On 25.11.20 09:38, Andrew Jones wrote: > On Tue, Nov 24, 2020 at 08:17:35PM +0100, David Hildenbrand wrote: >> On 24.11.20 19:11, Jonathan Cameron wrote: >>> On Mon, 9 Nov 2020 20:47:09 +0100 >>> David Hildenbrand <da...@redhat.com> wrote: >>> >>> +CC Eric based on similar query in other branch of the thread. >>> >>>> On 05.11.20 18:43, Jonathan Cameron wrote: >>>>> Basically a cut and paste job from the x86 support with the exception of >>>>> needing a larger block size as the Memory Block Size (MIN_SECTION_SIZE) >>>>> on ARM64 in Linux is 1G. >>>>> >>>>> Tested: >>>>> * In full emulation and with KVM on an arm64 server. >>>>> * cold and hotplug for the virtio-mem-pci device. >>>>> * Wide range of memory sizes, added at creation and later. >>>>> * Fairly basic memory usage of memory added. Seems to function as normal. >>>>> * NUMA setup with virtio-mem-pci devices on each node. >>>>> * Simple migration test. >>>>> >>>>> Related kernel patch just enables the Kconfig item for ARM64 as an >>>>> alternative to x86 in drivers/virtio/Kconfig >>>>> >>>>> The original patches from David Hildenbrand stated that he thought it >>>>> should >>>>> work for ARM64 but it wasn't enabled in the kernel [1] >>>>> It appears he was correct and everything 'just works'. >>>>> >>>>> The build system related stuff is intended to ensure virtio-mem support is >>>>> not built for arm32 (build will fail due no defined block size). >>>>> If there is a more elegant way to do this, please point me in the right >>>>> direction. >>>> >>>> You might be aware of https://virtio-mem.gitlab.io/developer-guide.html >>>> and the "issue" with 64k base pages - 512MB granularity. Similar as the >>>> question from Auger, have you tried running arm64 with differing page >>>> sizes in host/guest? >>>> >>> >>> Hi David, >>> >>>> With recent kernels, you can use "memhp_default_state=online_movable" on >>>> the kernel cmdline to make memory unplug more likely to succeed - >>>> especially with 64k base pages. You just have to be sure to not hotplug >>>> "too much memory" to a VM. >>> >>> Thanks for the pointer - that definitely simplifies testing. Was getting a >>> bit >>> tedious with out that. >>> >>> As ever other stuff got in the way, so I only just got back to looking at >>> this. >>> >>> I've not done a particularly comprehensive set of tests yet, but things seem >>> to 'work' with mixed page sizes. >>> >>> With 64K pages in general, you run into a problem with the device >>> block_size being >>> smaller than the subblock_size. I've just added a check for that into the >> >> "device block size smaller than subblock size" - that's very common, >> e.g., on x86-64. >> >> E.g., device_block_size is 2MiB, subblock size 4MiB - until we improve >> that in the future in Linux guests. >> >> Or did you mean something else? >> >>> virtio-mem kernel driver and have it fail to probe if that happens. I don't >>> think such a setup makes any sense anyway so no loss there. Should it make >>> sense >>> to drop that restriction in the future we can deal with that then without >>> breaking >>> backwards compatibility. >>> >>> So the question is whether it makes sense to bother with virtio-mem support >>> at all on ARM64 with 64k pages given currently the minimum workable >>> block_size >>> is 512MiB? I guess there is an argument of virtio-mem being a possibly more >>> convenient interface than full memory HP. Curious to hear what people >>> think on >>> this? >> >> IMHO we really want it. For example, RHEL is always 64k. This is a >> current guest limitation, to be improved in the future - either by >> moving away from 512MB huge pages with 64k or by improving >> alloc_contig_range(). > > Even with 64k pages you may be able to have 2MB huge pages by setting > default_hugepagesz=2M on the kernel command line.
Yes, but not for THP, right? Last time I checked that move was not performed yet - resulting in MAX_ORDER/pageblock_order in Linux corresponding to 512 MB. > > Thanks, > drew -- Thanks, David / dhildenb