Re: [PATCH 04/12] mm/collapse: add collapse.h for the collapse interface

[Baolin Wang]

On 9/4/26 11:10 PM, Kiryl Shutsemau wrote:
> From: "Kiryl Shutsemau (Meta)" <kas@xxxxxxxxxx>
>
> khugepaged.c holds both the users of collapse and the machinery that
> performs it.  The daemon's scan loop, the sysfs tunables, MADV_COLLAPSE's
> entry point and the collapse itself all sit in one file and reach into
> each other freely.  Nothing marks where a user ends and the engine
> begins.
>
> Start drawing that line.
>
> Add mm/collapse.h for what the two sides have to agree on:
>
>    - enum scan_result - what the engine hands back;
>    - struct collapse_control - the state a request carries.
>
> And two constants move with them:
>
>    - KHUGEPAGED_MAX_PTES_LIMIT -> COLLAPSE_MAX_PTES_LIMIT;
>    - KHUGEPAGED_MIN_MTHP_ORDER -> COLLAPSE_MIN_MTHP_ORDER.
>
> Neither is a fact about the daemon, so both lose the KHUGEPAGED_ prefix.
>
> No functional change.
>
> Assisted-by: Claude-Code:claude-opus-5
> Signed-off-by: Kiryl Shutsemau (Meta) <kas@xxxxxxxxxx>
> ---
>   MAINTAINERS     |  1 +
>   mm/collapse.h   | 67 +++++++++++++++++++++++++++++++++++++++++
>   mm/khugepaged.c | 79 ++++++++-----------------------------------------
>   3 files changed, 81 insertions(+), 66 deletions(-)
>   create mode 100644 mm/collapse.h
>
> diff --git a/MAINTAINERS b/MAINTAINERS
> index a9245d827ddb..4d1ff4c76496 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -17433,6 +17433,7 @@ F:	Documentation/admin-guide/mm/transhuge.rst
>   F:	include/linux/huge_mm.h
>   F:	include/linux/khugepaged.h
>   F:	include/trace/events/huge_memory.h
> +F:	mm/collapse.h
>   F:	mm/huge_memory.c
>   F:	mm/khugepaged.c
>   F:	mm/mm_slot.h
> diff --git a/mm/collapse.h b/mm/collapse.h
> new file mode 100644
> index 000000000000..1c40229b9554
> --- /dev/null
> +++ b/mm/collapse.h
> @@ -0,0 +1,67 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#ifndef __MM_COLLAPSE_H
> +#define __MM_COLLAPSE_H
> +
> +#include <linux/mm.h>
> +#include <linux/nodemask.h>
> +#include <linux/pgtable.h>
> +#include <linux/types.h>
> +
> +/* The most the max_ptes_* tunables accept */
> +#define COLLAPSE_MAX_PTES_LIMIT		(HPAGE_PMD_NR - 1)
> +
> +/* The smallest order a collapse will build */
> +#define COLLAPSE_MIN_MTHP_ORDER		2

These 2 macros are already self-explanatory, and the comments are 
over-documented. I'd prefer to drop them. With that,

Reviewed-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>