Re: [PATCH mm-unstable v1 3/5] mm/khugepaged: define COLLAPSE_MAX_PTES_LIMIT as HPAGE_PMD_NR - 1

Pedro Falcato
2026-02-12T14:45:37Z

On Wed, Feb 11, 2026 at 07:18:33PM -0700, Nico Pache wrote:
> The value (HPAGE_PMD_NR - 1) is used often in the khugepaged code to
> signify the limit of the max_ptes_* values. Add a define for this to
> increase code readability and reuse.
>
> Signed-off-by: Nico Pache <npache@redhat.com>

Acked-by: Pedro Falcato <pfalcato@suse.de>

> ---
> mm/khugepaged.c | 15 ++++++++-------
> 1 file changed, 8 insertions(+), 7 deletions(-)
>
> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> index c362b3b2e08a..3dcce6018f20 100644
> --- a/mm/khugepaged.c
> +++ b/mm/khugepaged.c
> @@ -85,6 +85,7 @@ static DECLARE_WAIT_QUEUE_HEAD(khugepaged_wait);
> *
> * Note that these are only respected if collapse was initiated by khugepaged.
> */
> +#define COLLAPSE_MAX_PTES_LIMIT (HPAGE_PMD_NR - 1)
> unsigned int khugepaged_max_ptes_none __read_mostly;
> static unsigned int khugepaged_max_ptes_swap __read_mostly;
> static unsigned int khugepaged_max_ptes_shared __read_mostly;
> @@ -252,7 +253,7 @@ static ssize_t max_ptes_none_store(struct kobject *kobj,
> unsigned long max_ptes_none;
>
> err = kstrtoul(buf, 10, &max_ptes_none);
> - if (err || max_ptes_none > HPAGE_PMD_NR - 1)
> + if (err || max_ptes_none > COLLAPSE_MAX_PTES_LIMIT)
> return -EINVAL;
>
> khugepaged_max_ptes_none = max_ptes_none;
> @@ -277,7 +278,7 @@ static ssize_t max_ptes_swap_store(struct kobject *kobj,
> unsigned long max_ptes_swap;
>
> err = kstrtoul(buf, 10, &max_ptes_swap);
> - if (err || max_ptes_swap > HPAGE_PMD_NR - 1)
> + if (err || max_ptes_swap > COLLAPSE_MAX_PTES_LIMIT)
> return -EINVAL;
>
> khugepaged_max_ptes_swap = max_ptes_swap;
> @@ -303,7 +304,7 @@ static ssize_t max_ptes_shared_store(struct kobject *kobj,
> unsigned long max_ptes_shared;
>
> err = kstrtoul(buf, 10, &max_ptes_shared);
> - if (err || max_ptes_shared > HPAGE_PMD_NR - 1)
> + if (err || max_ptes_shared > COLLAPSE_MAX_PTES_LIMIT)
> return -EINVAL;
>
> khugepaged_max_ptes_shared = max_ptes_shared;
> @@ -384,7 +385,7 @@ int __init khugepaged_init(void)
> return -ENOMEM;
>
> khugepaged_pages_to_scan = HPAGE_PMD_NR * 8;
> - khugepaged_max_ptes_none = HPAGE_PMD_NR - 1;
> + khugepaged_max_ptes_none = COLLAPSE_MAX_PTES_LIMIT;
> khugepaged_max_ptes_swap = HPAGE_PMD_NR / 8;
> khugepaged_max_ptes_shared = HPAGE_PMD_NR / 2;
>
> @@ -1869,7 +1870,7 @@ static enum scan_result collapse_file(struct mm_struct *mm, unsigned long addr,
> bool is_shmem = shmem_file(file);
>
> VM_BUG_ON(!IS_ENABLED(CONFIG_READ_ONLY_THP_FOR_FS) && !is_shmem);
> - VM_BUG_ON(start & (HPAGE_PMD_NR - 1));
> + VM_BUG_ON(start & (COLLAPSE_MAX_PTES_LIMIT));

nit: no need for the () around COLLAPSE_MAX_PTES_LIMIT here

--
Pedro