[PATCH v7 00/16] mm: folio_zero_user: clear contiguous pages

[Ankur Arora <ankur.a.arora@oracle.com>]

This series adds clearing of contiguous page ranges for hugepages,
improving on the current page-at-a-time approach in two ways:

 - amortizes the per-page setup cost over a larger extent

 - when using string instructions, exposes the real region size
   to the processor.

A processor could use a knowledge of the extent to optimize the
clearing. AMD Zen uarchs, as an example, elide allocation of
cachelines for regions larger than L3-size.

Demand faulting a 64GB region shows performance improvements:

 $ perf bench mem map -p $pg-sz -f demand -s 64GB -l 5

                 mm/folio_zero_user    x86/folio_zero_user       change
                  (GB/s  +- %stdev)     (GB/s  +- %stdev)

   pg-sz=2MB       11.82  +- 0.67%        16.48  +-  0.30%       + 39.4%	preempt=*

   pg-sz=1GB       17.14  +- 1.39%        17.42  +-  0.98% [#]   +  1.6%	preempt=none|voluntary
   pg-sz=1GB       17.51  +- 1.19%        43.23  +-  5.22%       +146.8%	preempt=full|lazy

[#] Milan uses a threshold of LLC-size (~32MB) for eliding cacheline
allocation, which is higher than the maximum extent used on x86
(ARCH_CONTIG_PAGE_NR=8MB), so preempt=none|voluntary sees no improvement
with pg-sz=1GB.

Raghavendra also tested v3/v4 on AMD Genoa and sees similar improvements [1].

Changelog:

v7:
 - interface cleanups, comments for clear_user_highpages(), clear_user_pages(),
   clear_pages().
 - fixed build errors flagged by kernel test robot
 - move all x86 patches to the tail end

v6:
 - perf bench mem: update man pages and other cleanups (Namhyung Kim)
 - unify folio_zero_user() for HIGHMEM, !HIGHMEM options instead of
   working through a new config option (David Hildenbrand).
   - cleanups and simlification around that.
 (https://lore.kernel.org/lkml/20250902080816.3715913-1-ankur.a.arora@oracle.com/)

v5:
 - move the non HIGHMEM implementation of folio_zero_user() from x86
   to common code (Dave Hansen)
 - Minor naming cleanups, commit messages etc
 (https://lore.kernel.org/lkml/20250710005926.1159009-1-ankur.a.arora@oracle.com/)

v4:
 - adds perf bench workloads to exercise mmap() populate/demand-fault (Ingo)
 - inline stosb etc (PeterZ)
 - handle cooperative preemption models (Ingo)
 - interface and other cleanups all over (Ingo)
 (https://lore.kernel.org/lkml/20250616052223.723982-1-ankur.a.arora@oracle.com/)

v3:
 - get rid of preemption dependency (TIF_ALLOW_RESCHED); this version
   was limited to preempt=full|lazy.
 - override folio_zero_user() (Linus)
 (https://lore.kernel.org/lkml/20250414034607.762653-1-ankur.a.arora@oracle.com/)

v2:
 - addressed review comments from peterz, tglx.
 - Removed clear_user_pages(), and CONFIG_X86_32:clear_pages()
 - General code cleanup
 (https://lore.kernel.org/lkml/20230830184958.2333078-1-ankur.a.arora@oracle.com/)

Comments appreciated!

Also at:
  github.com/terminus/linux clear-pages.v7

[1] https://lore.kernel.org/lkml/fffd4dad-2cb9-4bc9-8a80-a70be687fd54@amd.com/

Ankur Arora (16):
  perf bench mem: Remove repetition around time measurement
  perf bench mem: Defer type munging of size to float
  perf bench mem: Move mem op parameters into a structure
  perf bench mem: Pull out init/fini logic
  perf bench mem: Switch from zalloc() to mmap()
  perf bench mem: Allow mapping of hugepages
  perf bench mem: Allow chunking on a memory region
  perf bench mem: Refactor mem_options
  perf bench mem: Add mmap() workloads
  mm: define clear_pages(), clear_user_pages()
  mm/highmem: introduce clear_user_highpages()
  arm: mm: define clear_user_highpages()
  mm: memory: support clearing page ranges
  x86/mm: Simplify clear_page_*
  x86/clear_page: Introduce clear_pages()
  x86/clear_pages: Support clearing of page-extents

 arch/arm/include/asm/page.h                  |   7 +
 arch/x86/include/asm/page_32.h               |   6 +
 arch/x86/include/asm/page_64.h               |  72 +++-
 arch/x86/lib/clear_page_64.S                 |  39 +-
 include/linux/highmem.h                      |  18 +
 include/linux/mm.h                           |  44 +++
 mm/memory.c                                  |  82 +++-
 tools/perf/Documentation/perf-bench.txt      |  58 ++-
 tools/perf/bench/bench.h                     |   1 +
 tools/perf/bench/mem-functions.c             | 390 ++++++++++++++-----
 tools/perf/bench/mem-memcpy-arch.h           |   2 +-
 tools/perf/bench/mem-memcpy-x86-64-asm-def.h |   4 +
 tools/perf/bench/mem-memset-arch.h           |   2 +-
 tools/perf/bench/mem-memset-x86-64-asm-def.h |   4 +
 tools/perf/builtin-bench.c                   |   1 +
 15 files changed, 560 insertions(+), 170 deletions(-)

-- 
2.43.5