When per-vma locks were introduced in [1] several types of page faults would still fall back to mmap_lock to keep the patchset simple. Among them are swap and userfault pages. The main reason for skipping those cases was the fact that mmap_lock could be dropped while handling these faults and that required additional logic to be implemented. Implement the mechanism to allow per-vma locks to be dropped for these cases. When that happens handle_mm_fault returns new VM_FAULT_VMA_UNLOCKED vm_fault_reason bit along with VM_FAULT_RETRY to indicate that VMA lock was dropped. Naturally, once VMA lock is dropped that VMA should be assumed unstable and can't be used. Changes since v1 posted at [2] - New patch 1/6 to remove do_poll parameter from read_swap_cache_async(), per Huang Ying - New patch 3/6 to separate VM_FAULT_COMPLETED addition, per Alistair Popple - Added comment for VM_FAULT_VMA_UNLOCKED in 4/6, per Alistair Popple - New patch 6/6 to handle userfaults under VMA lock Note: I tried implementing Matthew's suggestion in [3] to add vmf_end_read but that gets quite messy since it would require changing code for every architecture when we change handle_mm_fault interface. Note: patch 4/6 will cause a trivial merge conflict in arch/arm64/mm/fault.c when applied over mm-unstable branch due to a patch from ARM64 tree [4] which is missing in mm-unstable. [1] https://lore.kernel.org/all/20230227173632.3292573-1-surenb@xxxxxxxxxx/ [2] https://lore.kernel.org/all/20230501175025.36233-1-surenb@xxxxxxxxxx/ [3] https://lore.kernel.org/all/ZFEeHqzBJ6iOsRN+@xxxxxxxxxxxxxxxxxxxx/ [4] https://lore.kernel.org/all/20230524131305.2808-1-jszhang@xxxxxxxxxx/ Suren Baghdasaryan (6): swap: remove remnants of polling from read_swap_cache_async mm: handle swap page faults under VMA lock if page is uncontended mm: add missing VM_FAULT_RESULT_TRACE name for VM_FAULT_COMPLETED mm: drop VMA lock before waiting for migration mm: implement folio wait under VMA lock mm: handle userfaults under VMA lock arch/arm64/mm/fault.c | 3 ++- arch/powerpc/mm/fault.c | 3 ++- arch/s390/mm/fault.c | 3 ++- arch/x86/mm/fault.c | 3 ++- fs/userfaultfd.c | 42 ++++++++++++++++++----------------- include/linux/mm_types.h | 7 +++++- include/linux/pagemap.h | 14 ++++++++---- mm/filemap.c | 37 +++++++++++++++++++------------ mm/madvise.c | 4 ++-- mm/memory.c | 48 ++++++++++++++++++++++------------------ mm/swap.h | 1 - mm/swap_state.c | 12 +++++----- 12 files changed, 103 insertions(+), 74 deletions(-) -- 2.41.0.162.gfafddb0af9-goog
