mm: Page fault accounting cleanups

v4:
- rebase to linux-next/akpm
- picked one more r-b

v3:
- comment fixes [Gerald]
- check VM_FAULT_ERROR too [Gerald]
- collect r-b

==================== cover letter for v2 =============================

This is v2 of the pf accounting cleanup series. It originates from Gerald Schaefer's report on an issue a week ago regarding to incorrect page fault accountings for retried page fault after commit 4064b9827063 ("mm: allow VM_FAULT_RETRY for multiple times"):

https://lore.kernel.org/lkml/20200610174811.44b94525@thinkpad/

This version used a better approach suggested by Linus so that we do accounting directly in handle_mm_fault(). Moreover, we'll cover some special accounting too like gup or IOMMU fault requests on process page tables. The outcome of this series is to keep all the pf accountings in handle_mm_fault() (besides PERF_COUNT_SW_PAGE_FAULTS, which is still done in per-arch #pf handlers).

Since v2 changed quite a lot from v1, changelog is omitted, and I also didn't have a chance to pick up any r-b in previous version. I really appreciate anyone who has looked at v1. V1 for reference:

https://lore.kernel.org/lkml/[email protected]/

What this series did:

- Correct page fault accounting: we do accounting for a page fault (no matter whether it's from #PF handling, or gup, or anything else) only with the one that completed the fault. For example, page fault retries should not be counted in page fault counters. Same to the perf events.

- Unify definition of PERF_COUNT_SW_PAGE_FAULTS: currently this perf event is used in an adhoc way across different archs.

Case (1): for many archs it's done at the entry of a page fault handler, so that it will also cover e.g. errornous faults.

Case (2): for some other archs, it is only accounted when the page fault is resolved successfully.

Case (3): there're still quite some archs that have not enabled this perf event.

Since this series will touch merely all the archs, we unify this perf event to always follow case (1), which is the one that makes most sense. And since we moved the accounting into handle_mm_fault, the other two MAJ/MIN perf events are well taken care of naturally.

- Unify definition of "major faults": the definition of "major fault" is slightly changed when used in accounting (not VM_FAULT_MAJOR). More information in patch 1.

- Always account the page fault onto the one that triggered the page fault. This does not matter much for #PF handlings, but mostly for gup. More information on this in patch 25.

Patchset layout:

Patch 1:     Introduced the accounting in handle_mm_fault(), not enabled.
Patch 2-24:  Enable the new accounting for arch #PF handlers one by one.
Patch 25:    Enable the new accounting for the rest outliers (gup, iommu, etc.)
Patch 26:    Cleanup GUP task_struct pointer since it's not needed any more

For each of the patch that fixes a specific arch, I'm CCing the maintainers and the arch list if there is. Besides, I only lightly tested this series on x86.

Please have a look, thanks.

Peter Xu (26):
mm: Do page fault accounting in handle_mm_fault mm/alpha: Use general page fault accounting mm/arc: Use general page fault accounting mm/arm: Use general page fault accounting mm/arm64: Use general page fault accounting mm/csky: Use general page fault accounting mm/hexagon: Use general page fault accounting mm/ia64: Use general page fault accounting mm/m68k: Use general page fault accounting mm/microblaze: Use general page fault accounting mm/mips: Use general page fault accounting mm/nds32: Use general page fault accounting mm/nios2: Use general page fault accounting mm/openrisc: Use general page fault accounting mm/parisc: Use general page fault accounting mm/powerpc: Use general page fault accounting mm/riscv: Use general page fault accounting mm/s390: Use general page fault accounting mm/sh: Use general page fault accounting mm/sparc32: Use general page fault accounting mm/sparc64: Use general page fault accounting mm/unicore32: Use general page fault accounting mm/x86: Use general page fault accounting mm/xtensa: Use general page fault accounting
mm: Clean up the last pieces of page fault accountings mm/gup: Remove task_struct pointer for all gup code

 arch/alpha/mm/fault.c                       |   8 +-
 arch/arc/kernel/process.c                   |   2 +-
 arch/arc/mm/fault.c                         |  18 +---
 arch/arm/mm/fault.c                         |  25 ++---
 arch/arm64/mm/fault.c                       |  29 ++----
 arch/csky/mm/fault.c                        |  13 +--
 arch/hexagon/mm/vm_fault.c                  |   9 +-
 arch/ia64/mm/fault.c                        |   9 +-
 arch/m68k/mm/fault.c                        |  14 +--
 arch/microblaze/mm/fault.c                  |   9 +-
 arch/mips/mm/fault.c                        |  14 +--
 arch/nds32/mm/fault.c                       |  19 +---
 arch/nios2/mm/fault.c                       |  14 +--
 arch/openrisc/mm/fault.c                    |   9 +-
 arch/parisc/mm/fault.c                      |   8 +-
 arch/powerpc/mm/copro_fault.c               |   7 +-
 arch/powerpc/mm/fault.c                     |  11 +-
 arch/riscv/mm/fault.c                       |  16 +--
 arch/s390/kvm/interrupt.c                   |   2 +-
 arch/s390/kvm/kvm-s390.c                    |   2 +-
 arch/s390/kvm/priv.c                        |   8 +-
 arch/s390/mm/fault.c                        |  16 +--
 arch/s390/mm/gmap.c                         |   4 +-
 arch/sh/mm/fault.c                          |  11 +-
 arch/sparc/mm/fault_32.c                    |  13 +--
 arch/sparc/mm/fault_64.c                    |  11 +-
 arch/um/kernel/trap.c                       |   6 +-
 arch/unicore32/mm/fault.c                   |  14 +--
 arch/x86/mm/fault.c                         |  17 +--
 arch/xtensa/mm/fault.c                      |  15 +--
 drivers/gpu/drm/i915/gem/i915_gem_userptr.c |   2 +-
 drivers/infiniband/core/umem_odp.c          |   2 +-
 drivers/iommu/amd/iommu_v2.c                |   2 +-
 drivers/iommu/intel/svm.c                   |   3 +-
 drivers/vfio/vfio_iommu_type1.c             |   4 +-
 fs/exec.c                                   |   2 +-
 include/linux/mm.h                          |  16 +--
 kernel/events/uprobes.c                     |   6 +-
 kernel/futex.c                              |   2 +-
 mm/gup.c                                    | 109 +++++++-------------
 mm/hmm.c                                    |   3 +-
 mm/ksm.c                                    |   3 +-
 mm/memory.c                                 |  69 ++++++++++++-
 mm/process_vm_access.c                      |   2 +-
 security/tomoyo/domain.c                    |   2 +-
 virt/kvm/async_pf.c                         |   2 +-
 virt/kvm/kvm_main.c                         |   2 +-
 47 files changed, 222 insertions(+), 362 deletions(-)

2.26.2

I fixed some stuff in the send scripts but definitely broke something else on the chaining of the messages. Andrew, please let me know if you want me to resend... Sorry for that.

Peter Xu

Well, the words

: Since v2 changed quite a lot from v1, changelog is omitted, and I also : didn't have a chance to pick up any r-b in previous version. I really : appreciate anyone who has looked at v1. V1 for reference:

make me think "not yet". But this patchset is v4, so all confused.

I'm thinking we give this v4 a week for people to check it over, gather up the revews and acks, incorporate the change suggested by David, redo and double-check the cover letter then shoot for a v5?

I posted v2 & v3 with incorrect versioning, so they were all shown as v1 in the subjects. I fixed it in v4 so it seemed to have jumped from v1->v4. Sorry for the confusion.

Regarding to the cover letter: I rewrote the cover letter in v2 because it changed a lot. While v3 & v4 changed little, so I kept the v2 cover letter then appended with changelogs for v3/v4 at the top because the content of the v2 cover letter still stand.

Will do. Thanks,

Peter Xu