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Fri, 27 Oct 2023 17:38:23 -0700 (PDT) Date: Fri, 27 Oct 2023 17:38:10 -0700 Mime-Version: 1.0 X-Mailer: git-send-email 2.42.0.820.g83a721a137-goog Message-ID: <20231028003819.652322-1-surenb@google.com> Subject: [PATCH v4 0/5] userfaultfd move option From: Suren Baghdasaryan To: akpm@linux-foundation.org Cc: viro@zeniv.linux.org.uk, brauner@kernel.org, shuah@kernel.org, aarcange@redhat.com, lokeshgidra@google.com, peterx@redhat.com, david@redhat.com, hughd@google.com, mhocko@suse.com, axelrasmussen@google.com, rppt@kernel.org, willy@infradead.org, Liam.Howlett@oracle.com, jannh@google.com, zhangpeng362@huawei.com, bgeffon@google.com, kaleshsingh@google.com, ngeoffray@google.com, jdduke@google.com, surenb@google.com, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, kernel-team@android.com X-Rspamd-Queue-Id: 0AEBB18000B X-Rspam-User: X-Rspamd-Server: rspam05 X-Stat-Signature: oxno9gonhszbg886e876gyibge4wkh15 X-HE-Tag: 1698453503-670967 X-HE-Meta: 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 wrRGTF13 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: This patch series introduces UFFDIO_MOVE feature to userfaultfd, which has long been implemented and maintained by Andrea in his local tree [1], but was not upstreamed due to lack of use cases where this approach would be better than allocating a new page and copying the contents. Previous upstraming attempts could be found at [6] and [7]. UFFDIO_COPY performs ~20% better than UFFDIO_MOVE when the application needs pages to be allocated [2]. However, with UFFDIO_MOVE, if pages are available (in userspace) for recycling, as is usually the case in heap compaction algorithms, then we can avoid the page allocation and memcpy (done by UFFDIO_COPY). Also, since the pages are recycled in the userspace, we avoid the need to release (via madvise) the pages back to the kernel [3]. We see over 40% reduction (on a Google pixel 6 device) in the compacting thread’s completion time by using UFFDIO_MOVE vs. UFFDIO_COPY. This was measured using a benchmark that emulates a heap compaction implementation using userfaultfd (to allow concurrent accesses by application threads). More details of the usecase are explained in [3]. Furthermore, UFFDIO_MOVE enables moving swapped-out pages without touching them within the same vma. Today, it can only be done by mremap, however it forces splitting the vma. TODOs for follow-up improvements: - cross-mm support. Known differences from single-mm and missing pieces: - memcg recharging (might need to isolate pages in the process) - mm counters - cross-mm deposit table moves - cross-mm test - document the address space where src and dest reside in struct uffdio_move - TLB flush batching. Will require extensive changes to PTL locking in move_pages_pte(). OTOH that might let us reuse parts of mremap code. Changes since v3 [8]: - changed retry path in folio_lock_anon_vma_read() to unlock and then relock RCU, per Peter Xu - removed cross-mm support from initial patchset, per David Hildenbrand - replaced BUG_ONs with VM_WARN_ON or WARN_ON_ONCE, per David Hildenbrand - added missing cache flushing, per Lokesh Gidra and Peter Xu - updated manpage text in the patch description, per Peter Xu - renamed internal functions from "remap" to "move", per Peter Xu - added mmap_changing check after taking mmap_lock, per Peter Xu - changed uffd context check to ensure dst_mm is registered onto uffd we are operating on, Peter Xu and David Hildenbrand - changed to non-maybe variants of maybe*_mkwrite(), per David Hildenbrand - fixed warning for CONFIG_TRANSPARENT_HUGEPAGE=n, per kernel test robot - comments cleanup, per David Hildenbrand and Peter Xu - checks for VM_IO,VM_PFNMAP,VM_HUGETLB,..., per David Hildenbrand - prevent moving pinned pages, per Peter Xu - changed uffd tests to call move uffd_test_ctx_clear() at the end of the test run instead of in the beginning of the next run - added support for testcase-specific ops - added test for moving PMD-aligned blocks Changes since v2 [5]: - renamed UFFDIO_REMAP to UFFDIO_MOVE, per David Hildenbrand - rebase over mm-unstable to use folio_move_anon_rmap(), per David Hildenbrand - added text for manpage explaining DONTFORK and KSM requirements for this feature, per David Hildenbrand - check for anon_vma changes in the fast path of folio_lock_anon_vma_read, per Peter Xu - updated the title and description of the first patch, per David Hildenbrand - updating comments in folio_lock_anon_vma_read() explaining the need for anon_vma checks, per David Hildenbrand - changed all mapcount checks to PageAnonExclusive, per Jann Horn and David Hildenbrand - changed counters in remap_swap_pte() from MM_ANONPAGES to MM_SWAPENTS, per Jann Horn - added a check for PTE change after folio is locked in remap_pages_pte(), per Jann Horn - added handling of PMD migration entries and bailout when pmd_devmap(), per Jann Horn - added checks to ensure both src and dst VMAs are writable, per Peter Xu - added UFFD_FEATURE_MOVE, per Peter Xu - removed obsolete comments, per Peter Xu - renamed remap_anon_pte to remap_present_pte, per Peter Xu - added a comment for folio_get_anon_vma() explaining the need for anon_vma checks, per Peter Xu - changed error handling in remap_pages() to make it more clear, per Peter Xu - changed EFAULT to EAGAIN to retry when a hugepage appears or disappears from under us, per Peter Xu - added links to previous upstreaming attempts, per David Hildenbrand Changes since v1 [4]: - add mmget_not_zero in userfaultfd_remap, per Jann Horn - removed extern from function definitions, per Matthew Wilcox - converted to folios in remap_pages_huge_pmd, per Matthew Wilcox - use PageAnonExclusive in remap_pages_huge_pmd, per David Hildenbrand - handle pgtable transfers between MMs, per Jann Horn - ignore concurrent A/D pte bit changes, per Jann Horn - split functions into smaller units, per David Hildenbrand - test for folio_test_large in remap_anon_pte, per Matthew Wilcox - use pte_swp_exclusive for swapcount check, per David Hildenbrand - eliminated use of mmu_notifier_invalidate_range_start_nonblock, per Jann Horn - simplified THP alignment checks, per Jann Horn - refactored the loop inside remap_pages, per Jann Horn - additional clarifying comments, per Jann Horn Main changes since Andrea's last version [1]: - Trivial translations from page to folio, mmap_sem to mmap_lock - Replace pmd_trans_unstable() with pte_offset_map_nolock() and handle its possible failure - Move pte mapping into remap_pages_pte to allow for retries when source page or anon_vma is contended. Since pte_offset_map_nolock() start RCU read section, we can't block anymore after mapping a pte, so have to unmap the ptesm do the locking and retry. - Add and use anon_vma_trylock_write() to avoid blocking while in RCU read section. - Accommodate changes in mmu_notifier_range_init() API, switch to mmu_notifier_invalidate_range_start_nonblock() to avoid blocking while in RCU read section. - Open-code now removed __swp_swapcount() - Replace pmd_read_atomic() with pmdp_get_lockless() - Add new selftest for UFFDIO_MOVE [1] https://gitlab.com/aarcange/aa/-/commit/2aec7aea56b10438a3881a20a411aa4b1fc19e92 [2] https://lore.kernel.org/all/1425575884-2574-1-git-send-email-aarcange@redhat.com/ [3] https://lore.kernel.org/linux-mm/CA+EESO4uO84SSnBhArH4HvLNhaUQ5nZKNKXqxRCyjniNVjp0Aw@mail.gmail.com/ [4] https://lore.kernel.org/all/20230914152620.2743033-1-surenb@google.com/ [5] https://lore.kernel.org/all/20230923013148.1390521-1-surenb@google.com/ [6] https://lore.kernel.org/all/1425575884-2574-21-git-send-email-aarcange@redhat.com/ [7] https://lore.kernel.org/all/cover.1547251023.git.blake.caldwell@colorado.edu/ [8] https://lore.kernel.org/all/20231009064230.2952396-1-surenb@google.com/ The patchset applies over mm-unstable. Andrea Arcangeli (2): mm/rmap: support move to different root anon_vma in folio_move_anon_rmap() userfaultfd: UFFDIO_MOVE uABI Suren Baghdasaryan (3): selftests/mm: call uffd_test_ctx_clear at the end of the test selftests/mm: add uffd_test_case_ops to allow test case-specific operations selftests/mm: add UFFDIO_MOVE ioctl test Documentation/admin-guide/mm/userfaultfd.rst | 3 + fs/userfaultfd.c | 72 +++ include/linux/rmap.h | 5 + include/linux/userfaultfd_k.h | 11 + include/uapi/linux/userfaultfd.h | 29 +- mm/huge_memory.c | 122 ++++ mm/khugepaged.c | 3 + mm/rmap.c | 30 + mm/userfaultfd.c | 596 +++++++++++++++++++ tools/testing/selftests/mm/uffd-common.c | 51 +- tools/testing/selftests/mm/uffd-common.h | 11 + tools/testing/selftests/mm/uffd-stress.c | 5 +- tools/testing/selftests/mm/uffd-unit-tests.c | 144 +++++ 13 files changed, 1078 insertions(+), 4 deletions(-)