry Ahmed wrote: > > What page tables do we want to account? KVM on ARM manages several page > > tables. > > > > For regular KVM, the host kernel manages allocations for the hyp stage 1 > > tables in addition to the stage 2 tables used for a particular VM. The > > former is system overhead whereas the latter could be attributed to a > > guest VM. > > Honestly I would love to get your input on this. The main motivation > here is to give users insights on the kernel memory usage on their > system (or in a cgroup). We currently have NR_PAGETABLE stats for > normal kernel page tables (allocated using > __pte_alloc_one()/pte_free()), this shows up in /proc/meminfo, > /path/to/cgroup/memory.stat, and node stats. The idea is to add > NR_SECONDARY_PAGETABLE that should include the memory used for kvm > pagetables, which should be a separate category (no overlap). What > gets included or not depends on the semantics of KVM and what exactly > falls under the category of secondary pagetables from the user's pov. > > Currently it looks like s2 page table allocations get accounted to > kmem of memory control groups (GFP_KERNEL_ACCOUNT), while hyp page > table allocations do not (GFP_KERNEL). So we could either follow this > and only account s2 page table allocations in the stats, or make hyp > allocations use GFP_KERNEL_ACCOUNT as well and add them to the stats. > Let me know what you think. I think it is reasonable to just focus on stage 2 table allocations and ignore all else. As Marc pointed out it isn't workable in other contexts anyway (pKVM), and keeps the patch tidy too. GFP_KERNEL_ACCOUNT for hyp allocations wouldn't make sense, as it is done at init to build out the system page tables for EL2. -- Thanks, Oliver
