[PATCH 00/26] mm: Page fault accounting cleanups

Peter Xu
2020-06-19T16:08:29Z

(Forgot to cc mm list on v1; adding in)

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/20200615221607.7764-1-peterx@redhat.com/

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 | 2 +-
drivers/vfio/vfio_iommu_type1.c | 2 +-
fs/exec.c | 2 +-
include/linux/mm.h | 16 +--
kernel/events/uprobes.c | 6 +-
kernel/futex.c | 2 +-
mm/gup.c | 107 +++++++-------------
mm/hmm.c | 3 +-
mm/ksm.c | 3 +-
mm/memory.c | 72 ++++++++++++-
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(+), 360 deletions(-)

--
2.26.2