On Tue, Nov 28, 2023 at 4:28 PM Jason Gunthorpe <jgg@xxxxxxxx> wrote: > > On Tue, Nov 28, 2023 at 04:25:03PM -0800, Yosry Ahmed wrote: > > > > > Right, but as I mention above, if userspace starts depending on this > > > > equation, we won't be able to add any more classes of "secondary" page > > > > tables to SecPageTables. I'd like to avoid that if possible. We can do > > > > the subtraction in the kernel. > > > > > > What Sean had suggested was that SecPageTables was always intended to > > > account all the non-primary mmu memory used by page tables. If this is > > > the case we shouldn't be trying to break it apart into finer > > > counters. These are big picture counters, not detailed allocation by > > > owner counters. > > > > Right, I agree with that, but if SecPageTables includes page tables > > from multiple sources, and it is observed to be suspiciously high, the > > logical next step is to try to find the culprit, right? > > You can make that case already, if it is high wouldn't you want to > find the exact VMM process that was making it high? > > It is a sign of fire, not a detailed debug tool. Fair enough. We can always add separate counters later if needed, potentially under KVM stats to get more fine-grained details as you mentioned. I am only worried about users subtracting the iommu-only counter to get a KVM counter. We should at least document that SecPageTables may be expanded to include other sources later to avoid that. > > Jason
