On Tue, Feb 13, 2024 at 10:44:53AM -0500, Pasha Tatashin wrote: > > > SecPageTables > > > - Memory consumed by secondary page tables, this currently > > > - currently includes KVM mmu allocations on x86 and arm64. > > > + Memory consumed by secondary page tables, this currently includes > > > + KVM mmu and IOMMU allocations on x86 and arm64. > > Hi Will, > > > While I can see the value in this for IOMMU mappings managed by VFIO, > > doesn't this end up conflating that with the normal case of DMA domains? > > For systems that e.g. rely on an IOMMU for functional host DMA, it seems > > wrong to subject that to accounting constraints. > > The accounting constraints are only applicable when GFP_KERNEL_ACCOUNT > is passed to the iommu mapping functions. We do that from the vfio, > iommufd, and vhost. Without this flag, the memory useage is reported > in /proc/meminfo as part of SecPageTables field, but not constrained > in cgroup. Thanks, Pasha, that explanation makes sense. I still find it bizarre to include IOMMU allocations from the DMA API in SecPageTables though, and I worry that it will confuse people who are using that metric as a way to get a feeling for how much memory is being used by KVM's secondary page-tables. As an extreme example, having a non-zero SecPageTables count without KVM even compiled in is pretty bizarre. Will
