Re: [PATCH 03/12] mm: hugetlb_vmemmap: simplify vmemmap head page handling

[Lance Yang]

On Tue, Oct 20, 2026 at 07:58:15PM +0800, Muchun Song wrote:
>The new head page is already tracked on the vmemmap page list before
>remapping starts.  Passing it separately gives the remap walker two
>ways to refer to the same page and unnecessarily complicates its
>interface.
>
>Use the page list as the single handoff mechanism for the head page,
>removing the redundant state from the walker.
>
>No functional change intended.
>
>Signed-off-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
>---
> mm/hugetlb_vmemmap.c | 17 +++++++----------
> 1 file changed, 7 insertions(+), 10 deletions(-)
>
>diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c
>index 8b3abb562599..164e93e980bf 100644
>--- a/mm/hugetlb_vmemmap.c
>+++ b/mm/hugetlb_vmemmap.c
>@@ -25,7 +25,6 @@
>  *
>  * @remap_pte:		called for each lowest-level entry (PTE).
>  * @nr_walked:		the number of walked pte.
>- * @vmemmap_head:	the page to be installed as first in the vmemmap range
>  * @vmemmap_tail:	the page to be installed as non-first in the vmemmap range
>  * @vmemmap_pages:	the list head of the vmemmap pages that can be freed
>  *			or is mapped from.
>@@ -37,7 +36,6 @@ struct vmemmap_remap_walk {
> 					     struct vmemmap_remap_walk *walk);
> 
> 	unsigned long		nr_walked;
>-	struct page		*vmemmap_head;
> 	struct page		*vmemmap_tail;
> 	struct list_head	*vmemmap_pages;
> 
>@@ -208,10 +206,13 @@ static void vmemmap_remap_pte(pte_t *pte, unsigned long addr,
> 	pte_t entry;
> 
> 	/* Remapping the head page requires r/w */
>-	if (unlikely(walk->nr_walked == 0 && walk->vmemmap_head)) {
>+	if (unlikely(walk->nr_walked == 0)) {
>+		struct page *head;
>+
> 		VM_WARN_ON_ONCE(!PageHead((const struct page *)addr));
> 
>-		list_del(&walk->vmemmap_head->lru);
>+		head = list_first_entry(walk->vmemmap_pages, struct page, lru);
>+		list_del(&head->lru);
> 
> 		/*
> 		 * Makes sure that preceding stores to the page contents from
>@@ -220,7 +221,7 @@ static void vmemmap_remap_pte(pte_t *pte, unsigned long addr,
> 		 */
> 		smp_wmb();
> 
>-		entry = mk_pte(walk->vmemmap_head, PAGE_KERNEL);
>+		entry = mk_pte(head, PAGE_KERNEL);
> 	} else {
> 		VM_WARN_ON_ONCE(!PageTail((const struct page *)addr));
> 
>@@ -289,7 +290,6 @@ static int vmemmap_remap_split(unsigned long start, unsigned long end)
>  *		to remap.
>  * @end:	end address of the vmemmap virtual address range that we want to
>  *		remap.
>- * @vmemmap_head: the page to be installed as first in the vmemmap range
>  * @vmemmap_tail: the page to be installed as non-first in the vmemmap range
>  * @vmemmap_pages: list to deposit vmemmap pages to be freed.  It is callers
>  *		responsibility to free pages.
>@@ -298,7 +298,6 @@ static int vmemmap_remap_split(unsigned long start, unsigned long end)
>  * Return: %0 on success, negative error code otherwise.
>  */


/**
 * vmemmap_remap_free - remap the vmemmap virtual address range [@start, @end)
 *			to use @vmemmap_head/tail, then free vmemmap which
 *			the range are mapped to.

Nit: could you update the @vmemmap_head/tail comment too, now that the
head argument is gone?

Nothing jumped out at me, so

Reviewed-by: Lance Yang <lance.yang@xxxxxxxxx>