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

Ryan Roberts
2025-05-06T11:53:07Z

On 30/04/2025 15:59, Ryan Roberts wrote:
> 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).

Thanks Jan, David and Anshuman for the reviews! I'll do the suggested changes
and complete my testing, then aim to post again against -rc1, to hopefully get
it into linux-next.

Thanks,
Ryan

>
> 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
>