mm/vma: introduce and use vmg_pages(), vmg_[start, end]_pgoff()

In the VMA logic we often need to determine the number of pages in the
specified merge range, as well as the start and end page offsets of that
range.

Introduce and use helpers for these purposes.

No functional change intended.

Link: https://lore.kernel.org/20260710-b4-pre-scalable-cow-v2-13-2a5aa403d977@kernel.org
Signed-off-by: Lorenzo Stoakes <ljs@kernel.org>
Reviewed-by: Pedro Falcato <pfalcato@suse.de>
Reviewed-by: Gregory Price <gourry@gourry.net>
Reviewed-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Cc: Ackerley Tng <ackerleytng@google.com>
Cc: David Hildenbrand (Arm) <david@kernel.org>
Cc: Kai Huang <kai.huang@intel.com>
Cc: Marek Szyprowski <m.szyprowski@samsung.com>
Cc: SJ Park <sj@kernel.org>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: Liam R. Howlett (Oracle) <liam@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

2 files changed, 21 insertions, 7 deletions

diff --git a/mm/vma.c b/mm/vma.c
index 35ba3475128f..995de8198fbb 100644
--- a/mm/vma.c
+++ b/mm/vma.c
@@ -197,11 +197,9 @@ static void init_multi_vma_prep(struct vma_prepare *vp,
  */
 static bool can_vma_merge_before(struct vma_merge_struct *vmg)
 {
-	pgoff_t pglen = PHYS_PFN(vmg->end - vmg->start);
-
 	if (is_mergeable_vma(vmg, /* merge_next = */ true) &&
 	    is_mergeable_anon_vma(vmg, /* merge_next = */ true)) {
-		if (vmg->next->vm_pgoff == vmg->pgoff + pglen)
+		if (vmg_end_pgoff(vmg) == vma_start_pgoff(vmg->next))
 			return true;
 	}
 
@@ -221,7 +219,7 @@ static bool can_vma_merge_after(struct vma_merge_struct *vmg)
 {
 	if (is_mergeable_vma(vmg, /* merge_next = */ false) &&
 	    is_mergeable_anon_vma(vmg, /* merge_next = */ false)) {
-		if (vmg->prev->vm_pgoff + vma_pages(vmg->prev) == vmg->pgoff)
+		if (vma_end_pgoff(vmg->prev) == vmg_start_pgoff(vmg))
 			return true;
 	}
 	return false;
@@ -759,7 +757,7 @@ static int commit_merge(struct vma_merge_struct *vmg)
 	 */
 	vma_adjust_trans_huge(vma, vmg->start, vmg->end,
 			      vmg->__adjust_middle_start ? vmg->middle : NULL);
-	vma_set_range(vma, vmg->start, vmg->end, vmg->pgoff);
+	vma_set_range(vma, vmg->start, vmg->end, vmg_start_pgoff(vmg));
 	vmg_adjust_set_range(vmg);
 	vma_iter_store_overwrite(vmg->vmi, vmg->target);
 
@@ -962,8 +960,7 @@ static __must_check struct vm_area_struct *vma_merge_existing_range(
 		 *    middle     next
 		 * shrink/delete extend
 		 */
-
-		pgoff_t pglen = PHYS_PFN(vmg->end - vmg->start);
+		const pgoff_t pglen = vmg_pages(vmg);
 
 		VM_WARN_ON_VMG(!merge_right, vmg);
 		/* If we are offset into a VMA, then prev must be middle. */
diff --git a/mm/vma.h b/mm/vma.h
index 8e4b61a7304c..527716c8739d 100644
--- a/mm/vma.h
+++ b/mm/vma.h
@@ -230,6 +230,23 @@ static inline bool vmg_nomem(struct vma_merge_struct *vmg)
 	return vmg->state == VMA_MERGE_ERROR_NOMEM;
 }
 
+static inline pgoff_t vmg_start_pgoff(const struct vma_merge_struct *vmg)
+{
+	return vmg->pgoff;
+}
+
+static inline pgoff_t vmg_pages(const struct vma_merge_struct *vmg)
+{
+	const unsigned long size = vmg->end - vmg->start;
+
+	return size >> PAGE_SHIFT;
+}
+
+static inline pgoff_t vmg_end_pgoff(const struct vma_merge_struct *vmg)
+{
+	return vmg_start_pgoff(vmg) + vmg_pages(vmg);
+}
+
 /* Assumes addr >= vma->vm_start. */
 static inline pgoff_t vma_pgoff_offset(struct vm_area_struct *vma,
 				       unsigned long addr)