This series builds on top of the previous "mm: userspace hugepage collapse" series which introduced the MADV_COLLAPSE madvise mode and added support for private, anonymous mappings[1], by adding support for file and shmem backed memory to CONFIG_READ_ONLY_THP_FOR_FS=y kernels. File and shmem support have been added with effort to align with existing MADV_COLLAPSE semantics and policy decisions[2]. Collapse of shmem-backed memory ignores kernel-guiding directives and heuristics including all sysfs settings (transparent_hugepage/shmem_enabled), and tmpfs huge= mount options (shmem always supports large folios). Like anonymous mappings, on successful return of MADV_COLLAPSE on file/shmem memory, the contents of memory mapped by the addresses provided will be synchronously pmd-mapped THPs. This functionality unlocks two important uses: (1) Immediately back executable text by THPs. Current support provided by CONFIG_READ_ONLY_THP_FOR_FS may take a long time on a large system which might impair services from serving at their full rated load after (re)starting. Tricks like mremap(2)'ing text onto anonymous memory to immediately realize iTLB performance prevents page sharing and demand paging, both of which increase steady state memory footprint. Now, we can have the best of both worlds: Peak upfront performance and lower RAM footprints. (2) userfaultfd-based live migration of virtual machines satisfy UFFD faults by fetching native-sized pages over the network (to avoid latency of transferring an entire hugepage). However, after guest memory has been fully copied to the new host, MADV_COLLAPSE can be used to immediately increase guest performance. khugepaged has received a small improvement by association and can now detect and collapse pte-mapped THPs. However, there is still work to be done along the file collapse path. Compound pages of arbitrary order still needs to be supported and THP collapse needs to be converted to using folios in general. Eventually, we'd like to move away from the read-only and executable-mapped constraints currently imposed on eligible files and support any inode claiming huge folio support. That said, I think the series as-is covers enough to claim that MADV_COLLAPSE supports file/shmem memory. Patches 1-3 Implement the guts of the series. Patch 4 Is a tracepoint for debugging. Patches 5-8 Refactor existing khugepaged selftests to work with new memory types. Patch 9 Adds a userfaultfd selftest mode to mimic a functional test of UFFDIO_REGISTER_MODE_MINOR+MADV_COLLAPSE live migration. Applies against mm-unstable. [1] https://lore.kernel.org/linux-mm/20220706235936.2197195-1-zokeefe@xxxxxxxxxx/ [2] https://lore.kernel.org/linux-mm/YtBmhaiPHUTkJml8@xxxxxxxxxx/ Zach O'Keefe (9): mm/shmem: add flag to enforce shmem THP in hugepage_vma_check() mm/khugepaged: attempt to map file/shmem-backed pte-mapped THPs by pmds mm/madvise: add file and shmem support to MADV_COLLAPSE mm/khugepaged: add tracepoint to hpage_collapse_scan_file() selftests/vm: dedup THP helpers selftests/vm: modularize thp collapse memory operations selftests/vm: add thp collapse file and tmpfs testing selftests/vm: add thp collapse shmem testing selftests/vm: add selftest for MADV_COLLAPSE of uffd-minor memory include/linux/khugepaged.h | 11 +- include/linux/shmem_fs.h | 10 +- include/trace/events/huge_memory.h | 36 + kernel/events/uprobes.c | 2 +- mm/huge_memory.c | 2 +- mm/khugepaged.c | 285 ++++-- mm/shmem.c | 18 +- tools/testing/selftests/vm/Makefile | 2 + tools/testing/selftests/vm/khugepaged.c | 828 ++++++++++++------ tools/testing/selftests/vm/soft-dirty.c | 2 +- .../selftests/vm/split_huge_page_test.c | 12 +- tools/testing/selftests/vm/userfaultfd.c | 171 +++- tools/testing/selftests/vm/vm_util.c | 36 +- tools/testing/selftests/vm/vm_util.h | 5 +- 14 files changed, 1034 insertions(+), 386 deletions(-) -- 2.37.1.559.g78731f0fdb-goog
