+ mm-vmalloc-extract-vm_area_free_pages-helper-from-vfree.patch added to mm-new branch

+ mm-vmalloc-extract-vm_area_free_pages-helper-from-vfree.patch added to mm-new branch

[Andrew Morton]

The patch titled
     Subject: mm/vmalloc: extract vm_area_free_pages() helper from vfree()
has been added to the -mm mm-new branch.  Its filename is
     mm-vmalloc-extract-vm_area_free_pages-helper-from-vfree.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-vmalloc-extract-vm_area_free_pages-helper-from-vfree.patch

This patch will later appear in the mm-new branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

Note, mm-new is a provisional staging ground for work-in-progress
patches, and acceptance into mm-new is a notification for others take
notice and to finish up reviews.  Please do not hesitate to respond to
review feedback and post updated versions to replace or incrementally
fixup patches in mm-new.

The mm-new branch of mm.git is not included in linux-next

If a few days of testing in mm-new is successful, the patch will me moved
into mm.git's mm-unstable branch, which is included in linux-next

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------------------------------------------------------
From: Shivam Kalra <shivamkalra98@zohomail.in>
Subject: mm/vmalloc: extract vm_area_free_pages() helper from vfree()
Date: Tue, 19 May 2026 17:42:14 +0530

Patch series "mm/vmalloc: free unused pages on vrealloc() shrink", v14.

This series implements the TODO in vrealloc() to unmap and free unused
pages when shrinking across a page boundary.

Problem:
When vrealloc() shrinks an allocation, it updates bookkeeping
(requested_size, KASAN shadow) but does not free the underlying physical
pages. This wastes memory for the lifetime of the allocation.

Solution:
- Patch 1: Extracts a vm_area_free_pages(vm, start_idx, end_idx) helper
  from vfree() that frees a range of pages with memcg and nr_vmalloc_pages
  accounting. Freed page pointers are set to NULL to prevent stale
  references.
- Patch 2: Update the grow-in-place check in vrealloc() to compare the
  requested size against the actual physical page count (vm->nr_pages) 
  rather than the virtual area sizes. This is a prerequisite for shrinking.
- Patch 3: For VM_ALLOC areas in vread_iter(), derive the vm area size 
  from vm->nr_pages rather than get_vm_area_size(), which would 
  overestimate the mapped range after a shrink. Other mapping types
  (vmap, ioremap) don't set nr_pages and keep using get_vm_area_size().
- Patch 4: Uses the helper to free tail pages when vrealloc() shrinks
  across a page boundary. 
- Patch 5: Adds a vrealloc test case to lib/test_vmalloc that exercises
  grow-realloc, shrink-across-boundary, shrink-within-page, and
  grow-in-place paths.

The virtual address reservation is kept intact to preserve the range for
potential future grow-in-place support.  A concrete user is the Rust
binder driver's KVVec::shrink_to [1], which performs explicit vrealloc()
shrinks for memory reclamation.


This patch (of 5):

Extract page freeing and NR_VMALLOC stat accounting from vfree() into a
reusable vm_area_free_pages() helper.  The helper operates on a range
[start_idx, end_idx) 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).

Link: https://lore.kernel.org/20260519-vmalloc-shrink-v14-0-70b96ee3e9c9@zohomail.in
Link: https://lore.kernel.org/20260519-vmalloc-shrink-v14-1-70b96ee3e9c9@zohomail.in
Link: https://lore.kernel.org/all/20260216-binder-shrink-vec-v3-v6-0-ece8e8593e53@zohomail.in/ [1]
Signed-off-by: Shivam Kalra <shivamkalra98@zohomail.in>
Reviewed-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Cc: Alice Ryhl <aliceryhl@google.com>
Cc: Danilo Krummrich <dakr@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/vmalloc.c |   34 +++++++++++++++++++++++++++-------
 1 file changed, 27 insertions(+), 7 deletions(-)

--- a/mm/vmalloc.c~mm-vmalloc-extract-vm_area_free_pages-helper-from-vfree
+++ a/mm/vmalloc.c
@@ -3416,6 +3416,32 @@ 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_idx: first page index to free (inclusive)
+ * @end_idx: last page index to free (exclusive)
+ *
+ * Free pages [start_idx, end_idx) 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_idx,
+			       unsigned int end_idx)
+{
+	unsigned int i;
+
+	if (!(vm->flags & VM_MAP_PUT_PAGES)) {
+		for (i = start_idx; i < end_idx; i++)
+			mod_lruvec_page_state(vm->pages[i], NR_VMALLOC, -1);
+	}
+	free_pages_bulk(vm->pages + start_idx, end_idx - start_idx);
+
+	for (i = start_idx; i < end_idx; i++)
+		vm->pages[i] = NULL;
+}
+
 /**
  * vfree - Release memory allocated by vmalloc()
  * @addr:  Memory base address
@@ -3436,7 +3462,6 @@ void vfree_atomic(const void *addr)
 void vfree(const void *addr)
 {
 	struct vm_struct *vm;
-	int i;
 
 	if (unlikely(in_interrupt())) {
 		vfree_atomic(addr);
@@ -3460,12 +3485,7 @@ void vfree(const void *addr)
 	if (unlikely(vm->flags & VM_FLUSH_RESET_PERMS))
 		vm_reset_perms(vm);
 
-	if (!(vm->flags & VM_MAP_PUT_PAGES)) {
-		for (i = 0; i < vm->nr_pages; i++)
-			mod_lruvec_page_state(vm->pages[i], NR_VMALLOC, -1);
-	}
-	free_pages_bulk(vm->pages, vm->nr_pages);
-
+	vm_area_free_pages(vm, 0, vm->nr_pages);
 	kvfree(vm->pages);
 	kfree(vm);
 }
_

Patches currently in -mm which might be from shivamkalra98@zohomail.in are

mm-vmalloc-extract-vm_area_free_pages-helper-from-vfree.patch
mm-vmalloc-use-physical-page-count-for-vrealloc-grow-in-place-check.patch
mm-vmalloc-use-physical-page-count-in-vread_iter-for-vm_alloc-areas.patch
mm-vmalloc-free-unused-pages-on-vrealloc-shrink.patch
lib-test_vmalloc-add-vrealloc-test-case.patch