Base ====
This series is based on top of my series which adds minor fault handling for hugetlbfs [1]. (And, therefore, it is based on 5.12-rc1 and Peter Xu's series for disabling huge pmd sharing as well.)
[1] https://lore.kernel.org/linux-fsdevel/20210301222728.176417-1-axelrasmussen@...
Changelog =========
v1->v2: - For UFFDIO_CONTINUE, don't mess with page flags. Just use find_lock_page to get a locked page from the page cache, instead of doing __SetPageLocked. This fixes a VM_BUG_ON v1 hit when handling minor faults for THP-backed shmem (a tmpfs mounted with huge=always).
Overview ========
See my original series linked above for a detailed overview of minor fault handling in general. The feature in this series works exactly like the hugetblfs version (from userspace's perspective).
I'm sending this as a separate series because:
- The original minor fault handling series has a full set of R-Bs, and seems close to being merged. So, it seems reasonable to start looking at this next step, which extends the basic functionality.
- shmem is different enough that this series may require some additional work before it's ready, and I don't want to delay the original series unnecessarily by bundling them together.
Use Case ========
In some cases it is useful to have VM memory backed by tmpfs instead of hugetlbfs. So, this feature will be used to support the same VM live migration use case described in my original series.
Additionally, Android folks (Lokesh Gidra lokeshgidra@google.com) hope to optimize the Android Runtime garbage collector using this feature:
"The plan is to use userfaultfd for concurrently compacting the heap. With this feature, the heap can be shared-mapped at another location where the GC-thread(s) could continue the compaction operation without the need to invoke userfault ioctl(UFFDIO_COPY) each time. OTOH, if and when Java threads get faults on the heap, UFFDIO_CONTINUE can be used to resume execution. Furthermore, this feature enables updating references in the 'non-moving' portion of the heap efficiently. Without this feature, uneccessary page copying (ioctl(UFFDIO_COPY)) would be required."
Axel Rasmussen (5): userfaultfd: support minor fault handling for shmem userfaultfd/selftests: use memfd_create for shmem test type userfaultfd/selftests: create alias mappings in the shmem test userfaultfd/selftests: reinitialize test context in each test userfaultfd/selftests: exercise minor fault handling shmem support
fs/userfaultfd.c | 6 +- include/linux/shmem_fs.h | 26 +- include/uapi/linux/userfaultfd.h | 4 +- mm/memory.c | 8 +- mm/shmem.c | 92 +++---- mm/userfaultfd.c | 27 +- tools/testing/selftests/vm/userfaultfd.c | 322 +++++++++++++++-------- 7 files changed, 295 insertions(+), 190 deletions(-)
-- 2.30.1.766.gb4fecdf3b7-goog