[PATCH v5 0/6] Per-VMA lock support for swap and userfaults

Suren Baghdasaryan
2023-06-28T17:25:37Z

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.
First, change handle_mm_fault to drop per-VMA locks when returning
VM_FAULT_RETRY or VM_FAULT_COMPLETED to be consistent with the way
mmap_lock is handled. Then change folio_lock_or_retry to accept vm_fault
and return vm_fault_t which simplifies later patches. Finally allow swap
and uffd page faults to be handled under per-VMA locks by dropping per-VMA
and retrying, the same way it's done under mmap_lock.
Naturally, once VMA lock is dropped that VMA should be assumed unstable
and can't be used.

Changes since v4 posted at [2]
- 5/6 changed setting VM_FAULT_RETRY bit to an assignment, per Peter Xu
- 5/6 moved release_fault_lock to its final place, per Peter Xu
- 6/6 removed mm parameter in assert_fault_locked, per Peter Xu
- 6/6 replaced BUG_ON with WARN_ON_ONCE and moved the check for
FAULT_FLAG_RETRY_NOWAIT && FAULT_FLAG_VMA_LOCK into sanitize_fault_flags,
per Peter Xu

Note: patch 3/8 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 [3]
which is missing in mm-unstable.

[1] https://lore.kernel.org/all/20230227173632.3292573-1-surenb@google.com/
[2] https://lore.kernel.org/all/20230628071800.544800-1-surenb@google.com/
[3] https://lore.kernel.org/all/20230524131305.2808-1-jszhang@kernel.org/

Suren Baghdasaryan (6):
swap: remove remnants of polling from read_swap_cache_async
mm: add missing VM_FAULT_RESULT_TRACE name for VM_FAULT_COMPLETED
mm: drop per-VMA lock when returning VM_FAULT_RETRY or
VM_FAULT_COMPLETED
mm: change folio_lock_or_retry to use vm_fault directly
mm: handle swap page faults under per-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 | 34 ++++++++++++----------------
include/linux/mm.h | 39 ++++++++++++++++++++++++++++++++
include/linux/mm_types.h | 3 ++-
include/linux/pagemap.h | 9 ++++----
mm/filemap.c | 37 +++++++++++++++---------------
mm/madvise.c | 4 ++--
mm/memory.c | 49 ++++++++++++++++++++++------------------
mm/swap.h | 1 -
mm/swap_state.c | 12 ++++------
13 files changed, 120 insertions(+), 80 deletions(-)