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Message-ID: <20230628071800.544800-1-surenb@google.com>
Date: Wed, 28 Jun 2023 00:17:54 -0700
From: Suren Baghdasaryan <surenb@...gle.com>
To: akpm@...ux-foundation.org
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Subject: [PATCH v4 0/6] Per-VMA lock support for swap and userfaults
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 v3 posted at [2]
- Renamed folio_lock_or_retry back to folio_lock_fault, per Peter Xu
- Moved per-VMA lock release to where VM_FAULT_RETRY is returned,
per Peter Xu
- Dropped FAULT_FLAG_LOCK_DROPPED usage, per Peter Xu
- Introduced release_fault_lock() helper function, per Peter Xu
- Dropped the patch releasing per-VMA lock before migration_entry_wait,
per Peter Xu
- Introduced assert_fault_locked() helper function, per Peter Xu
- Added BUG_ON to prevent FAULT_FLAG_RETRY_NOWAIT usage with per-VMA locks
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/20230627042321.1763765-1-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 | 39 ++++++++++++++++++---------------------
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 | 38 ++++++++++++++++----------------------
mm/swap.h | 1 -
mm/swap_state.c | 12 +++++-------
13 files changed, 113 insertions(+), 81 deletions(-)
--
2.41.0.162.gfafddb0af9-goog
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