Re: [PATCH v5 1/3] mm/vmalloc: extract vm_area_free_pages() helper from vfree()

Uladzislau Rezki
2026-03-18T17:53:14Z

On Tue, Mar 17, 2026 at 01:47:33PM +0530, Shivam Kalra via B4 Relay wrote:
> From: Shivam Kalra <shivamkalra98@zohomail.in>
>
> Extract the page-freeing loop and NR_VMALLOC stat accounting from
> vfree() into a reusable vm_area_free_pages() helper. The helper operates
> on a range [start, end) of pages from a vm_struct, making it suitable
> for both full free (vfree) and partial free (upcoming vrealloc shrink).
>
> Freed page pointers in vm->pages[] are set to NULL to prevent stale
> references when the vm_struct outlives the free (as in vrealloc shrink).
>
> Signed-off-by: Shivam Kalra <shivamkalra98@zohomail.in>
> ---
> mm/vmalloc.c | 47 +++++++++++++++++++++++++++++++++--------------
> 1 file changed, 33 insertions(+), 14 deletions(-)
>
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index c607307c657a..b29bf58c0e3f 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -3416,6 +3416,38 @@ void vfree_atomic(const void *addr)
> schedule_work(&p->wq);
> }
>
> +/*
> + * vm_area_free_pages - free a range of pages from a vmalloc allocation
> + * @vm: the vm_struct containing the pages
> + * @start: first page index to free (inclusive)
> + * @end: last page index to free (exclusive)
> + *
> + * Free pages [start, end) updating NR_VMALLOC stat accounting.
> + * Freed vm->pages[] entries are set to NULL.
> + * Caller is responsible for unmapping (vunmap_range) and KASAN
> + * poisoning before calling this.
> + */
> +static void vm_area_free_pages(struct vm_struct *vm, unsigned int start,
> + unsigned int end)
> +{
> + unsigned int i;
> +
> + for (i = start; i < end; i++) {
> + struct page *page = vm->pages[i];
> +
> + BUG_ON(!page);
> + /*
> + * High-order allocs for huge vmallocs are split, so
> + * can be freed as an array of order-0 allocations
> + */
> + if (!(vm->flags & VM_MAP_PUT_PAGES))
> + mod_lruvec_page_state(page, NR_VMALLOC, -1);
> + __free_page(page);
> + vm->pages[i] = NULL;
> + cond_resched();
> + }
> +}
> +
>
Since you will update second patch, probably you can also improve this
one. To me start/end variables sound like a VA range whereas it is
indices in the array.

Any thoughts?

--
Uladzislau Rezki