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

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Message-ID: <2a90ec6c-1725-4c32-8819-c46e8c0e4630@arm.com>
Date: Tue, 6 May 2025 11:05:34 +0100
From: Ryan Roberts <ryan.roberts@....com>
To: Andrew Morton <akpm@...ux-foundation.org>,
 "Matthew Wilcox (Oracle)" <willy@...radead.org>,
 Alexander Viro <viro@...iv.linux.org.uk>,
 Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>,
 David Hildenbrand <david@...hat.com>, Dave Chinner <david@...morbit.com>,
 Catalin Marinas <catalin.marinas@....com>, Will Deacon <will@...nel.org>,
 Kalesh Singh <kaleshsingh@...gle.com>, Zi Yan <ziy@...dia.com>
Cc: linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
 linux-fsdevel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [RFC PATCH v4 0/5] Readahead tweaks for larger folios

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
>