[RFC PATCH v4 0/5] Readahead tweaks for larger folios

[Ryan Roberts <ryan.roberts@arm.com>]

Hi All,

This RFC series adds some tweaks to readahead so that it does a better job of
ramping up folio sizes as readahead extends further into the file. And it
additionally special-cases executable mappings to allow the arch to request a
preferred folio size for text.

Previous versions of the series focussed on the latter part only (large folios
for text). See [3]. But after discussion with Matthew Wilcox last week, we
decided that we should really be fixing some of the unintended behaviours in how
a folio size is selected in general before special-casing for text. As a result
patches 1-4 make folio size selection behave more sanely, then patch 5
introduces large folios for text. Patch 5 depends on patch 1, but does not
depend on patches 2-4.

---

I'm leaving this marked as RFC for now as I intend to do more testing, and
haven't yet updated the benchmark results in patch 5 (although I expect them to
be similar).

Applies on top of Monday's mm-unstable (b18dec6a6ad3) and passes all mm
kselftests.

Changes since v3 [3]
====================

 - Added patchs 1-4 to do better job of ramping up folio order
 - In patch 5:
   - Confine readahead blocks to vma boundaries (per Kalesh)
   - Rename arch_exec_folio_order() to exec_folio_order() (per Matthew)
   - exec_folio_order() now returns unsigned int and defaults to order-0
     (per Matthew)
   - readahead size is honoured (including when disabled)

Changes since v2 [2]
====================

 - Rename arch_wants_exec_folio_order() to arch_exec_folio_order() (per Andrew)
 - Fixed some typos (per Andrew)

Changes since v1 [1]
====================

 - Remove "void" from arch_wants_exec_folio_order() macro args list

[1] https://lore.kernel.org/linux-mm/20240111154106.3692206-1-ryan.roberts@arm.com/
[2] https://lore.kernel.org/all/20240215154059.2863126-1-ryan.roberts@arm.com/
[3] https://lore.kernel.org/linux-mm/20250327160700.1147155-1-ryan.roberts@arm.com/

Thanks,
Ryan

Ryan Roberts (5):
  mm/readahead: Honour new_order in page_cache_ra_order()
  mm/readahead: Terminate async readahead on natural boundary
  mm/readahead: Make space in struct file_ra_state
  mm/readahead: Store folio order in struct file_ra_state
  mm/filemap: Allow arch to request folio size for exec memory

 arch/arm64/include/asm/pgtable.h |  8 +++++
 include/linux/fs.h               |  4 ++-
 include/linux/pgtable.h          | 11 +++++++
 mm/filemap.c                     | 55 ++++++++++++++++++++++++--------
 mm/internal.h                    |  3 +-
 mm/readahead.c                   | 27 +++++++++-------
 6 files changed, 81 insertions(+), 27 deletions(-)

--
2.43.0