| Message ID | 20210519200339.829146-1-axelrasmussen@google.com (mailing list archive) |
|---|---|
| Headers | show |
| Series | KVM: selftests: exercise userfaultfd minor faults | expand |
On 19/05/21 22:03, Axel Rasmussen wrote: > Base > ==== > > These patches are based upon Andrew Morton's v5.13-rc1-mmots-2021-05-13-17-23 > tag. This is because this series depends on: > > - UFFD minor fault support for hugetlbfs (in v5.13-rc1) [1] > - UFFD minor fault support for shmem (in Andrew's tree) [2] > > [1] https://lore.kernel.org/linux-fsdevel/20210301222728.176417-1-axelrasmussen@google.com/ > [2] https://lore.kernel.org/patchwork/cover/1420967/ > > Changelog > ========= > > v1->v2: > - Picked up Reviewed-by's. > - Change backing_src_is_shared() to check the flags, instead of the type. This > makes it robust to adding new backing source types in the future. > - Add another commit which refactors setup_demand_paging() error handling. > - Print UFFD ioctl type once in setup_demand_paging, instead of on every page-in > operation. > - Expand comment on why we use MFD_HUGETLB instead of MAP_HUGETLB. > - Reworded comment on addr_gpa2alias. > - Moved demand_paging_test.c timing calls outside of the if (), deduplicating > them. > - Split trivial comment / logging fixups into a separate commit. > - Add another commit which prints a clarifying message on test skip. > - Split the commit allowing backing src_type to be modified in two. > - Split the commit adding the shmem backing type in two. > - Rebased onto v5.13-rc1-mmots-2021-05-13-17-23. > > Overview > ======== > > Minor fault handling is a new userfaultfd feature whose goal is generally to > improve performance. In particular, it is intended for use with demand paging. > There are more details in the cover letters for this new feature (linked above), > but at a high level the idea is that we think of these three phases of live > migration of a VM: > > 1. Precopy, where we copy "some" pages from the source to the target, while the > VM is still running on the source machine. > 2. Blackout, where execution stops on the source, and begins on the target. > 3. Postcopy, where the VM is running on the target, some pages are already up > to date, and others are not (because they weren't copied, or were modified > after being copied). > > During postcopy, the first time the guest touches memory, we intercept a minor > fault. Userspace checks whether or not the page is already up to date. If > needed, we copy the final version of the page from the soure machine. This > could be done with RDMA for example, to do it truly in place / with no copying. > At this point, all that's left is to setup PTEs for the guest: so we issue > UFFDIO_CONTINUE. No copying or page allocation needed. > > Because of this use case, it's useful to exercise this as part of the demand > paging test. It lets us ensure the use case works correctly end-to-end, and also > gives us an in-tree way to profile the end-to-end flow for future performance > improvements. > > Axel Rasmussen (10): > KVM: selftests: trivial comment/logging fixes > KVM: selftests: simplify setup_demand_paging error handling > KVM: selftests: print a message when skipping KVM tests > KVM: selftests: compute correct demand paging size > KVM: selftests: allow different backing source types > KVM: selftests: refactor vm_mem_backing_src_type flags > KVM: selftests: add shmem backing source type > KVM: selftests: create alias mappings when using shared memory > KVM: selftests: allow using UFFD minor faults for demand paging > KVM: selftests: add shared hugetlbfs backing source type > > .../selftests/kvm/demand_paging_test.c | 175 +++++++++++------- > .../testing/selftests/kvm/include/kvm_util.h | 1 + > .../testing/selftests/kvm/include/test_util.h | 12 ++ > tools/testing/selftests/kvm/lib/kvm_util.c | 84 ++++++++- > .../selftests/kvm/lib/kvm_util_internal.h | 2 + > tools/testing/selftests/kvm/lib/test_util.c | 51 +++-- > 6 files changed, 238 insertions(+), 87 deletions(-) > > -- > 2.31.1.751.gd2f1c929bd-goog > Queued, thanks (with region->fd moved to the right patch). Paolo