Re: [PATCH 1/2] Docs/ABI: document transparent_hugepage/shrink_underused

[Lorenzo Stoakes (ARM)]

Please don't send patch series like this - we really require a cover letter if
patch count > 1, and every patch should reply to the cover letter.

On Wed, Aug 12, 2026 at 04:03:12PM +0800, Song Hu wrote:
> The shrink_underused knob was added in commit 81d3ff3c6f76 ("mm: add
> sysfs entry to disable splitting underused THPs") but is missing from
> Documentation/ABI/testing/sysfs-kernel-mm-transparent-hugepage, although
> transhuge.rst already documents it.  Add the ABI entry.

Hmm what even is this file? :) What is the contract on this file?

>
> Signed-off-by: Song Hu <husong@xxxxxxxxxx>
> ---
>  .../ABI/testing/sysfs-kernel-mm-transparent-hugepage   | 10 ++++++++++
>  1 file changed, 10 insertions(+)
>
> diff --git a/Documentation/ABI/testing/sysfs-kernel-mm-transparent-hugepage b/Documentation/ABI/testing/sysfs-kernel-mm-transparent-hugepage
> index 7bfbb9cc2c11..bbdfae2c0caa 100644
> --- a/Documentation/ABI/testing/sysfs-kernel-mm-transparent-hugepage
> +++ b/Documentation/ABI/testing/sysfs-kernel-mm-transparent-hugepage
> @@ -10,9 +10,19 @@ Description:
>  			- hpage_pmd_size
>  			- khugepaged
>  			- shmem_enabled
> +			- shrink_underused

I mean I guess fine for consistency.

>  			- use_zero_page
>  			- subdirectories of the form hugepages-<size>kB, where <size>
>  			  is the page size of the hugepages supported by the kernel/CPU
>  			  combination.

But we already handwave literally everything else here....


>
>  		See Documentation/admin-guide/mm/transhuge.rst for details.
> +
> +What:		/sys/kernel/mm/transparent_hugepage/shrink_underused
> +Date:		Sep 2024
> +Contact:	Linux memory management mailing list <linux-mm@xxxxxxxxx>
> +Description:	Reading and writing this file controls whether khugepaged
> +		splits underused transparent huge pages (THPs) under memory
> +		pressure.  A THP is considered underused when its number of
> +		zero-filled pages is above max_ptes_none.  Enabled by default;
> +		writing 0 disables the splitting and 1 enables it.

Nothing else is documented in this file so why is this getting special
treatment? And why is it backdated to Sep 2024?...

Drop it please.

> --
> 2.43.0
>

--
Cheers, Lorenzo