[PATCH resend v6 00/30] mm/virtio: skip redundant zeroing of host-zeroed pages

[PATCH resend v6 00/30] mm/virtio: skip redundant zeroing of host-zeroed pages

[Michael S. Tsirkin]

Resending with no changes after a botched send. Fingers crossed.

When a guest reports free pages to the hypervisor via virtio-balloon's
free page reporting, the host typically zeros those pages when reclaiming
their backing memory (e.g., via MADV_DONTNEED on anonymous mappings).
When the guest later reallocates those pages, the kernel zeros them
again, redundantly.

Further, on architectures with aliasing caches, upstream with init_on_alloc
double-zeros user pages: once via kernel_init_pages() in
post_alloc_hook, and again via clear_user_highpage() at the
callsite (because user_alloc_needs_zeroing() returns true).
This series eliminates that double-zeroing by moving the zeroing
into the post_alloc_hook + propagating the "host
already zeroed this page" information through the buddy allocator.

For page reporting, VIRTIO_BALLOON_F_DEVICE_INIT_REPORTED (bit 6)
is used. For the inflate/deflate path,
VIRTIO_BALLOON_F_DEVICE_INIT_ON_INFLATE (bit 7) is used.

Virtio spec: https://lore.kernel.org/all/cover.1778140241.git.mst@redhat.com

Based on v7.1-rc2.  When applying on mm-unstable, two conflicts
are expected:
- kernel_init_pages() was renamed to clear_highpages_kasan_tagged()
  in mm-unstable.  Use clear_highpages_kasan_tagged() in the
  post_alloc_hook else branch.
- FPI_PREPARED uses BIT(3) in mm-unstable.  Bump FPI_ZEROED to
  BIT(4).
Build-tested on mm-unstable at e9dd96806dbc:
https://git.kernel.org/pub/scm/linux/kernel/git/mst/vhost.git zero-mm-unstable

The first 16 patches are independently mergeable cleanups + fixes:
- Patches 1-15: mm rework + cleanups + init_on_alloc double-zeroing fix.
- Patch 16: page_reporting capacity bugfix.
Patches 17-26: page reporting zeroing (DEVICE_INIT_REPORTED).
Patches 27-30: inflate/deflate zeroing (DEVICE_INIT_ON_INFLATE).

-------

Performance with THP enabled on a 2GB VM, 1 vCPU, allocating
256MB of anonymous pages:

  metric         baseline            optimized           delta
  task-clock     232 +- 20 ms        51 +- 26 ms         -78%
  cache-misses   1.20M +- 248K       288K +- 102K        -76%
  instructions   16.3M +- 1.2M       13.8M +- 1.0M       -15%

With hugetlb surplus pages:

  metric         baseline            optimized           delta
  task-clock     219 +- 23 ms        65 +- 34 ms         -70%
  cache-misses   1.17M +- 391K       263K +- 36K         -78%
  instructions   17.9M +- 1.2M       15.1M +- 724K       -16%

Two flags track known-zero pages:
  PG_zeroed (aliased to PG_private) marks buddy allocator pages that
  are known to contain all zeros -- either because the host zeroed
  them during page reporting, or because they were freed via the
  balloon deflate path.  It lives on free-list pages and is consumed
  by post_alloc_hook() on allocation.
  HPG_zeroed (stored in hugetlb folio->private bits) serves the same
  purpose for hugetlb pool pages, which are kept in a pool and may
  be zeroed long after buddy allocation, so PG_zeroed (consumed at
  allocation time) cannot track their state.

PG_zeroed lifecycle:

  Sets PG_zeroed:
  - page_reporting_drain: on reported pages when host zeroes them
  - __free_pages_ok / __free_frozen_pages: when FPI_ZEROED is set
    (balloon deflate path)
  - buddy merge: on merged page if both buddies were zeroed
  - expand(): propagate to split-off buddy sub-pages

  Clears PG_zeroed:
  - __free_pages_prepare: clears all PAGE_FLAGS_CHECK_AT_PREP flags
    (PG_zeroed included), preventing PG_private aliasing leaks
  - rmqueue_buddy / __rmqueue_pcplist: read-then-clear, passes
    zeroed hint to prep_new_page -> post_alloc_hook
  - __isolate_free_page: clear (compaction/page_reporting isolation)
  - compaction, alloc_contig, split_free_frozen: clear before use
  - buddy merge: clear both pages before merge, then conditionally
    re-set on merged head if both were zeroed

HPG_zeroed lifecycle (hugetlb pool pages, stored in folio->private):

  Sets HPG_zeroed:
  - alloc_surplus_hugetlb_folio: after buddy allocation with
    __GFP_ZERO, mark pool page as known-zero

  Clears HPG_zeroed:
  - free_huge_folio: page was mapped to userspace, no longer
    known-zero when it returns to the pool
  - alloc_hugetlb_folio / alloc_hugetlb_folio_reserve: clear
    after reporting to caller via bool *zeroed output (consumed)

- The optimization is most effective with THP, where entire 2MB
  pages are allocated directly from reported order-9+ buddy pages.
  Without THP, only ~21% of order-0 allocations come from reported
  pages due to low-order fragmentation.
- Persistent hugetlb pool pages are not covered: when freed by
  userspace they return to the hugetlb free pool, not the buddy
  allocator, so they are never reported to the host.  Surplus
  hugetlb pages are allocated from buddy and do benefit.

- PG_zeroed is aliased to PG_private.  __free_pages_prepare() clears it
  (preventing filesystem PG_private from leaking as false PG_zeroed).
  FPI_ZEROED re-sets it after prepare for balloon deflate pages.
  Is aliasing PG_private acceptable, or should a different bit be used?

- On architectures with aliasing caches, upstream with init_on_alloc
  double-zeros user pages: once via kernel_init_pages() in
  post_alloc_hook, and again via clear_user_highpage() at the
  callsite (because user_alloc_needs_zeroing() returns true).
  Our patches eliminate this by zeroing once via folio_zero_user()
  in post_alloc_hook.  Not a critical fix (people who set init_on_alloc
  know they are paying performance) but a nice cleanup anyway.


Test program:

  #include <stdio.h>
  #include <stdlib.h>
  #include <string.h>
  #include <sys/mman.h>

  #ifndef MADV_POPULATE_WRITE
  #define MADV_POPULATE_WRITE 23
  #endif
  #ifndef MAP_HUGETLB
  #define MAP_HUGETLB 0x40000
  #endif

  int main(int argc, char **argv)
  {
      unsigned long size;
      int flags = MAP_PRIVATE | MAP_ANONYMOUS;
      void *p;
      int r;

      if (argc < 2) {
          fprintf(stderr, "usage: %s <size_mb> [huge]\n", argv[0]);
          return 1;
      }
      size = atol(argv[1]) * 1024UL * 1024;
      if (argc >= 3 && strcmp(argv[2], "huge") == 0)
          flags |= MAP_HUGETLB;
      p = mmap(NULL, size, PROT_READ | PROT_WRITE, flags, -1, 0);
      if (p == MAP_FAILED) {
          perror("mmap");
          return 1;
      }
      r = madvise(p, size, MADV_POPULATE_WRITE);
      if (r) {
          perror("madvise");
          return 1;
      }
      munmap(p, size);
      return 0;
  }

Test script (bench.sh):

  #!/bin/bash
  # Usage: bench.sh <size_mb> <mode> <iterations> [huge]
  # mode 0 = baseline, mode 1 = skip zeroing
  SZ=${1:-256}; MODE=${2:-0}; ITER=${3:-10}; HUGE=${4:-}
  FLUSH=/sys/module/page_reporting/parameters/flush
  PERF_DATA=/tmp/perf-$MODE.csv
  rmmod virtio_balloon 2>/dev/null
  insmod virtio_balloon.ko host_zeroes_pages=$MODE
  echo 512 > $FLUSH
  [ "$HUGE" = "huge" ] && echo $((SZ/2)) > /proc/sys/vm/nr_overcommit_hugepages
  rm -f $PERF_DATA
  echo "=== sz=${SZ}MB mode=$MODE iter=$ITER $HUGE ==="
  for i in $(seq 1 $ITER); do
      echo 3 > /proc/sys/vm/drop_caches
      echo 512 > $FLUSH
      perf stat -e task-clock,instructions,cache-misses \
          -x, -o $PERF_DATA --append -- ./alloc_once $SZ $HUGE
  done
  [ "$HUGE" = "huge" ] && echo 0 > /proc/sys/vm/nr_overcommit_hugepages
  rmmod virtio_balloon
  awk -F, '/^#/||/^$/{next}{v=$1+0;e=$3;gsub(/ /,"",e);s[e]+=v;ss[e]+=v*v;n[e]++}
  END{for(e in s){a=s[e]/n[e];d=sqrt(ss[e]/n[e]-a*a);printf "  %-16s %10.0f +- %8.0f (n=%d)\n",e,a,d,n[e]}}' $PERF_DATA

Compile and run:
  gcc -static -O2 -o alloc_once alloc_once.c
  bash bench.sh 256 0 10          # baseline (regular pages)
  bash bench.sh 256 1 10          # optimized (regular pages)
  bash bench.sh 256 0 10 huge     # baseline (hugetlb surplus)
  bash bench.sh 256 1 10 huge     # optimized (hugetlb surplus)

Changes since v5:
- Rebased onto v7.1-rc2.
- Split alloc_anon_folio and alloc_swap_folio raw fault address
  changes into separate patches.
- In virtio, move PAGE_POISON check for DEVICE_INIT_REPORTED
  from probe() to validate(), clearing the feature instead of
  just gating host_zeroes_pages.  Same for confidential
  computing check.
- Fix bisectability: FPI_ZEROED definition and usage now in
  the same patch.
- Lots of commit log tweaks.
- Reorder: REPORTED before ON_INFLATE.
- Kerneldoc fixes.

Changes since v4:
With virtio spec posted, update to latest spec:
- Add VIRTIO_BALLOON_F_DEVICE_INIT_REPORTED (bit 6) for reporting.
- Add VIRTIO_BALLOON_F_DEVICE_INIT_ON_INFLATE (bit 7) for inflate.
- Per-page virtqueue submission, per-page used_len feedback.
- Balloon migration preserves PageZeroed hint.
- Page_reporting capacity bugfix for small virtqueues.
- PG_zeroed propagation in split_large_buddy.
- Disable both features for confidential computing guests.
- Gate host_zeroes_pages on PAGE_POISON/poison_val: when PAGE_POISON
  is negotiated with non-zero poison_val, device fills with poison
  not zeros, so host_zeroes_pages must be false.
- Disable ON_INFLATE when PAGE_POISON with non-zero poison_val.
- Bound inflate bitmap reads by used_len from device.
- Move ON_INFLATE poison_val check to validate() for proper
  feature negotiation.
- Fix NUMA interleave index for unaligned VMA start (new patch 1).
- Drop vma_alloc_folio_user_addr: with the ilx fix, callers can
  pass raw fault address to vma_alloc_folio directly.
- Tested with DEBUG_VM, INIT_ON_ALLOC/FREE enabled.

Changes since v3 (address review by Gregory Price and David Hildenbrand):
- Keep user_addr threading internal: public APIs (__alloc_pages,
  __folio_alloc, folio_alloc_mpol) are unchanged.  Only internal
  functions (__alloc_frozen_pages_noprof, __alloc_pages_mpol) carry
  user_addr.  This eliminates all API churn for external callers.
- Add vma_alloc_folio_user_addr() (2/22) to separate NUMA policy
  address from the zeroing hint address.  Fixes NUMA interleave
  index corruption when passing unaligned fault address for
  higher-order allocations.
- Add per-page zeroed_bitmap to page_reporting_dev_info (17/22).
  The driver's report() callback manages the bitmap.  Drain
  checks it gated by the host_zeroes_pages static key.  This
  matches the proposed virtio balloon extension at
  https://lore.kernel.org/all/cover.1776874126.git.mst@redhat.com/
- Clear PG_zeroed in __isolate_free_page() to prevent the aliased
  PG_private flag from leaking to compaction/alloc_contig paths.
- Do not exclude PG_zeroed from PAGE_FLAGS_CHECK_AT_PREP macro.
  Instead, __free_pages_prepare() clears it (preventing filesystem
  PG_private leaking as false PG_zeroed), and FPI_ZEROED sets it
  after prepare.  Only buddy merge assertion is relaxed.
- Initialize alloc_context.user_addr in alloc_pages_bulk_noprof.
- Deflate and hugetlb changes are much smaller now.  Still, the
  patchset can be merged gradually, if desired.

Changes since v2 (address review by Gregory Price and David Hildenbrand):
- v2 used pghint_t / vma_alloc_folio_hints API.  v3 switches to
  threading user_addr through the page allocator and using __GFP_ZERO,
  so post_alloc_hook() can use folio_zero_user() for cache-friendly
  zeroing when the user fault address is known.
- Use FPI_ZEROED to set PG_zeroed after __free_pages_prepare() instead
  of runtime masking in __free_one_page (further refined in v4).
- Drop redundant page_poisoning_enabled() check from mm core free
  path -- already guarded at feature negotiation time in
  virtio_balloon_validate.  The balloon driver keeps its own
  page_poisoning_enabled_static() check as defense in depth.
- Split free_frozen_pages_zeroed and put_page_zeroed into separate
  patches.  David Hildenbrand indicated he intends to rework balloon
  pages to be frozen (no refcount), at which point put_page_zeroed
  (21/22) can be dropped and the balloon can call
  free_frozen_pages_zeroed directly.
- Use HPG_zeroed flag (in hugetlb folio->private) for hugetlb pool
  pages instead of PG_zeroed, since pool pages are zeroed long after
  buddy allocation and PG_zeroed is consumed at allocation time.
- syzbot CI found a PF_NO_COMPOUND BUG in the v2 pghint_t approach
  where __ClearPageZeroed was called on compound hugetlb pages in
  free_huge_folio.  The v3 HPG_zeroed approach avoids this.
- Remove redundant arch vma_alloc_zeroed_movable_folio overrides
  on x86, s390, m68k, and alpha (12/22). Suggested by David
  Hildenbrand.
- Updated benchmarking script to compute per-run avg +- stddev
  via awk on CSV output.

Changes v1->v2:
- Replaced __GFP_PREZEROED with PG_zeroed page flag (aliased PG_private)
- Added pghint_t type and vma_alloc_folio_hints() API
- Track PG_zeroed across buddy merges and splits
- Added post_alloc_hook integration (single consume/clear point)
- Added hugetlb support (pool pages + memfd)
- Added page_reporting flush parameter for deterministic testing
- Added free_frozen_pages_hint/put_page_hint for balloon deflate path
- Added try_to_claim_block PG_zeroed preservation
- Updated perf numbers with per-iteration flush methodology

Written with assistance from Claude (claude-opus-4-6).
Reviewed by cursor-agent (GPT-5.4-xhigh).
Everything manually read, patchset split and commit logs edited manually.

Michael S. Tsirkin (30):
  mm: move vma_alloc_folio_noprof to page_alloc.c
  mm: mempolicy: fix interleave index for unaligned VMA start
  mm: thread user_addr through page allocator for cache-friendly zeroing
  mm: add folio_zero_user stub for configs without THP/HUGETLBFS
  mm: page_alloc: move prep_compound_page before post_alloc_hook
  mm: use folio_zero_user for user pages in post_alloc_hook
  mm: use __GFP_ZERO in vma_alloc_zeroed_movable_folio
  mm: remove arch vma_alloc_zeroed_movable_folio overrides
  mm: alloc_anon_folio: pass raw fault address to vma_alloc_folio
  mm: alloc_swap_folio: pass raw fault address to vma_alloc_folio
  mm: use __GFP_ZERO in alloc_anon_folio
  mm: vma_alloc_anon_folio_pmd: pass raw fault address to
    vma_alloc_folio
  mm: use __GFP_ZERO in vma_alloc_anon_folio_pmd
  mm: hugetlb: use __GFP_ZERO and skip zeroing for zeroed pages
  mm: memfd: skip zeroing for zeroed hugetlb pool pages
  mm: page_reporting: allow driver to set batch capacity
  mm: page_alloc: propagate PageReported flag across buddy splits
  mm: page_reporting: skip redundant zeroing of host-zeroed reported
    pages
  mm: page_reporting: add per-page zeroed bitmap for host feedback
  mm: page_alloc: clear PG_zeroed on buddy merge if not both zero
  mm: page_alloc: preserve PG_zeroed in page_del_and_expand
  virtio_balloon: submit reported pages as individual buffers
  mm: page_reporting: add flush parameter with page budget
  mm: page_alloc: propagate PG_zeroed in split_large_buddy
  virtio_balloon: skip zeroing for host-zeroed reported pages
  virtio_balloon: disable reporting zeroed optimization for confidential
    guests
  mm: add free_frozen_pages_zeroed
  mm: add put_page_zeroed and folio_put_zeroed
  virtio_balloon: implement VIRTIO_BALLOON_F_DEVICE_INIT_ON_INFLATE
  mm: balloon: use put_page_zeroed for zeroed balloon pages

 arch/alpha/include/asm/page.h       |   3 -
 arch/m68k/include/asm/page_no.h     |   3 -
 arch/s390/include/asm/page.h        |   3 -
 arch/x86/include/asm/page.h         |   3 -
 drivers/virtio/virtio_balloon.c     | 160 +++++++++++++++++----
 fs/hugetlbfs/inode.c                |  10 +-
 include/linux/gfp.h                 |  12 +-
 include/linux/highmem.h             |   9 +-
 include/linux/hugetlb.h             |  14 +-
 include/linux/mm.h                  |  15 ++
 include/linux/page-flags.h          |   9 ++
 include/linux/page_reporting.h      |  13 ++
 include/uapi/linux/virtio_balloon.h |   2 +
 mm/balloon.c                        |   7 +-
 mm/compaction.c                     |   7 +-
 mm/huge_memory.c                    |  12 +-
 mm/hugetlb.c                        |  99 +++++++++----
 mm/internal.h                       |  17 ++-
 mm/memfd.c                          |  14 +-
 mm/memory.c                         |  17 +--
 mm/mempolicy.c                      |  73 ++++------
 mm/page_alloc.c                     | 213 +++++++++++++++++++++++-----
 mm/page_reporting.c                 |  88 ++++++++++--
 mm/page_reporting.h                 |  12 ++
 mm/slub.c                           |   4 +-
 mm/swap.c                           |  18 ++-
 26 files changed, 615 insertions(+), 222 deletions(-)

-- 
MST

[PATCH resend v6 01/30] mm: move vma_alloc_folio_noprof to page_alloc.c

[Michael S. Tsirkin]

Move vma_alloc_folio_noprof() from an inline in gfp.h (for !NUMA)
and mempolicy.c (for NUMA) to page_alloc.c.

This prepares for a subsequent patch that will thread user_addr
through the allocator: having vma_alloc_folio_noprof in page_alloc.c
means user_addr can be passed to the internal allocation path
without changing public API signatures or duplicating plumbing
in both gfp.h and mempolicy.c.

The !NUMA path gains the VM_DROPPABLE -> __GFP_NOWARN check
that the NUMA path already had.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Assisted-by: Claude:claude-opus-4-6
Assisted-by: cursor-agent:GPT-5.4-xhigh
---
 include/linux/gfp.h |  9 ++-------
 mm/mempolicy.c      | 32 --------------------------------
 mm/page_alloc.c     | 43 +++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 45 insertions(+), 39 deletions(-)

diff --git a/include/linux/gfp.h b/include/linux/gfp.h
index 51ef13ed756e..7ccbda35b9ad 100644
--- a/include/linux/gfp.h
+++ b/include/linux/gfp.h
@@ -318,13 +318,13 @@ static inline struct page *alloc_pages_node_noprof(int nid, gfp_t gfp_mask,
 
 #define  alloc_pages_node(...)			alloc_hooks(alloc_pages_node_noprof(__VA_ARGS__))
 
+struct folio *vma_alloc_folio_noprof(gfp_t gfp, int order,
+		struct vm_area_struct *vma, unsigned long addr);
 #ifdef CONFIG_NUMA
 struct page *alloc_pages_noprof(gfp_t gfp, unsigned int order);
 struct folio *folio_alloc_noprof(gfp_t gfp, unsigned int order);
 struct folio *folio_alloc_mpol_noprof(gfp_t gfp, unsigned int order,
 		struct mempolicy *mpol, pgoff_t ilx, int nid);
-struct folio *vma_alloc_folio_noprof(gfp_t gfp, int order, struct vm_area_struct *vma,
-		unsigned long addr);
 #else
 static inline struct page *alloc_pages_noprof(gfp_t gfp_mask, unsigned int order)
 {
@@ -339,11 +339,6 @@ static inline struct folio *folio_alloc_mpol_noprof(gfp_t gfp, unsigned int orde
 {
 	return folio_alloc_noprof(gfp, order);
 }
-static inline struct folio *vma_alloc_folio_noprof(gfp_t gfp, int order,
-		struct vm_area_struct *vma, unsigned long addr)
-{
-	return folio_alloc_noprof(gfp, order);
-}
 #endif
 
 #define alloc_pages(...)			alloc_hooks(alloc_pages_noprof(__VA_ARGS__))
diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 4e4421b22b59..6832cc68120f 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -2515,38 +2515,6 @@ struct folio *folio_alloc_mpol_noprof(gfp_t gfp, unsigned int order,
 	return page_rmappable_folio(page);
 }
 
-/**
- * vma_alloc_folio - Allocate a folio for a VMA.
- * @gfp: GFP flags.
- * @order: Order of the folio.
- * @vma: Pointer to VMA.
- * @addr: Virtual address of the allocation.  Must be inside @vma.
- *
- * Allocate a folio for a specific address in @vma, using the appropriate
- * NUMA policy.  The caller must hold the mmap_lock of the mm_struct of the
- * VMA to prevent it from going away.  Should be used for all allocations
- * for folios that will be mapped into user space, excepting hugetlbfs, and
- * excepting where direct use of folio_alloc_mpol() is more appropriate.
- *
- * Return: The folio on success or NULL if allocation fails.
- */
-struct folio *vma_alloc_folio_noprof(gfp_t gfp, int order, struct vm_area_struct *vma,
-		unsigned long addr)
-{
-	struct mempolicy *pol;
-	pgoff_t ilx;
-	struct folio *folio;
-
-	if (vma->vm_flags & VM_DROPPABLE)
-		gfp |= __GFP_NOWARN;
-
-	pol = get_vma_policy(vma, addr, order, &ilx);
-	folio = folio_alloc_mpol_noprof(gfp, order, pol, ilx, numa_node_id());
-	mpol_cond_put(pol);
-	return folio;
-}
-EXPORT_SYMBOL(vma_alloc_folio_noprof);
-
 struct page *alloc_frozen_pages_noprof(gfp_t gfp, unsigned order)
 {
 	struct mempolicy *pol = &default_policy;
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 227d58dc3de6..fc7327ebdf6c 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -5273,6 +5273,49 @@ struct folio *__folio_alloc_noprof(gfp_t gfp, unsigned int order, int preferred_
 }
 EXPORT_SYMBOL(__folio_alloc_noprof);
 
+#ifdef CONFIG_NUMA
+/**
+ * vma_alloc_folio - Allocate a folio for a VMA.
+ * @gfp: GFP flags.
+ * @order: Order of the folio.
+ * @vma: Pointer to VMA.
+ * @addr: Virtual address of the allocation.  Must be inside @vma.
+ *
+ * Allocate a folio for a specific address in @vma, using the appropriate
+ * NUMA policy.  The caller must hold the mmap_lock of the mm_struct of the
+ * VMA to prevent it from going away.  Should be used for all allocations
+ * for folios that will be mapped into user space, excepting hugetlbfs, and
+ * excepting where direct use of folio_alloc_mpol() is more appropriate.
+ *
+ * Return: The folio on success or NULL if allocation fails.
+ */
+struct folio *vma_alloc_folio_noprof(gfp_t gfp, int order,
+		struct vm_area_struct *vma, unsigned long addr)
+{
+	struct mempolicy *pol;
+	pgoff_t ilx;
+	struct folio *folio;
+
+	if (vma->vm_flags & VM_DROPPABLE)
+		gfp |= __GFP_NOWARN;
+
+	pol = get_vma_policy(vma, addr, order, &ilx);
+	folio = folio_alloc_mpol_noprof(gfp, order, pol, ilx, numa_node_id());
+	mpol_cond_put(pol);
+	return folio;
+}
+#else
+struct folio *vma_alloc_folio_noprof(gfp_t gfp, int order,
+		struct vm_area_struct *vma, unsigned long addr)
+{
+	if (vma->vm_flags & VM_DROPPABLE)
+		gfp |= __GFP_NOWARN;
+
+	return folio_alloc_noprof(gfp, order);
+}
+#endif
+EXPORT_SYMBOL(vma_alloc_folio_noprof);
+
 /*
  * Common helper functions. Never use with __GFP_HIGHMEM because the returned
  * address cannot represent highmem pages. Use alloc_pages and then kmap if
-- 
MST

[PATCH resend v6 02/30] mm: mempolicy: fix interleave index for unaligned VMA start

[Michael S. Tsirkin]

The NUMA interleave index formula (addr - vm_start) >> shift
gives wrong results when vm_start is not aligned to the folio
size: the subtraction before the shift allows low bits to
affect the result via borrows.

Use (addr >> shift) - (vm_start >> shift) instead, which
independently aligns both values before computing the
difference.

No functional change for current callers: the fix only affects
NUMA interleave and weighted-interleave policies. Current
large-order callers either pre-align the address
(vma_alloc_anon_folio_pmd) or do not use NUMA interleave
(drm_pagemap). All other callers use order 0 where the old
and new formulas are equivalent. However subsequent patches
in this series add large-order callers that pass unaligned
fault addresses, making this fix necessary.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---
 mm/mempolicy.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 6832cc68120f..39e556e3d263 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -2049,7 +2049,8 @@ struct mempolicy *get_vma_policy(struct vm_area_struct *vma,
 	if (pol->mode == MPOL_INTERLEAVE ||
 	    pol->mode == MPOL_WEIGHTED_INTERLEAVE) {
 		*ilx += vma->vm_pgoff >> order;
-		*ilx += (addr - vma->vm_start) >> (PAGE_SHIFT + order);
+		*ilx += (addr >> (PAGE_SHIFT + order)) -
+			(vma->vm_start >> (PAGE_SHIFT + order));
 	}
 	return pol;
 }
-- 
MST

[PATCH resend v6 03/30] mm: thread user_addr through page allocator for cache-friendly zeroing

[Michael S. Tsirkin]

Thread a user virtual address from vma_alloc_folio() down through
the page allocator to post_alloc_hook(). This is plumbing
preparation for a subsequent patch that will use user_addr to
call folio_zero_user() for cache-friendly zeroing of user pages.

The user_addr is stored in struct alloc_context and flows through:
  vma_alloc_folio -> folio_alloc_mpol -> __alloc_pages_mpol ->
  __alloc_frozen_pages -> get_page_from_freelist -> prep_new_page ->
  post_alloc_hook

USER_ADDR_NONE ((unsigned long)-1) is used for non-user
allocations, since address 0 is a valid userspace mapping.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Assisted-by: Claude:claude-opus-4-6
Assisted-by: cursor-agent:GPT-5.4-xhigh
---
 include/linux/gfp.h |  2 +-
 mm/compaction.c     |  5 ++---
 mm/hugetlb.c        | 36 ++++++++++++++++++++----------------
 mm/internal.h       | 18 +++++++++++++++---
 mm/mempolicy.c      | 44 ++++++++++++++++++++++++++++++++------------
 mm/page_alloc.c     | 44 +++++++++++++++++++++++++++++---------------
 mm/slub.c           |  4 ++--
 7 files changed, 101 insertions(+), 52 deletions(-)

diff --git a/include/linux/gfp.h b/include/linux/gfp.h
index 7ccbda35b9ad..ee35c5367abc 100644
--- a/include/linux/gfp.h
+++ b/include/linux/gfp.h
@@ -337,7 +337,7 @@ static inline struct folio *folio_alloc_noprof(gfp_t gfp, unsigned int order)
 static inline struct folio *folio_alloc_mpol_noprof(gfp_t gfp, unsigned int order,
 		struct mempolicy *mpol, pgoff_t ilx, int nid)
 {
-	return folio_alloc_noprof(gfp, order);
+	return __folio_alloc_noprof(gfp, order, numa_node_id(), NULL);
 }
 #endif
 
diff --git a/mm/compaction.c b/mm/compaction.c
index 3648ce22c807..72684fe81e83 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -82,7 +82,7 @@ static inline bool is_via_compact_memory(int order) { return false; }
 
 static struct page *mark_allocated_noprof(struct page *page, unsigned int order, gfp_t gfp_flags)
 {
-	post_alloc_hook(page, order, __GFP_MOVABLE);
+	post_alloc_hook(page, order, __GFP_MOVABLE, USER_ADDR_NONE);
 	set_page_refcounted(page);
 	return page;
 }
@@ -1849,8 +1849,7 @@ static struct folio *compaction_alloc_noprof(struct folio *src, unsigned long da
 		set_page_private(&freepage[size], start_order);
 	}
 	dst = (struct folio *)freepage;
-
-	post_alloc_hook(&dst->page, order, __GFP_MOVABLE);
+	post_alloc_hook(&dst->page, order, __GFP_MOVABLE, USER_ADDR_NONE);
 	set_page_refcounted(&dst->page);
 	if (order)
 		prep_compound_page(&dst->page, order);
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index f24bf49be047..a999f3ead852 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -1806,7 +1806,8 @@ struct address_space *hugetlb_folio_mapping_lock_write(struct folio *folio)
 }
 
 static struct folio *alloc_buddy_frozen_folio(int order, gfp_t gfp_mask,
-		int nid, nodemask_t *nmask, nodemask_t *node_alloc_noretry)
+		int nid, nodemask_t *nmask, nodemask_t *node_alloc_noretry,
+		unsigned long addr)
 {
 	struct folio *folio;
 	bool alloc_try_hard = true;
@@ -1823,7 +1824,7 @@ static struct folio *alloc_buddy_frozen_folio(int order, gfp_t gfp_mask,
 	if (alloc_try_hard)
 		gfp_mask |= __GFP_RETRY_MAYFAIL;
 
-	folio = (struct folio *)__alloc_frozen_pages(gfp_mask, order, nid, nmask);
+	folio = (struct folio *)__alloc_frozen_pages(gfp_mask, order, nid, nmask, addr);
 
 	/*
 	 * If we did not specify __GFP_RETRY_MAYFAIL, but still got a
@@ -1852,7 +1853,7 @@ static struct folio *alloc_buddy_frozen_folio(int order, gfp_t gfp_mask,
 
 static struct folio *only_alloc_fresh_hugetlb_folio(struct hstate *h,
 		gfp_t gfp_mask, int nid, nodemask_t *nmask,
-		nodemask_t *node_alloc_noretry)
+		nodemask_t *node_alloc_noretry, unsigned long addr)
 {
 	struct folio *folio;
 	int order = huge_page_order(h);
@@ -1864,7 +1865,7 @@ static struct folio *only_alloc_fresh_hugetlb_folio(struct hstate *h,
 		folio = alloc_gigantic_frozen_folio(order, gfp_mask, nid, nmask);
 	else
 		folio = alloc_buddy_frozen_folio(order, gfp_mask, nid, nmask,
-						 node_alloc_noretry);
+						 node_alloc_noretry, addr);
 	if (folio)
 		init_new_hugetlb_folio(folio);
 	return folio;
@@ -1878,11 +1879,12 @@ static struct folio *only_alloc_fresh_hugetlb_folio(struct hstate *h,
  * pages is zero, and the accounting must be done in the caller.
  */
 static struct folio *alloc_fresh_hugetlb_folio(struct hstate *h,
-		gfp_t gfp_mask, int nid, nodemask_t *nmask)
+		gfp_t gfp_mask, int nid, nodemask_t *nmask,
+		unsigned long addr)
 {
 	struct folio *folio;
 
-	folio = only_alloc_fresh_hugetlb_folio(h, gfp_mask, nid, nmask, NULL);
+	folio = only_alloc_fresh_hugetlb_folio(h, gfp_mask, nid, nmask, NULL, addr);
 	if (folio)
 		hugetlb_vmemmap_optimize_folio(h, folio);
 	return folio;
@@ -1922,7 +1924,7 @@ static struct folio *alloc_pool_huge_folio(struct hstate *h,
 		struct folio *folio;
 
 		folio = only_alloc_fresh_hugetlb_folio(h, gfp_mask, node,
-					nodes_allowed, node_alloc_noretry);
+					nodes_allowed, node_alloc_noretry, USER_ADDR_NONE);
 		if (folio)
 			return folio;
 	}
@@ -2091,7 +2093,8 @@ int dissolve_free_hugetlb_folios(unsigned long start_pfn, unsigned long end_pfn)
  * Allocates a fresh surplus page from the page allocator.
  */
 static struct folio *alloc_surplus_hugetlb_folio(struct hstate *h,
-				gfp_t gfp_mask,	int nid, nodemask_t *nmask)
+				gfp_t gfp_mask,	int nid, nodemask_t *nmask,
+				unsigned long addr)
 {
 	struct folio *folio = NULL;
 
@@ -2103,7 +2106,7 @@ static struct folio *alloc_surplus_hugetlb_folio(struct hstate *h,
 		goto out_unlock;
 	spin_unlock_irq(&hugetlb_lock);
 
-	folio = alloc_fresh_hugetlb_folio(h, gfp_mask, nid, nmask);
+	folio = alloc_fresh_hugetlb_folio(h, gfp_mask, nid, nmask, addr);
 	if (!folio)
 		return NULL;
 
@@ -2146,7 +2149,7 @@ static struct folio *alloc_migrate_hugetlb_folio(struct hstate *h, gfp_t gfp_mas
 	if (hstate_is_gigantic(h))
 		return NULL;
 
-	folio = alloc_fresh_hugetlb_folio(h, gfp_mask, nid, nmask);
+	folio = alloc_fresh_hugetlb_folio(h, gfp_mask, nid, nmask, USER_ADDR_NONE);
 	if (!folio)
 		return NULL;
 
@@ -2182,14 +2185,14 @@ struct folio *alloc_buddy_hugetlb_folio_with_mpol(struct hstate *h,
 	if (mpol_is_preferred_many(mpol)) {
 		gfp_t gfp = gfp_mask & ~(__GFP_DIRECT_RECLAIM | __GFP_NOFAIL);
 
-		folio = alloc_surplus_hugetlb_folio(h, gfp, nid, nodemask);
+		folio = alloc_surplus_hugetlb_folio(h, gfp, nid, nodemask, addr);
 
 		/* Fallback to all nodes if page==NULL */
 		nodemask = NULL;
 	}
 
 	if (!folio)
-		folio = alloc_surplus_hugetlb_folio(h, gfp_mask, nid, nodemask);
+		folio = alloc_surplus_hugetlb_folio(h, gfp_mask, nid, nodemask, addr);
 	mpol_cond_put(mpol);
 	return folio;
 }
@@ -2296,7 +2299,8 @@ static int gather_surplus_pages(struct hstate *h, long delta)
 		 * down the road to pick the current node if that is the case.
 		 */
 		folio = alloc_surplus_hugetlb_folio(h, htlb_alloc_mask(h),
-						    NUMA_NO_NODE, &alloc_nodemask);
+						    NUMA_NO_NODE, &alloc_nodemask,
+						    USER_ADDR_NONE);
 		if (!folio) {
 			alloc_ok = false;
 			break;
@@ -2702,7 +2706,7 @@ static int alloc_and_dissolve_hugetlb_folio(struct folio *old_folio,
 			spin_unlock_irq(&hugetlb_lock);
 			gfp_mask = htlb_alloc_mask(h) | __GFP_THISNODE;
 			new_folio = alloc_fresh_hugetlb_folio(h, gfp_mask,
-							      nid, NULL);
+							      nid, NULL, USER_ADDR_NONE);
 			if (!new_folio)
 				return -ENOMEM;
 			goto retry;
@@ -3400,13 +3404,13 @@ static void __init hugetlb_hstate_alloc_pages_onenode(struct hstate *h, int nid)
 			gfp_t gfp_mask = htlb_alloc_mask(h) | __GFP_THISNODE;
 
 			folio = only_alloc_fresh_hugetlb_folio(h, gfp_mask, nid,
-					&node_states[N_MEMORY], NULL);
+					&node_states[N_MEMORY], NULL, USER_ADDR_NONE);
 			if (!folio && !list_empty(&folio_list) &&
 			    hugetlb_vmemmap_optimizable_size(h)) {
 				prep_and_add_allocated_folios(h, &folio_list);
 				INIT_LIST_HEAD(&folio_list);
 				folio = only_alloc_fresh_hugetlb_folio(h, gfp_mask, nid,
-						&node_states[N_MEMORY], NULL);
+						&node_states[N_MEMORY], NULL, USER_ADDR_NONE);
 			}
 			if (!folio)
 				break;
diff --git a/mm/internal.h b/mm/internal.h
index 5a2ddcf68e0b..751ae8911607 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -662,6 +662,12 @@ void calculate_min_free_kbytes(void);
 int __meminit init_per_zone_wmark_min(void);
 void page_alloc_sysctl_init(void);
 
+/*
+ * Sentinel for user_addr: indicates a non-user allocation.
+ * Cannot use 0 because address 0 is a valid userspace mapping.
+ */
+#define USER_ADDR_NONE	((unsigned long)-1)
+
 /*
  * Structure for holding the mostly immutable allocation parameters passed
  * between functions involved in allocations, including the alloc_pages*
@@ -693,6 +699,7 @@ struct alloc_context {
 	 */
 	enum zone_type highest_zoneidx;
 	bool spread_dirty_pages;
+	unsigned long user_addr;
 };
 
 /*
@@ -916,24 +923,29 @@ static inline void init_compound_tail(struct page *tail,
 	prep_compound_tail(tail, head, order);
 }
 
-void post_alloc_hook(struct page *page, unsigned int order, gfp_t gfp_flags);
+void post_alloc_hook(struct page *page, unsigned int order, gfp_t gfp_flags,
+		     unsigned long user_addr);
 extern bool free_pages_prepare(struct page *page, unsigned int order);
 
 extern int user_min_free_kbytes;
 
 struct page *__alloc_frozen_pages_noprof(gfp_t, unsigned int order, int nid,
-		nodemask_t *);
+		nodemask_t *, unsigned long user_addr);
 #define __alloc_frozen_pages(...) \
 	alloc_hooks(__alloc_frozen_pages_noprof(__VA_ARGS__))
 void free_frozen_pages(struct page *page, unsigned int order);
+void free_frozen_pages_zeroed(struct page *page, unsigned int order);
 void free_unref_folios(struct folio_batch *fbatch);
 
 #ifdef CONFIG_NUMA
 struct page *alloc_frozen_pages_noprof(gfp_t, unsigned int order);
+struct folio *folio_alloc_mpol_user_noprof(gfp_t gfp, unsigned int order,
+		struct mempolicy *pol, pgoff_t ilx, int nid,
+		unsigned long user_addr);
 #else
 static inline struct page *alloc_frozen_pages_noprof(gfp_t gfp, unsigned int order)
 {
-	return __alloc_frozen_pages_noprof(gfp, order, numa_node_id(), NULL);
+	return __alloc_frozen_pages_noprof(gfp, order, numa_node_id(), NULL, USER_ADDR_NONE);
 }
 #endif
 
diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 39e556e3d263..ea3043e0075b 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -2413,7 +2413,8 @@ bool mempolicy_in_oom_domain(struct task_struct *tsk,
 }
 
 static struct page *alloc_pages_preferred_many(gfp_t gfp, unsigned int order,
-						int nid, nodemask_t *nodemask)
+						int nid, nodemask_t *nodemask,
+						unsigned long user_addr)
 {
 	struct page *page;
 	gfp_t preferred_gfp;
@@ -2426,25 +2427,29 @@ static struct page *alloc_pages_preferred_many(gfp_t gfp, unsigned int order,
 	 */
 	preferred_gfp = gfp | __GFP_NOWARN;
 	preferred_gfp &= ~(__GFP_DIRECT_RECLAIM | __GFP_NOFAIL);
-	page = __alloc_frozen_pages_noprof(preferred_gfp, order, nid, nodemask);
+	page = __alloc_frozen_pages_noprof(preferred_gfp, order, nid,
+					   nodemask, user_addr);
 	if (!page)
-		page = __alloc_frozen_pages_noprof(gfp, order, nid, NULL);
+		page = __alloc_frozen_pages_noprof(gfp, order, nid, NULL,
+						   user_addr);
 
 	return page;
 }
 
 /**
- * alloc_pages_mpol - Allocate pages according to NUMA mempolicy.
+ * __alloc_pages_mpol - Allocate pages according to NUMA mempolicy.
  * @gfp: GFP flags.
  * @order: Order of the page allocation.
  * @pol: Pointer to the NUMA mempolicy.
  * @ilx: Index for interleave mempolicy (also distinguishes alloc_pages()).
  * @nid: Preferred node (usually numa_node_id() but @mpol may override it).
+ * @user_addr: User fault address for cache-friendly zeroing, or USER_ADDR_NONE.
  *
  * Return: The page on success or NULL if allocation fails.
  */
-static struct page *alloc_pages_mpol(gfp_t gfp, unsigned int order,
-		struct mempolicy *pol, pgoff_t ilx, int nid)
+static struct page *__alloc_pages_mpol(gfp_t gfp, unsigned int order,
+		struct mempolicy *pol, pgoff_t ilx, int nid,
+		unsigned long user_addr)
 {
 	nodemask_t *nodemask;
 	struct page *page;
@@ -2452,7 +2457,8 @@ static struct page *alloc_pages_mpol(gfp_t gfp, unsigned int order,
 	nodemask = policy_nodemask(gfp, pol, ilx, &nid);
 
 	if (pol->mode == MPOL_PREFERRED_MANY)
-		return alloc_pages_preferred_many(gfp, order, nid, nodemask);
+		return alloc_pages_preferred_many(gfp, order, nid, nodemask,
+						 user_addr);
 
 	if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE) &&
 	    /* filter "hugepage" allocation, unless from alloc_pages() */
@@ -2476,7 +2482,7 @@ static struct page *alloc_pages_mpol(gfp_t gfp, unsigned int order,
 			 */
 			page = __alloc_frozen_pages_noprof(
 				gfp | __GFP_THISNODE | __GFP_NORETRY, order,
-				nid, NULL);
+				nid, NULL, user_addr);
 			if (page || !(gfp & __GFP_DIRECT_RECLAIM))
 				return page;
 			/*
@@ -2488,7 +2494,7 @@ static struct page *alloc_pages_mpol(gfp_t gfp, unsigned int order,
 		}
 	}
 
-	page = __alloc_frozen_pages_noprof(gfp, order, nid, nodemask);
+	page = __alloc_frozen_pages_noprof(gfp, order, nid, nodemask, user_addr);
 
 	if (unlikely(pol->mode == MPOL_INTERLEAVE ||
 		     pol->mode == MPOL_WEIGHTED_INTERLEAVE) && page) {
@@ -2504,11 +2510,18 @@ static struct page *alloc_pages_mpol(gfp_t gfp, unsigned int order,
 	return page;
 }
 
-struct folio *folio_alloc_mpol_noprof(gfp_t gfp, unsigned int order,
+static struct page *alloc_pages_mpol(gfp_t gfp, unsigned int order,
 		struct mempolicy *pol, pgoff_t ilx, int nid)
 {
-	struct page *page = alloc_pages_mpol(gfp | __GFP_COMP, order, pol,
-			ilx, nid);
+	return __alloc_pages_mpol(gfp, order, pol, ilx, nid, USER_ADDR_NONE);
+}
+
+struct folio *folio_alloc_mpol_user_noprof(gfp_t gfp, unsigned int order,
+		struct mempolicy *pol, pgoff_t ilx, int nid,
+		unsigned long user_addr)
+{
+	struct page *page = __alloc_pages_mpol(gfp | __GFP_COMP, order, pol,
+			ilx, nid, user_addr);
 	if (!page)
 		return NULL;
 
@@ -2516,6 +2529,13 @@ struct folio *folio_alloc_mpol_noprof(gfp_t gfp, unsigned int order,
 	return page_rmappable_folio(page);
 }
 
+struct folio *folio_alloc_mpol_noprof(gfp_t gfp, unsigned int order,
+		struct mempolicy *pol, pgoff_t ilx, int nid)
+{
+	return folio_alloc_mpol_user_noprof(gfp, order, pol, ilx, nid,
+					    USER_ADDR_NONE);
+}
+
 struct page *alloc_frozen_pages_noprof(gfp_t gfp, unsigned order)
 {
 	struct mempolicy *pol = &default_policy;
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index fc7327ebdf6c..c3c0f4e2baa7 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1806,7 +1806,7 @@ static inline bool should_skip_init(gfp_t flags)
 }
 
 inline void post_alloc_hook(struct page *page, unsigned int order,
-				gfp_t gfp_flags)
+				gfp_t gfp_flags, unsigned long user_addr)
 {
 	bool init = !want_init_on_free() && want_init_on_alloc(gfp_flags) &&
 			!should_skip_init(gfp_flags);
@@ -1861,9 +1861,10 @@ inline void post_alloc_hook(struct page *page, unsigned int order,
 }
 
 static void prep_new_page(struct page *page, unsigned int order, gfp_t gfp_flags,
-							unsigned int alloc_flags)
+							unsigned int alloc_flags,
+							unsigned long user_addr)
 {
-	post_alloc_hook(page, order, gfp_flags);
+	post_alloc_hook(page, order, gfp_flags, user_addr);
 
 	if (order && (gfp_flags & __GFP_COMP))
 		prep_compound_page(page, order);
@@ -3943,7 +3944,8 @@ get_page_from_freelist(gfp_t gfp_mask, unsigned int order, int alloc_flags,
 		page = rmqueue(zonelist_zone(ac->preferred_zoneref), zone, order,
 				gfp_mask, alloc_flags, ac->migratetype);
 		if (page) {
-			prep_new_page(page, order, gfp_mask, alloc_flags);
+			prep_new_page(page, order, gfp_mask, alloc_flags,
+				      ac->user_addr);
 
 			return page;
 		} else {
@@ -4171,7 +4173,8 @@ __alloc_pages_direct_compact(gfp_t gfp_mask, unsigned int order,
 
 	/* Prep a captured page if available */
 	if (page)
-		prep_new_page(page, order, gfp_mask, alloc_flags);
+		prep_new_page(page, order, gfp_mask, alloc_flags,
+			      ac->user_addr);
 
 	/* Try get a page from the freelist if available */
 	if (!page)
@@ -5048,7 +5051,7 @@ unsigned long alloc_pages_bulk_noprof(gfp_t gfp, int preferred_nid,
 	struct zoneref *z;
 	struct per_cpu_pages *pcp;
 	struct list_head *pcp_list;
-	struct alloc_context ac;
+	struct alloc_context ac = { .user_addr = USER_ADDR_NONE };
 	gfp_t alloc_gfp;
 	unsigned int alloc_flags = ALLOC_WMARK_LOW;
 	int nr_populated = 0, nr_account = 0;
@@ -5163,7 +5166,7 @@ unsigned long alloc_pages_bulk_noprof(gfp_t gfp, int preferred_nid,
 		}
 		nr_account++;
 
-		prep_new_page(page, 0, gfp, 0);
+		prep_new_page(page, 0, gfp, 0, USER_ADDR_NONE);
 		set_page_refcounted(page);
 		page_array[nr_populated++] = page;
 	}
@@ -5188,12 +5191,13 @@ EXPORT_SYMBOL_GPL(alloc_pages_bulk_noprof);
  * This is the 'heart' of the zoned buddy allocator.
  */
 struct page *__alloc_frozen_pages_noprof(gfp_t gfp, unsigned int order,
-		int preferred_nid, nodemask_t *nodemask)
+		int preferred_nid, nodemask_t *nodemask,
+		unsigned long user_addr)
 {
 	struct page *page;
 	unsigned int alloc_flags = ALLOC_WMARK_LOW;
 	gfp_t alloc_gfp; /* The gfp_t that was actually used for allocation */
-	struct alloc_context ac = { };
+	struct alloc_context ac = { .user_addr = user_addr };
 
 	/*
 	 * There are several places where we assume that the order value is sane
@@ -5254,10 +5258,12 @@ EXPORT_SYMBOL(__alloc_frozen_pages_noprof);
 
 struct page *__alloc_pages_noprof(gfp_t gfp, unsigned int order,
 		int preferred_nid, nodemask_t *nodemask)
+
 {
 	struct page *page;
 
-	page = __alloc_frozen_pages_noprof(gfp, order, preferred_nid, nodemask);
+	page = __alloc_frozen_pages_noprof(gfp, order, preferred_nid,
+					   nodemask, USER_ADDR_NONE);
 	if (page)
 		set_page_refcounted(page);
 	return page;
@@ -5300,7 +5306,8 @@ struct folio *vma_alloc_folio_noprof(gfp_t gfp, int order,
 		gfp |= __GFP_NOWARN;
 
 	pol = get_vma_policy(vma, addr, order, &ilx);
-	folio = folio_alloc_mpol_noprof(gfp, order, pol, ilx, numa_node_id());
+	folio = folio_alloc_mpol_user_noprof(gfp, order, pol, ilx,
+					     numa_node_id(), addr);
 	mpol_cond_put(pol);
 	return folio;
 }
@@ -5308,10 +5315,17 @@ struct folio *vma_alloc_folio_noprof(gfp_t gfp, int order,
 struct folio *vma_alloc_folio_noprof(gfp_t gfp, int order,
 		struct vm_area_struct *vma, unsigned long addr)
 {
+	struct page *page;
+
 	if (vma->vm_flags & VM_DROPPABLE)
 		gfp |= __GFP_NOWARN;
 
-	return folio_alloc_noprof(gfp, order);
+	page = __alloc_frozen_pages_noprof(gfp | __GFP_COMP, order,
+					   numa_node_id(), NULL, addr);
+	if (!page)
+		return NULL;
+	set_page_refcounted(page);
+	return page_rmappable_folio(page);
 }
 #endif
 EXPORT_SYMBOL(vma_alloc_folio_noprof);
@@ -6892,7 +6906,7 @@ static void split_free_frozen_pages(struct list_head *list, gfp_t gfp_mask)
 		list_for_each_entry_safe(page, next, &list[order], lru) {
 			int i;
 
-			post_alloc_hook(page, order, gfp_mask);
+			post_alloc_hook(page, order, gfp_mask, USER_ADDR_NONE);
 			if (!order)
 				continue;
 
@@ -7098,7 +7112,7 @@ int alloc_contig_frozen_range_noprof(unsigned long start, unsigned long end,
 		struct page *head = pfn_to_page(start);
 
 		check_new_pages(head, order);
-		prep_new_page(head, order, gfp_mask, 0);
+		prep_new_page(head, order, gfp_mask, 0, USER_ADDR_NONE);
 	} else {
 		ret = -EINVAL;
 		WARN(true, "PFN range: requested [%lu, %lu), allocated [%lu, %lu)\n",
@@ -7763,7 +7777,7 @@ struct page *alloc_frozen_pages_nolock_noprof(gfp_t gfp_flags, int nid, unsigned
 	gfp_t alloc_gfp = __GFP_NOWARN | __GFP_ZERO | __GFP_NOMEMALLOC | __GFP_COMP
 			| gfp_flags;
 	unsigned int alloc_flags = ALLOC_TRYLOCK;
-	struct alloc_context ac = { };
+	struct alloc_context ac = { .user_addr = USER_ADDR_NONE };
 	struct page *page;
 
 	VM_WARN_ON_ONCE(gfp_flags & ~__GFP_ACCOUNT);
diff --git a/mm/slub.c b/mm/slub.c
index 0baa906f39ab..74dd2d96941b 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -3275,7 +3275,7 @@ static inline struct slab *alloc_slab_page(gfp_t flags, int node,
 	else if (node == NUMA_NO_NODE)
 		page = alloc_frozen_pages(flags, order);
 	else
-		page = __alloc_frozen_pages(flags, order, node, NULL);
+		page = __alloc_frozen_pages(flags, order, node, NULL, USER_ADDR_NONE);
 
 	if (!page)
 		return NULL;
@@ -5235,7 +5235,7 @@ static void *___kmalloc_large_node(size_t size, gfp_t flags, int node)
 	if (node == NUMA_NO_NODE)
 		page = alloc_frozen_pages_noprof(flags, order);
 	else
-		page = __alloc_frozen_pages_noprof(flags, order, node, NULL);
+		page = __alloc_frozen_pages_noprof(flags, order, node, NULL, USER_ADDR_NONE);
 
 	if (page) {
 		ptr = page_address(page);
-- 
MST

[PATCH resend v6 04/30] mm: add folio_zero_user stub for configs without THP/HUGETLBFS

[Michael S. Tsirkin]

folio_zero_user() is defined in mm/memory.c under
CONFIG_TRANSPARENT_HUGEPAGE || CONFIG_HUGETLBFS.  A subsequent patch
will call it from post_alloc_hook() for all user page zeroing, so
configs without THP or HUGETLBFS will need a stub.

Add a macro in the #else branch that falls back to
clear_user_highpages(), which handles cache aliasing correctly on
VIPT architectures and is always available via highmem.h.

Without THP/HUGETLBFS, only order-0 user pages are allocated, so
the locality optimization in the real folio_zero_user() (zero near
the faulting address last) is not needed.
This also matches what vma_alloc_zeroed_movable_folio currently does.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Assisted-by: Claude:claude-opus-4-6
Assisted-by: cursor-agent:GPT-5.4-xhigh
---
 include/linux/mm.h | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index af23453e9dbd..3b1ca90fd435 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -5070,6 +5070,9 @@ long copy_folio_from_user(struct folio *dst_folio,
 			   const void __user *usr_src,
 			   bool allow_pagefault);
 
+#else /* !CONFIG_TRANSPARENT_HUGEPAGE && !CONFIG_HUGETLBFS */
+#define folio_zero_user(folio, addr_hint) \
+	clear_user_highpages(&(folio)->page, (addr_hint), folio_nr_pages(folio))
 #endif /* CONFIG_TRANSPARENT_HUGEPAGE || CONFIG_HUGETLBFS */
 
 #if MAX_NUMNODES > 1
-- 
MST

[PATCH resend v6 05/30] mm: page_alloc: move prep_compound_page before post_alloc_hook

[Michael S. Tsirkin]

Move prep_compound_page() before post_alloc_hook() in prep_new_page().

The next patch adds a folio_zero_user() call to post_alloc_hook(),
which uses folio_nr_pages() to determine how many pages to zero.
Without compound metadata set up first, folio_nr_pages() returns 1
for higher-order allocations, so only the first page would be zeroed.

All other operations in post_alloc_hook() (arch_alloc_page, KASAN,
debug, page owner, etc.) use raw page pointers with explicit order
counts and are unaffected by this reordering.

Note: compaction_alloc_noprof() has the opposite ordering
(post_alloc_hook before prep_compound_page).  This is fine because
compaction always passes USER_ADDR_NONE, so folio_zero_user() is
never called there and folio_nr_pages() is never reached inside
post_alloc_hook().

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Assisted-by: Claude:claude-opus-4-6
Assisted-by: cursor-agent:GPT-5.4-xhigh
---
 mm/page_alloc.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index c3c0f4e2baa7..f76d5271b5c6 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1864,11 +1864,11 @@ static void prep_new_page(struct page *page, unsigned int order, gfp_t gfp_flags
 							unsigned int alloc_flags,
 							unsigned long user_addr)
 {
-	post_alloc_hook(page, order, gfp_flags, user_addr);
-
 	if (order && (gfp_flags & __GFP_COMP))
 		prep_compound_page(page, order);
 
+	post_alloc_hook(page, order, gfp_flags, user_addr);
+
 	/*
 	 * page is set pfmemalloc when ALLOC_NO_WATERMARKS was necessary to
 	 * allocate the page. The expectation is that the caller is taking
-- 
MST

[PATCH resend v6 06/30] mm: use folio_zero_user for user pages in post_alloc_hook

[Michael S. Tsirkin]

When post_alloc_hook() needs to zero a page for an explicit
__GFP_ZERO allocation for a user page (user_addr is set), use folio_zero_user()
instead of kernel_init_pages().  This zeros near the faulting
address last, keeping those cachelines hot for the impending
user access.

folio_zero_user() is only used for explicit __GFP_ZERO, not for
init_on_alloc.  On architectures with virtually-indexed caches
(e.g., ARM), clear_user_highpage() performs per-line cache
operations; using it for init_on_alloc would add overhead that
kernel_init_pages() avoids (the page fault path flushes the
cache at PTE installation time regardless).

No functional change yet: current callers do not pass __GFP_ZERO
for user pages (they zero at the callsite instead).  Subsequent
patches will convert them.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Assisted-by: Claude:claude-opus-4-6
---
 mm/page_alloc.c | 17 ++++++++++++++---
 1 file changed, 14 insertions(+), 3 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index f76d5271b5c6..842f5080d728 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1851,9 +1851,20 @@ inline void post_alloc_hook(struct page *page, unsigned int order,
 		for (i = 0; i != 1 << order; ++i)
 			page_kasan_tag_reset(page + i);
 	}
-	/* If memory is still not initialized, initialize it now. */
-	if (init)
-		kernel_init_pages(page, 1 << order);
+	/*
+	 * If memory is still not initialized, initialize it now.
+	 * When __GFP_ZERO was explicitly requested and user_addr is set,
+	 * use folio_zero_user() which zeros near the faulting address
+	 * last, keeping those cachelines hot.  For init_on_alloc, use
+	 * kernel_init_pages() to avoid unnecessary cache flush overhead
+	 * on architectures with virtually-indexed caches.
+	 */
+	if (init) {
+		if ((gfp_flags & __GFP_ZERO) && user_addr != USER_ADDR_NONE)
+			folio_zero_user(page_folio(page), user_addr);
+		else
+			kernel_init_pages(page, 1 << order);
+	}
 
 	set_page_owner(page, order, gfp_flags);
 	page_table_check_alloc(page, order);
-- 
MST

[PATCH resend v6 07/30] mm: use __GFP_ZERO in vma_alloc_zeroed_movable_folio

[Michael S. Tsirkin]

Now that post_alloc_hook() handles cache-friendly user page
zeroing via folio_zero_user(), convert vma_alloc_zeroed_movable_folio()
to pass __GFP_ZERO instead of zeroing at the callsite.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Assisted-by: Claude:claude-opus-4-6
---
 include/linux/highmem.h | 9 ++-------
 1 file changed, 2 insertions(+), 7 deletions(-)

diff --git a/include/linux/highmem.h b/include/linux/highmem.h
index af03db851a1d..ffa683f64f1d 100644
--- a/include/linux/highmem.h
+++ b/include/linux/highmem.h
@@ -320,13 +320,8 @@ static inline
 struct folio *vma_alloc_zeroed_movable_folio(struct vm_area_struct *vma,
 				   unsigned long vaddr)
 {
-	struct folio *folio;
-
-	folio = vma_alloc_folio(GFP_HIGHUSER_MOVABLE, 0, vma, vaddr);
-	if (folio && user_alloc_needs_zeroing())
-		clear_user_highpage(&folio->page, vaddr);
-
-	return folio;
+	return vma_alloc_folio(GFP_HIGHUSER_MOVABLE | __GFP_ZERO,
+			      0, vma, vaddr);
 }
 #endif
 
-- 
MST

[PATCH resend v6 08/30] mm: remove arch vma_alloc_zeroed_movable_folio overrides

[Michael S. Tsirkin]

Now that the generic vma_alloc_zeroed_movable_folio() uses
__GFP_ZERO, the arch-specific macros on alpha, m68k, s390, and
x86 that did the same thing are redundant.  Remove them.

arm64 is not affected: it has a real function override that
handles MTE tag zeroing, not just __GFP_ZERO.

Suggested-by: David Hildenbrand <david@kernel.org>
Acked-by: Magnus Lindholm <linmag7@gmail.com>
Acked-by: Greg Ungerer <gerg@linux-m68k.org>
Acked-by: Geert Uytterhoeven <geert@linux-m68k.org> # m68k
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---
 arch/alpha/include/asm/page.h   | 3 ---
 arch/m68k/include/asm/page_no.h | 3 ---
 arch/s390/include/asm/page.h    | 3 ---
 arch/x86/include/asm/page.h     | 3 ---
 4 files changed, 12 deletions(-)

diff --git a/arch/alpha/include/asm/page.h b/arch/alpha/include/asm/page.h
index 59d01f9b77f6..4327029cd660 100644
--- a/arch/alpha/include/asm/page.h
+++ b/arch/alpha/include/asm/page.h
@@ -12,9 +12,6 @@
 
 extern void clear_page(void *page);
 
-#define vma_alloc_zeroed_movable_folio(vma, vaddr) \
-	vma_alloc_folio(GFP_HIGHUSER_MOVABLE | __GFP_ZERO, 0, vma, vaddr)
-
 extern void copy_page(void * _to, void * _from);
 #define copy_user_page(to, from, vaddr, pg)	copy_page(to, from)
 
diff --git a/arch/m68k/include/asm/page_no.h b/arch/m68k/include/asm/page_no.h
index d2532bc407ef..f511b763a235 100644
--- a/arch/m68k/include/asm/page_no.h
+++ b/arch/m68k/include/asm/page_no.h
@@ -12,9 +12,6 @@ extern unsigned long memory_end;
 
 #define copy_user_page(to, from, vaddr, pg)	copy_page(to, from)
 
-#define vma_alloc_zeroed_movable_folio(vma, vaddr) \
-	vma_alloc_folio(GFP_HIGHUSER_MOVABLE | __GFP_ZERO, 0, vma, vaddr)
-
 #define __pa(vaddr)		((unsigned long)(vaddr))
 #define __va(paddr)		((void *)((unsigned long)(paddr)))
 
diff --git a/arch/s390/include/asm/page.h b/arch/s390/include/asm/page.h
index 56da819a79e6..e995d2a413f9 100644
--- a/arch/s390/include/asm/page.h
+++ b/arch/s390/include/asm/page.h
@@ -67,9 +67,6 @@ static inline void copy_page(void *to, void *from)
 
 #define copy_user_page(to, from, vaddr, pg)	copy_page(to, from)
 
-#define vma_alloc_zeroed_movable_folio(vma, vaddr) \
-	vma_alloc_folio(GFP_HIGHUSER_MOVABLE | __GFP_ZERO, 0, vma, vaddr)
-
 #ifdef CONFIG_STRICT_MM_TYPECHECKS
 #define STRICT_MM_TYPECHECKS
 #endif
diff --git a/arch/x86/include/asm/page.h b/arch/x86/include/asm/page.h
index 416dc88e35c1..92fa975b46f3 100644
--- a/arch/x86/include/asm/page.h
+++ b/arch/x86/include/asm/page.h
@@ -28,9 +28,6 @@ static inline void copy_user_page(void *to, void *from, unsigned long vaddr,
 	copy_page(to, from);
 }
 
-#define vma_alloc_zeroed_movable_folio(vma, vaddr) \
-	vma_alloc_folio(GFP_HIGHUSER_MOVABLE | __GFP_ZERO, 0, vma, vaddr)
-
 #ifndef __pa
 #define __pa(x)		__phys_addr((unsigned long)(x))
 #endif
-- 
MST

[PATCH resend v6 09/30] mm: alloc_anon_folio: pass raw fault address to vma_alloc_folio

[Michael S. Tsirkin]

Pass vmf->address directly instead of ALIGN_DOWN(vmf->address, ...).
vma_alloc_folio_noprof now aligns internally for NUMA interleave,
and post_alloc_hook will use the raw address for cache-friendly
zeroing via folio_zero_user().

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Assisted-by: Claude:claude-opus-4-6
Assisted-by: cursor-agent:GPT-5.4-xhigh
---
 mm/memory.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/mm/memory.c b/mm/memory.c
index ea6568571131..0824441a6ba1 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -5252,8 +5252,7 @@ static struct folio *alloc_anon_folio(struct vm_fault *vmf)
 	/* Try allocating the highest of the remaining orders. */
 	gfp = vma_thp_gfp_mask(vma);
 	while (orders) {
-		addr = ALIGN_DOWN(vmf->address, PAGE_SIZE << order);
-		folio = vma_alloc_folio(gfp, order, vma, addr);
+		folio = vma_alloc_folio(gfp, order, vma, vmf->address);
 		if (folio) {
 			if (mem_cgroup_charge(folio, vma->vm_mm, gfp)) {
 				count_mthp_stat(order, MTHP_STAT_ANON_FAULT_FALLBACK_CHARGE);
-- 
MST

[PATCH resend v6 10/30] mm: alloc_swap_folio: pass raw fault address to vma_alloc_folio

[Michael S. Tsirkin]

Same change as the previous patch but for alloc_swap_folio:
pass vmf->address directly instead of ALIGN_DOWN(vmf->address, ...).

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Assisted-by: Claude:claude-opus-4-6
Assisted-by: cursor-agent:GPT-5.4-xhigh
---
 mm/memory.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/mm/memory.c b/mm/memory.c
index 0824441a6ba1..74523bc00d8a 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -4734,8 +4734,7 @@ static struct folio *alloc_swap_folio(struct vm_fault *vmf)
 	/* Try allocating the highest of the remaining orders. */
 	gfp = vma_thp_gfp_mask(vma);
 	while (orders) {
-		addr = ALIGN_DOWN(vmf->address, PAGE_SIZE << order);
-		folio = vma_alloc_folio(gfp, order, vma, addr);
+		folio = vma_alloc_folio(gfp, order, vma, vmf->address);
 		if (folio) {
 			if (!mem_cgroup_swapin_charge_folio(folio, vma->vm_mm,
 							    gfp, entry))
-- 
MST

[PATCH resend v6 11/30] mm: use __GFP_ZERO in alloc_anon_folio

[Michael S. Tsirkin]

Convert alloc_anon_folio() to pass __GFP_ZERO instead of zeroing
at the callsite. post_alloc_hook uses the fault address passed
through vma_alloc_folio for cache-friendly zeroing.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Assisted-by: Claude:claude-opus-4-6
---
 mm/memory.c | 11 +----------
 1 file changed, 1 insertion(+), 10 deletions(-)

diff --git a/mm/memory.c b/mm/memory.c
index 74523bc00d8a..f3f1bc66366d 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -5249,7 +5249,7 @@ static struct folio *alloc_anon_folio(struct vm_fault *vmf)
 		goto fallback;
 
 	/* Try allocating the highest of the remaining orders. */
-	gfp = vma_thp_gfp_mask(vma);
+	gfp = vma_thp_gfp_mask(vma) | __GFP_ZERO;
 	while (orders) {
 		folio = vma_alloc_folio(gfp, order, vma, vmf->address);
 		if (folio) {
@@ -5259,15 +5259,6 @@ static struct folio *alloc_anon_folio(struct vm_fault *vmf)
 				goto next;
 			}
 			folio_throttle_swaprate(folio, gfp);
-			/*
-			 * When a folio is not zeroed during allocation
-			 * (__GFP_ZERO not used) or user folios require special
-			 * handling, folio_zero_user() is used to make sure
-			 * that the page corresponding to the faulting address
-			 * will be hot in the cache after zeroing.
-			 */
-			if (user_alloc_needs_zeroing())
-				folio_zero_user(folio, vmf->address);
 			return folio;
 		}
 next:
-- 
MST

[PATCH resend v6 12/30] mm: vma_alloc_anon_folio_pmd: pass raw fault address to vma_alloc_folio

[Michael S. Tsirkin]

Now that vma_alloc_folio aligns the address internally, drop the
redundant HPAGE_PMD_MASK alignment at the callsite.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---
 mm/huge_memory.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 970e077019b7..d689e6491ddb 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1337,7 +1337,7 @@ static struct folio *vma_alloc_anon_folio_pmd(struct vm_area_struct *vma,
 	const int order = HPAGE_PMD_ORDER;
 	struct folio *folio;
 
-	folio = vma_alloc_folio(gfp, order, vma, addr & HPAGE_PMD_MASK);
+	folio = vma_alloc_folio(gfp, order, vma, addr);
 
 	if (unlikely(!folio)) {
 		count_vm_event(THP_FAULT_FALLBACK);
-- 
MST

[PATCH resend v6 13/30] mm: use __GFP_ZERO in vma_alloc_anon_folio_pmd

[Michael S. Tsirkin]

Convert vma_alloc_anon_folio_pmd() to pass __GFP_ZERO instead of
zeroing at the callsite. post_alloc_hook uses the fault address
passed through vma_alloc_folio for cache-friendly zeroing.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Assisted-by: Claude:claude-opus-4-6
---
 mm/huge_memory.c | 10 +---------
 1 file changed, 1 insertion(+), 9 deletions(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index d689e6491ddb..9845c920c29c 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1333,7 +1333,7 @@ EXPORT_SYMBOL_GPL(thp_get_unmapped_area);
 static struct folio *vma_alloc_anon_folio_pmd(struct vm_area_struct *vma,
 		unsigned long addr)
 {
-	gfp_t gfp = vma_thp_gfp_mask(vma);
+	gfp_t gfp = vma_thp_gfp_mask(vma) | __GFP_ZERO;
 	const int order = HPAGE_PMD_ORDER;
 	struct folio *folio;
 
@@ -1356,14 +1356,6 @@ static struct folio *vma_alloc_anon_folio_pmd(struct vm_area_struct *vma,
 	}
 	folio_throttle_swaprate(folio, gfp);
 
-       /*
-	* When a folio is not zeroed during allocation (__GFP_ZERO not used)
-	* or user folios require special handling, folio_zero_user() is used to
-	* make sure that the page corresponding to the faulting address will be
-	* hot in the cache after zeroing.
-	*/
-	if (user_alloc_needs_zeroing())
-		folio_zero_user(folio, addr);
 	/*
 	 * The memory barrier inside __folio_mark_uptodate makes sure that
 	 * folio_zero_user writes become visible before the set_pmd_at()
-- 
MST

[PATCH resend v6 14/30] mm: hugetlb: use __GFP_ZERO and skip zeroing for zeroed pages

[Michael S. Tsirkin]

Convert the hugetlb fault and fallocate paths to use __GFP_ZERO.
For pages allocated from the buddy allocator, post_alloc_hook()
handles zeroing.

Hugetlb surplus pages need special handling because they can be
pre-allocated into the pool during mmap (by hugetlb_acct_memory)
before any page fault.  Pool pages are kept around and may need
zeroing long after buddy allocation, so a buddy-level zeroed
hint (consumed at allocation time) cannot track their state.

Add a bool *zeroed output parameter to alloc_hugetlb_folio()
so callers know whether the page needs zeroing.  Buddy-allocated
pages are always zeroed (zeroed by post_alloc_hook).  Pool
pages use a new HPG_zeroed flag to track whether the page is
known-zero (freshly buddy-allocated, never mapped to userspace).
The flag is set in alloc_surplus_hugetlb_folio() after buddy
allocation and cleared in free_huge_folio() when a user-mapped
page returns to the pool.

Callers that do not need zeroing (CoW, migration) pass NULL for
zeroed and 0 for gfp.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Assisted-by: Claude:claude-opus-4-6
Assisted-by: cursor-agent:GPT-5.4-xhigh
---
 fs/hugetlbfs/inode.c    | 10 ++++++--
 include/linux/hugetlb.h |  8 +++++--
 mm/hugetlb.c            | 52 ++++++++++++++++++++++++++++++-----------
 3 files changed, 53 insertions(+), 17 deletions(-)

diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
index 8b05bec08e04..24e42cb10ade 100644
--- a/fs/hugetlbfs/inode.c
+++ b/fs/hugetlbfs/inode.c
@@ -810,14 +810,20 @@ static long hugetlbfs_fallocate(struct file *file, int mode, loff_t offset,
 		 * folios in these areas, we need to consume the reserves
 		 * to keep reservation accounting consistent.
 		 */
-		folio = alloc_hugetlb_folio(&pseudo_vma, addr, false);
+		{
+		bool zeroed;
+
+		folio = alloc_hugetlb_folio(&pseudo_vma, addr, false,
+					   __GFP_ZERO, &zeroed);
 		if (IS_ERR(folio)) {
 			mutex_unlock(&hugetlb_fault_mutex_table[hash]);
 			error = PTR_ERR(folio);
 			goto out;
 		}
-		folio_zero_user(folio, addr);
+		if (!zeroed)
+			folio_zero_user(folio, addr);
 		__folio_mark_uptodate(folio);
+		}
 		error = hugetlb_add_to_page_cache(folio, mapping, index);
 		if (unlikely(error)) {
 			restore_reserve_on_error(h, &pseudo_vma, addr, folio);
diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
index 93418625d3c5..950e1702fbd8 100644
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -599,6 +599,7 @@ enum hugetlb_page_flags {
 	HPG_vmemmap_optimized,
 	HPG_raw_hwp_unreliable,
 	HPG_cma,
+	HPG_zeroed,
 	__NR_HPAGEFLAGS,
 };
 
@@ -659,6 +660,7 @@ HPAGEFLAG(Freed, freed)
 HPAGEFLAG(VmemmapOptimized, vmemmap_optimized)
 HPAGEFLAG(RawHwpUnreliable, raw_hwp_unreliable)
 HPAGEFLAG(Cma, cma)
+HPAGEFLAG(Zeroed, zeroed)
 
 #ifdef CONFIG_HUGETLB_PAGE
 
@@ -706,7 +708,8 @@ int isolate_or_dissolve_huge_folio(struct folio *folio, struct list_head *list);
 int replace_free_hugepage_folios(unsigned long start_pfn, unsigned long end_pfn);
 void wait_for_freed_hugetlb_folios(void);
 struct folio *alloc_hugetlb_folio(struct vm_area_struct *vma,
-				unsigned long addr, bool cow_from_owner);
+				unsigned long addr, bool cow_from_owner,
+				gfp_t gfp, bool *zeroed);
 struct folio *alloc_hugetlb_folio_nodemask(struct hstate *h, int preferred_nid,
 				nodemask_t *nmask, gfp_t gfp_mask,
 				bool allow_alloc_fallback);
@@ -1131,7 +1134,8 @@ static inline void wait_for_freed_hugetlb_folios(void)
 
 static inline struct folio *alloc_hugetlb_folio(struct vm_area_struct *vma,
 					   unsigned long addr,
-					   bool cow_from_owner)
+					   bool cow_from_owner,
+					   gfp_t gfp, bool *zeroed)
 {
 	return NULL;
 }
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index a999f3ead852..8710366d14b7 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -1708,6 +1708,9 @@ void free_huge_folio(struct folio *folio)
 	int nid = folio_nid(folio);
 	struct hugepage_subpool *spool = hugetlb_folio_subpool(folio);
 	bool restore_reserve;
+
+	/* Page was mapped to userspace; no longer known-zero */
+	folio_clear_hugetlb_zeroed(folio);
 	unsigned long flags;
 
 	VM_BUG_ON_FOLIO(folio_ref_count(folio), folio);
@@ -2110,6 +2113,10 @@ static struct folio *alloc_surplus_hugetlb_folio(struct hstate *h,
 	if (!folio)
 		return NULL;
 
+	/* Mark as known-zero only if __GFP_ZERO was requested */
+	if (gfp_mask & __GFP_ZERO)
+		folio_set_hugetlb_zeroed(folio);
+
 	spin_lock_irq(&hugetlb_lock);
 	/*
 	 * nr_huge_pages needs to be adjusted within the same lock cycle
@@ -2173,11 +2180,11 @@ static struct folio *alloc_migrate_hugetlb_folio(struct hstate *h, gfp_t gfp_mas
  */
 static
 struct folio *alloc_buddy_hugetlb_folio_with_mpol(struct hstate *h,
-		struct vm_area_struct *vma, unsigned long addr)
+		struct vm_area_struct *vma, unsigned long addr, gfp_t gfp)
 {
 	struct folio *folio = NULL;
 	struct mempolicy *mpol;
-	gfp_t gfp_mask = htlb_alloc_mask(h);
+	gfp_t gfp_mask = htlb_alloc_mask(h) | gfp;
 	int nid;
 	nodemask_t *nodemask;
 
@@ -2874,7 +2881,8 @@ typedef enum {
  * When it's set, the allocation will bypass all vma level reservations.
  */
 struct folio *alloc_hugetlb_folio(struct vm_area_struct *vma,
-				    unsigned long addr, bool cow_from_owner)
+				    unsigned long addr, bool cow_from_owner,
+				    gfp_t gfp, bool *zeroed)
 {
 	struct hugepage_subpool *spool = subpool_vma(vma);
 	struct hstate *h = hstate_vma(vma);
@@ -2883,7 +2891,9 @@ struct folio *alloc_hugetlb_folio(struct vm_area_struct *vma,
 	map_chg_state map_chg;
 	int ret, idx;
 	struct hugetlb_cgroup *h_cg = NULL;
-	gfp_t gfp = htlb_alloc_mask(h) | __GFP_RETRY_MAYFAIL;
+	bool from_pool;
+
+	gfp |= htlb_alloc_mask(h) | __GFP_RETRY_MAYFAIL;
 
 	idx = hstate_index(h);
 
@@ -2951,13 +2961,15 @@ struct folio *alloc_hugetlb_folio(struct vm_area_struct *vma,
 	folio = dequeue_hugetlb_folio_vma(h, vma, addr, gbl_chg);
 	if (!folio) {
 		spin_unlock_irq(&hugetlb_lock);
-		folio = alloc_buddy_hugetlb_folio_with_mpol(h, vma, addr);
+		folio = alloc_buddy_hugetlb_folio_with_mpol(h, vma, addr, gfp);
 		if (!folio)
 			goto out_uncharge_cgroup;
 		spin_lock_irq(&hugetlb_lock);
 		list_add(&folio->lru, &h->hugepage_activelist);
 		folio_ref_unfreeze(folio, 1);
-		/* Fall through */
+		from_pool = false;
+	} else {
+		from_pool = true;
 	}
 
 	/*
@@ -2980,6 +2992,14 @@ struct folio *alloc_hugetlb_folio(struct vm_area_struct *vma,
 
 	spin_unlock_irq(&hugetlb_lock);
 
+	if (zeroed) {
+		if (from_pool)
+			*zeroed = folio_test_hugetlb_zeroed(folio);
+		else
+			*zeroed = true; /* buddy-allocated, zeroed by post_alloc_hook */
+		folio_clear_hugetlb_zeroed(folio);
+	}
+
 	hugetlb_set_folio_subpool(folio, spool);
 
 	if (map_chg != MAP_CHG_ENFORCED) {
@@ -4988,7 +5008,7 @@ int copy_hugetlb_page_range(struct mm_struct *dst, struct mm_struct *src,
 				spin_unlock(src_ptl);
 				spin_unlock(dst_ptl);
 				/* Do not use reserve as it's private owned */
-				new_folio = alloc_hugetlb_folio(dst_vma, addr, false);
+				new_folio = alloc_hugetlb_folio(dst_vma, addr, false, 0, NULL);
 				if (IS_ERR(new_folio)) {
 					folio_put(pte_folio);
 					ret = PTR_ERR(new_folio);
@@ -5517,7 +5537,7 @@ static vm_fault_t hugetlb_wp(struct vm_fault *vmf)
 	 * be acquired again before returning to the caller, as expected.
 	 */
 	spin_unlock(vmf->ptl);
-	new_folio = alloc_hugetlb_folio(vma, vmf->address, cow_from_owner);
+	new_folio = alloc_hugetlb_folio(vma, vmf->address, cow_from_owner, 0, NULL);
 
 	if (IS_ERR(new_folio)) {
 		/*
@@ -5711,7 +5731,7 @@ static vm_fault_t hugetlb_no_page(struct address_space *mapping,
 			struct vm_fault *vmf)
 {
 	u32 hash = hugetlb_fault_mutex_hash(mapping, vmf->pgoff);
-	bool new_folio, new_anon_folio = false;
+	bool new_folio, new_anon_folio = false, zeroed;
 	struct vm_area_struct *vma = vmf->vma;
 	struct mm_struct *mm = vma->vm_mm;
 	struct hstate *h = hstate_vma(vma);
@@ -5777,7 +5797,8 @@ static vm_fault_t hugetlb_no_page(struct address_space *mapping,
 				goto out;
 		}
 
-		folio = alloc_hugetlb_folio(vma, vmf->address, false);
+		folio = alloc_hugetlb_folio(vma, vmf->address, false,
+					   __GFP_ZERO, &zeroed);
 		if (IS_ERR(folio)) {
 			/*
 			 * Returning error will result in faulting task being
@@ -5797,7 +5818,12 @@ static vm_fault_t hugetlb_no_page(struct address_space *mapping,
 				ret = 0;
 			goto out;
 		}
-		folio_zero_user(folio, vmf->real_address);
+		/*
+		 * Buddy-allocated pages are zeroed in post_alloc_hook().
+		 * Pool pages bypass the allocator, zero them here.
+		 */
+		if (!zeroed)
+			folio_zero_user(folio, vmf->real_address);
 		__folio_mark_uptodate(folio);
 		new_folio = true;
 
@@ -6236,7 +6262,7 @@ int hugetlb_mfill_atomic_pte(pte_t *dst_pte,
 			goto out;
 		}
 
-		folio = alloc_hugetlb_folio(dst_vma, dst_addr, false);
+		folio = alloc_hugetlb_folio(dst_vma, dst_addr, false, 0, NULL);
 		if (IS_ERR(folio)) {
 			pte_t *actual_pte = hugetlb_walk(dst_vma, dst_addr, PMD_SIZE);
 			if (actual_pte) {
@@ -6283,7 +6309,7 @@ int hugetlb_mfill_atomic_pte(pte_t *dst_pte,
 			goto out;
 		}
 
-		folio = alloc_hugetlb_folio(dst_vma, dst_addr, false);
+		folio = alloc_hugetlb_folio(dst_vma, dst_addr, false, 0, NULL);
 		if (IS_ERR(folio)) {
 			folio_put(*foliop);
 			ret = -ENOMEM;
-- 
MST

[PATCH resend v6 15/30] mm: memfd: skip zeroing for zeroed hugetlb pool pages

[Michael S. Tsirkin]

gather_surplus_pages() pre-allocates hugetlb pages into the pool
during mmap.  Pass __GFP_ZERO so these pages are zeroed by the
buddy allocator, and HPG_zeroed is set by alloc_surplus_hugetlb_folio.

Add bool *zeroed output to alloc_hugetlb_folio_reserve() so
callers can check whether the pool page is known-zero.  memfd's
memfd_alloc_folio() uses this to skip the explicit folio_zero_user()
when the page is already zero.

This avoids redundant zeroing for memfd hugetlb pages that were
pre-allocated into the pool and never mapped to userspace.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Assisted-by: Claude:claude-opus-4-6
---
 include/linux/hugetlb.h |  6 ++++--
 mm/hugetlb.c            | 11 +++++++++--
 mm/memfd.c              | 14 ++++++++------
 3 files changed, 21 insertions(+), 10 deletions(-)

diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
index 950e1702fbd8..c4e66a371fce 100644
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -714,7 +714,8 @@ struct folio *alloc_hugetlb_folio_nodemask(struct hstate *h, int preferred_nid,
 				nodemask_t *nmask, gfp_t gfp_mask,
 				bool allow_alloc_fallback);
 struct folio *alloc_hugetlb_folio_reserve(struct hstate *h, int preferred_nid,
-					  nodemask_t *nmask, gfp_t gfp_mask);
+					  nodemask_t *nmask, gfp_t gfp_mask,
+					  bool *zeroed);
 
 int hugetlb_add_to_page_cache(struct folio *folio, struct address_space *mapping,
 			pgoff_t idx);
@@ -1142,7 +1143,8 @@ static inline struct folio *alloc_hugetlb_folio(struct vm_area_struct *vma,
 
 static inline struct folio *
 alloc_hugetlb_folio_reserve(struct hstate *h, int preferred_nid,
-			    nodemask_t *nmask, gfp_t gfp_mask)
+			    nodemask_t *nmask, gfp_t gfp_mask,
+			    bool *zeroed)
 {
 	return NULL;
 }
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 8710366d14b7..03ad5c1e0655 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -2205,7 +2205,7 @@ struct folio *alloc_buddy_hugetlb_folio_with_mpol(struct hstate *h,
 }
 
 struct folio *alloc_hugetlb_folio_reserve(struct hstate *h, int preferred_nid,
-		nodemask_t *nmask, gfp_t gfp_mask)
+		nodemask_t *nmask, gfp_t gfp_mask, bool *zeroed)
 {
 	struct folio *folio;
 
@@ -2221,6 +2221,12 @@ struct folio *alloc_hugetlb_folio_reserve(struct hstate *h, int preferred_nid,
 		h->resv_huge_pages--;
 
 	spin_unlock_irq(&hugetlb_lock);
+
+	if (zeroed && folio) {
+		*zeroed = folio_test_hugetlb_zeroed(folio);
+		folio_clear_hugetlb_zeroed(folio);
+	}
+
 	return folio;
 }
 
@@ -2305,7 +2311,8 @@ static int gather_surplus_pages(struct hstate *h, long delta)
 		 * It is okay to use NUMA_NO_NODE because we use numa_mem_id()
 		 * down the road to pick the current node if that is the case.
 		 */
-		folio = alloc_surplus_hugetlb_folio(h, htlb_alloc_mask(h),
+		folio = alloc_surplus_hugetlb_folio(h,
+						    htlb_alloc_mask(h) | __GFP_ZERO,
 						    NUMA_NO_NODE, &alloc_nodemask,
 						    USER_ADDR_NONE);
 		if (!folio) {
diff --git a/mm/memfd.c b/mm/memfd.c
index fb425f4e315f..5518f7d2d91f 100644
--- a/mm/memfd.c
+++ b/mm/memfd.c
@@ -69,6 +69,7 @@ struct folio *memfd_alloc_folio(struct file *memfd, pgoff_t idx)
 #ifdef CONFIG_HUGETLB_PAGE
 	struct folio *folio;
 	gfp_t gfp_mask;
+	bool zeroed;
 
 	if (is_file_hugepages(memfd)) {
 		/*
@@ -93,17 +94,18 @@ struct folio *memfd_alloc_folio(struct file *memfd, pgoff_t idx)
 		folio = alloc_hugetlb_folio_reserve(h,
 						    numa_node_id(),
 						    NULL,
-						    gfp_mask);
+						    gfp_mask,
+						    &zeroed);
 		if (folio) {
 			u32 hash;
 
 			/*
-			 * Zero the folio to prevent information leaks to userspace.
-			 * Use folio_zero_user() which is optimized for huge/gigantic
-			 * pages. Pass 0 as addr_hint since this is not a faulting path
-			 *  and we don't have a user virtual address yet.
+			 * Zero the folio to prevent information leaks to
+			 * userspace.  Skip if the pool page is known-zero
+			 * (HPG_zeroed set during pool pre-allocation).
 			 */
-			folio_zero_user(folio, 0);
+			if (!zeroed)
+				folio_zero_user(folio, 0);
 
 			/*
 			 * Mark the folio uptodate before adding to page cache,
-- 
MST

[PATCH resend v6 16/30] mm: page_reporting: allow driver to set batch capacity

[Michael S. Tsirkin]

Add a capacity field to page_reporting_dev_info so drivers can
control the maximum number of pages per report batch. This is
useful when the driver needs to reserve virtqueue descriptors for
metadata (e.g., a bitmap buffer) alongside the page buffers.

The value is capped at PAGE_REPORTING_CAPACITY and rounded down
to a power of 2. If unset (0), defaults to PAGE_REPORTING_CAPACITY.

The virtio_balloon driver sets capacity to the reporting virtqueue
size, letting page_reporting adapt to whatever the device provides.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Assisted-by: Claude:claude-opus-4-6
---
 drivers/virtio/virtio_balloon.c |  5 +----
 include/linux/page_reporting.h  |  3 +++
 mm/page_reporting.c             | 26 +++++++++++++++-----------
 3 files changed, 19 insertions(+), 15 deletions(-)

diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
index f6c2dff33f8a..6a1a610c2cb1 100644
--- a/drivers/virtio/virtio_balloon.c
+++ b/drivers/virtio/virtio_balloon.c
@@ -1017,10 +1017,6 @@ static int virtballoon_probe(struct virtio_device *vdev)
 		unsigned int capacity;
 
 		capacity = virtqueue_get_vring_size(vb->reporting_vq);
-		if (capacity < PAGE_REPORTING_CAPACITY) {
-			err = -ENOSPC;
-			goto out_unregister_oom;
-		}
 
 		vb->pr_dev_info.order = PAGE_REPORTING_ORDER_UNSPECIFIED;
 
@@ -1041,6 +1037,7 @@ static int virtballoon_probe(struct virtio_device *vdev)
 		vb->pr_dev_info.order = 5;
 #endif
 
+		vb->pr_dev_info.capacity = capacity;
 		err = page_reporting_register(&vb->pr_dev_info);
 		if (err)
 			goto out_unregister_oom;
diff --git a/include/linux/page_reporting.h b/include/linux/page_reporting.h
index 9d4ca5c218a0..5ab5be02fa15 100644
--- a/include/linux/page_reporting.h
+++ b/include/linux/page_reporting.h
@@ -22,6 +22,9 @@ struct page_reporting_dev_info {
 
 	/* Minimal order of page reporting */
 	unsigned int order;
+
+	/* Max pages per report batch (default PAGE_REPORTING_CAPACITY) */
+	unsigned int capacity;
 };
 
 /* Tear-down and bring-up for page reporting devices */
diff --git a/mm/page_reporting.c b/mm/page_reporting.c
index 7418f2e500bb..006f7cdddc18 100644
--- a/mm/page_reporting.c
+++ b/mm/page_reporting.c
@@ -174,10 +174,10 @@ page_reporting_cycle(struct page_reporting_dev_info *prdev, struct zone *zone,
 	 * list processed. This should result in us reporting all pages on
 	 * an idle system in about 30 seconds.
 	 *
-	 * The division here should be cheap since PAGE_REPORTING_CAPACITY
-	 * should always be a power of 2.
+	 * The division here should be cheap since capacity should
+	 * always be a power of 2.
 	 */
-	budget = DIV_ROUND_UP(area->nr_free, PAGE_REPORTING_CAPACITY * 16);
+	budget = DIV_ROUND_UP(area->nr_free, prdev->capacity * 16);
 
 	/* loop through free list adding unreported pages to sg list */
 	list_for_each_entry_safe(page, next, list, lru) {
@@ -222,10 +222,10 @@ page_reporting_cycle(struct page_reporting_dev_info *prdev, struct zone *zone,
 		spin_unlock_irq(&zone->lock);
 
 		/* begin processing pages in local list */
-		err = prdev->report(prdev, sgl, PAGE_REPORTING_CAPACITY);
+		err = prdev->report(prdev, sgl, prdev->capacity);
 
 		/* reset offset since the full list was reported */
-		*offset = PAGE_REPORTING_CAPACITY;
+		*offset = prdev->capacity;
 
 		/* update budget to reflect call to report function */
 		budget--;
@@ -234,7 +234,7 @@ page_reporting_cycle(struct page_reporting_dev_info *prdev, struct zone *zone,
 		spin_lock_irq(&zone->lock);
 
 		/* flush reported pages from the sg list */
-		page_reporting_drain(prdev, sgl, PAGE_REPORTING_CAPACITY, !err);
+		page_reporting_drain(prdev, sgl, prdev->capacity, !err);
 
 		/*
 		 * Reset next to first entry, the old next isn't valid
@@ -260,13 +260,13 @@ static int
 page_reporting_process_zone(struct page_reporting_dev_info *prdev,
 			    struct scatterlist *sgl, struct zone *zone)
 {
-	unsigned int order, mt, leftover, offset = PAGE_REPORTING_CAPACITY;
+	unsigned int order, mt, leftover, offset = prdev->capacity;
 	unsigned long watermark;
 	int err = 0;
 
 	/* Generate minimum watermark to be able to guarantee progress */
 	watermark = low_wmark_pages(zone) +
-		    (PAGE_REPORTING_CAPACITY << page_reporting_order);
+		    (prdev->capacity << page_reporting_order);
 
 	/*
 	 * Cancel request if insufficient free memory or if we failed
@@ -290,7 +290,7 @@ page_reporting_process_zone(struct page_reporting_dev_info *prdev,
 	}
 
 	/* report the leftover pages before going idle */
-	leftover = PAGE_REPORTING_CAPACITY - offset;
+	leftover = prdev->capacity - offset;
 	if (leftover) {
 		sgl = &sgl[offset];
 		err = prdev->report(prdev, sgl, leftover);
@@ -322,11 +322,11 @@ static void page_reporting_process(struct work_struct *work)
 	atomic_set(&prdev->state, state);
 
 	/* allocate scatterlist to store pages being reported on */
-	sgl = kmalloc_objs(*sgl, PAGE_REPORTING_CAPACITY);
+	sgl = kmalloc_objs(*sgl, prdev->capacity);
 	if (!sgl)
 		goto err_out;
 
-	sg_init_table(sgl, PAGE_REPORTING_CAPACITY);
+	sg_init_table(sgl, prdev->capacity);
 
 	for_each_zone(zone) {
 		err = page_reporting_process_zone(prdev, sgl, zone);
@@ -377,6 +377,10 @@ int page_reporting_register(struct page_reporting_dev_info *prdev)
 			page_reporting_order = pageblock_order;
 	}
 
+	if (!prdev->capacity || prdev->capacity > PAGE_REPORTING_CAPACITY)
+		prdev->capacity = PAGE_REPORTING_CAPACITY;
+	prdev->capacity = rounddown_pow_of_two(prdev->capacity);
+
 	/* initialize state and work structures */
 	atomic_set(&prdev->state, PAGE_REPORTING_IDLE);
 	INIT_DELAYED_WORK(&prdev->work, &page_reporting_process);
-- 
MST

[PATCH resend v6 17/30] mm: page_alloc: propagate PageReported flag across buddy splits

[Michael S. Tsirkin]

When a reported free page is split via expand() to satisfy a
smaller allocation, the sub-pages placed back on the free lists
lose the PageReported flag.  This means they will be unnecessarily
re-reported to the hypervisor in the next reporting cycle, wasting
work.

Propagate the PageReported flag to sub-pages during expand(),
both in page_del_and_expand() and try_to_claim_block(), so
that they are recognized as already-reported.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Assisted-by: Claude:claude-opus-4-6
---
 mm/page_alloc.c | 18 +++++++++++++++---
 1 file changed, 15 insertions(+), 3 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 842f5080d728..76f39dd026ff 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1699,7 +1699,7 @@ struct page *__pageblock_pfn_to_page(unsigned long start_pfn,
  * -- nyc
  */
 static inline unsigned int expand(struct zone *zone, struct page *page, int low,
-				  int high, int migratetype)
+				  int high, int migratetype, bool reported)
 {
 	unsigned int size = 1 << high;
 	unsigned int nr_added = 0;
@@ -1721,6 +1721,15 @@ static inline unsigned int expand(struct zone *zone, struct page *page, int low,
 		__add_to_free_list(&page[size], zone, high, migratetype, false);
 		set_buddy_order(&page[size], high);
 		nr_added += size;
+
+		/*
+		 * The parent page has been reported to the host.  The
+		 * sub-pages are part of the same reported block, so mark
+		 * them reported too.  This avoids re-reporting pages that
+		 * the host already knows about.
+		 */
+		if (reported)
+			__SetPageReported(&page[size]);
 	}
 
 	return nr_added;
@@ -1731,9 +1740,10 @@ static __always_inline void page_del_and_expand(struct zone *zone,
 						int high, int migratetype)
 {
 	int nr_pages = 1 << high;
+	bool was_reported = page_reported(page);
 
 	__del_page_from_free_list(page, zone, high, migratetype);
-	nr_pages -= expand(zone, page, low, high, migratetype);
+	nr_pages -= expand(zone, page, low, high, migratetype, was_reported);
 	account_freepages(zone, -nr_pages, migratetype);
 }
 
@@ -2300,10 +2310,12 @@ try_to_claim_block(struct zone *zone, struct page *page,
 	/* Take ownership for orders >= pageblock_order */
 	if (current_order >= pageblock_order) {
 		unsigned int nr_added;
+		bool was_reported = page_reported(page);
 
 		del_page_from_free_list(page, zone, current_order, block_type);
 		change_pageblock_range(page, current_order, start_type);
-		nr_added = expand(zone, page, order, current_order, start_type);
+		nr_added = expand(zone, page, order, current_order, start_type,
+				  was_reported);
 		account_freepages(zone, nr_added, start_type);
 		return page;
 	}
-- 
MST

[PATCH resend v6 18/30] mm: page_reporting: skip redundant zeroing of host-zeroed reported pages

[Michael S. Tsirkin]

When a guest reports free pages to the hypervisor via the page reporting
framework (used by virtio-balloon and hv_balloon), the host typically
zeros those pages when reclaiming their backing memory.  However, when
those pages are later allocated in the guest, post_alloc_hook()
unconditionally zeros them again if __GFP_ZERO is set.  This
double-zeroing is wasteful, especially for large pages.

Avoid redundant zeroing:

- Add a host_zeroes_pages flag to page_reporting_dev_info, allowing
  drivers to declare that their host zeros reported pages on reclaim.
  A static key (page_reporting_host_zeroes) gates the fast path.

- Add PG_zeroed page flag (sharing PG_private bit) to mark pages
  that have been zeroed by the host.  Set it in
  page_reporting_drain() after the host reports them.

- Thread the zeroed bool through rmqueue -> prep_new_page ->
  post_alloc_hook, where it skips redundant zeroing for __GFP_ZERO
  allocations.

No driver sets host_zeroes_pages yet; a follow-up patch to
virtio_balloon is needed to opt in.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Assisted-by: Claude:claude-opus-4-6
Assisted-by: cursor-agent:GPT-5.4-xhigh
---
 include/linux/page-flags.h     |  9 +++++
 include/linux/page_reporting.h |  3 ++
 mm/compaction.c                |  6 ++--
 mm/internal.h                  |  2 +-
 mm/page_alloc.c                | 66 +++++++++++++++++++++++-----------
 mm/page_reporting.c            | 14 +++++++-
 mm/page_reporting.h            | 12 +++++++
 7 files changed, 87 insertions(+), 25 deletions(-)

diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index 0e03d816e8b9..4ee64134acc3 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -135,6 +135,8 @@ enum pageflags {
 	PG_swapcache = PG_owner_priv_1, /* Swap page: swp_entry_t in private */
 	/* Some filesystems */
 	PG_checked = PG_owner_priv_1,
+	/* Page contents are known to be zero */
+	PG_zeroed = PG_private,
 
 	/*
 	 * Depending on the way an anonymous folio can be mapped into a page
@@ -673,6 +675,13 @@ FOLIO_TEST_CLEAR_FLAG_FALSE(young)
 FOLIO_FLAG_FALSE(idle)
 #endif
 
+/*
+ * PageZeroed() tracks pages known to be zero.  The allocator
+ * uses this to skip redundant zeroing in post_alloc_hook().
+ */
+__PAGEFLAG(Zeroed, zeroed, PF_NO_COMPOUND)
+#define __PG_ZEROED (1UL << PG_zeroed)
+
 /*
  * PageReported() is used to track reported free pages within the Buddy
  * allocator. We can use the non-atomic version of the test and set
diff --git a/include/linux/page_reporting.h b/include/linux/page_reporting.h
index 5ab5be02fa15..c331c6b36687 100644
--- a/include/linux/page_reporting.h
+++ b/include/linux/page_reporting.h
@@ -14,6 +14,9 @@ struct page_reporting_dev_info {
 	int (*report)(struct page_reporting_dev_info *prdev,
 		      struct scatterlist *sg, unsigned int nents);
 
+	/* If true, host zeros reported pages on reclaim */
+	bool host_zeroes_pages;
+
 	/* work struct for processing reports */
 	struct delayed_work work;
 
diff --git a/mm/compaction.c b/mm/compaction.c
index 72684fe81e83..0471c5326ec0 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -82,7 +82,8 @@ static inline bool is_via_compact_memory(int order) { return false; }
 
 static struct page *mark_allocated_noprof(struct page *page, unsigned int order, gfp_t gfp_flags)
 {
-	post_alloc_hook(page, order, __GFP_MOVABLE, USER_ADDR_NONE);
+	__ClearPageZeroed(page);
+	post_alloc_hook(page, order, __GFP_MOVABLE, false, USER_ADDR_NONE);
 	set_page_refcounted(page);
 	return page;
 }
@@ -1849,7 +1850,8 @@ static struct folio *compaction_alloc_noprof(struct folio *src, unsigned long da
 		set_page_private(&freepage[size], start_order);
 	}
 	dst = (struct folio *)freepage;
-	post_alloc_hook(&dst->page, order, __GFP_MOVABLE, USER_ADDR_NONE);
+	__ClearPageZeroed(&dst->page);
+	post_alloc_hook(&dst->page, order, __GFP_MOVABLE, false, USER_ADDR_NONE);
 	set_page_refcounted(&dst->page);
 	if (order)
 		prep_compound_page(&dst->page, order);
diff --git a/mm/internal.h b/mm/internal.h
index 751ae8911607..fa7ffea4d492 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -924,7 +924,7 @@ static inline void init_compound_tail(struct page *tail,
 }
 
 void post_alloc_hook(struct page *page, unsigned int order, gfp_t gfp_flags,
-		     unsigned long user_addr);
+		     bool zeroed, unsigned long user_addr);
 extern bool free_pages_prepare(struct page *page, unsigned int order);
 
 extern int user_min_free_kbytes;
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 76f39dd026ff..bd3b909cacdf 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1743,6 +1743,7 @@ static __always_inline void page_del_and_expand(struct zone *zone,
 	bool was_reported = page_reported(page);
 
 	__del_page_from_free_list(page, zone, high, migratetype);
+
 	nr_pages -= expand(zone, page, low, high, migratetype, was_reported);
 	account_freepages(zone, -nr_pages, migratetype);
 }
@@ -1815,8 +1816,10 @@ static inline bool should_skip_init(gfp_t flags)
 	return (flags & __GFP_SKIP_ZERO);
 }
 
+
 inline void post_alloc_hook(struct page *page, unsigned int order,
-				gfp_t gfp_flags, unsigned long user_addr)
+				gfp_t gfp_flags, bool zeroed,
+				unsigned long user_addr)
 {
 	bool init = !want_init_on_free() && want_init_on_alloc(gfp_flags) &&
 			!should_skip_init(gfp_flags);
@@ -1825,6 +1828,14 @@ inline void post_alloc_hook(struct page *page, unsigned int order,
 
 	set_page_private(page, 0);
 
+	/*
+	 * If the page is zeroed, skip memory initialization.
+	 * We still need to handle tag zeroing separately since the host
+	 * does not know about memory tags.
+	 */
+	if (zeroed && init && !zero_tags)
+		init = false;
+
 	arch_alloc_page(page, order);
 	debug_pagealloc_map_pages(page, 1 << order);
 
@@ -1882,13 +1893,13 @@ inline void post_alloc_hook(struct page *page, unsigned int order,
 }
 
 static void prep_new_page(struct page *page, unsigned int order, gfp_t gfp_flags,
-							unsigned int alloc_flags,
-							unsigned long user_addr)
+			  unsigned int alloc_flags, bool zeroed,
+			  unsigned long user_addr)
 {
 	if (order && (gfp_flags & __GFP_COMP))
 		prep_compound_page(page, order);
 
-	post_alloc_hook(page, order, gfp_flags, user_addr);
+	post_alloc_hook(page, order, gfp_flags, zeroed, user_addr);
 
 	/*
 	 * page is set pfmemalloc when ALLOC_NO_WATERMARKS was necessary to
@@ -3154,6 +3165,7 @@ int __isolate_free_page(struct page *page, unsigned int order)
 	}
 
 	del_page_from_free_list(page, zone, order, mt);
+	__ClearPageZeroed(page);
 
 	/*
 	 * Set the pageblock if the isolated page is at least half of a
@@ -3226,7 +3238,7 @@ static inline void zone_statistics(struct zone *preferred_zone, struct zone *z,
 static __always_inline
 struct page *rmqueue_buddy(struct zone *preferred_zone, struct zone *zone,
 			   unsigned int order, unsigned int alloc_flags,
-			   int migratetype)
+			   int migratetype, bool *zeroed)
 {
 	struct page *page;
 	unsigned long flags;
@@ -3261,6 +3273,8 @@ struct page *rmqueue_buddy(struct zone *preferred_zone, struct zone *zone,
 			}
 		}
 		spin_unlock_irqrestore(&zone->lock, flags);
+		*zeroed = PageZeroed(page);
+		__ClearPageZeroed(page);
 	} while (check_new_pages(page, order));
 
 	/*
@@ -3329,10 +3343,9 @@ static int nr_pcp_alloc(struct per_cpu_pages *pcp, struct zone *zone, int order)
 /* Remove page from the per-cpu list, caller must protect the list */
 static inline
 struct page *__rmqueue_pcplist(struct zone *zone, unsigned int order,
-			int migratetype,
-			unsigned int alloc_flags,
+			int migratetype, unsigned int alloc_flags,
 			struct per_cpu_pages *pcp,
-			struct list_head *list)
+			struct list_head *list, bool *zeroed)
 {
 	struct page *page;
 
@@ -3367,6 +3380,8 @@ struct page *__rmqueue_pcplist(struct zone *zone, unsigned int order,
 		page = list_first_entry(list, struct page, pcp_list);
 		list_del(&page->pcp_list);
 		pcp->count -= 1 << order;
+		*zeroed = PageZeroed(page);
+		__ClearPageZeroed(page);
 	} while (check_new_pages(page, order));
 
 	return page;
@@ -3375,7 +3390,8 @@ struct page *__rmqueue_pcplist(struct zone *zone, unsigned int order,
 /* Lock and remove page from the per-cpu list */
 static struct page *rmqueue_pcplist(struct zone *preferred_zone,
 			struct zone *zone, unsigned int order,
-			int migratetype, unsigned int alloc_flags)
+			int migratetype, unsigned int alloc_flags,
+			bool *zeroed)
 {
 	struct per_cpu_pages *pcp;
 	struct list_head *list;
@@ -3393,7 +3409,8 @@ static struct page *rmqueue_pcplist(struct zone *preferred_zone,
 	 */
 	pcp->free_count >>= 1;
 	list = &pcp->lists[order_to_pindex(migratetype, order)];
-	page = __rmqueue_pcplist(zone, order, migratetype, alloc_flags, pcp, list);
+	page = __rmqueue_pcplist(zone, order, migratetype, alloc_flags,
+				 pcp, list, zeroed);
 	pcp_spin_unlock(pcp);
 	if (page) {
 		__count_zid_vm_events(PGALLOC, page_zonenum(page), 1 << order);
@@ -3418,19 +3435,19 @@ static inline
 struct page *rmqueue(struct zone *preferred_zone,
 			struct zone *zone, unsigned int order,
 			gfp_t gfp_flags, unsigned int alloc_flags,
-			int migratetype)
+			int migratetype, bool *zeroed)
 {
 	struct page *page;
 
 	if (likely(pcp_allowed_order(order))) {
 		page = rmqueue_pcplist(preferred_zone, zone, order,
-				       migratetype, alloc_flags);
+				       migratetype, alloc_flags, zeroed);
 		if (likely(page))
 			goto out;
 	}
 
 	page = rmqueue_buddy(preferred_zone, zone, order, alloc_flags,
-							migratetype);
+			     migratetype, zeroed);
 
 out:
 	/* Separate test+clear to avoid unnecessary atomics */
@@ -3821,6 +3838,7 @@ get_page_from_freelist(gfp_t gfp_mask, unsigned int order, int alloc_flags,
 	struct pglist_data *last_pgdat = NULL;
 	bool last_pgdat_dirty_ok = false;
 	bool no_fallback;
+	bool zeroed;
 	bool skip_kswapd_nodes = nr_online_nodes > 1;
 	bool skipped_kswapd_nodes = false;
 
@@ -3965,10 +3983,11 @@ get_page_from_freelist(gfp_t gfp_mask, unsigned int order, int alloc_flags,
 
 try_this_zone:
 		page = rmqueue(zonelist_zone(ac->preferred_zoneref), zone, order,
-				gfp_mask, alloc_flags, ac->migratetype);
+					gfp_mask, alloc_flags, ac->migratetype,
+					&zeroed);
 		if (page) {
 			prep_new_page(page, order, gfp_mask, alloc_flags,
-				      ac->user_addr);
+				      zeroed, ac->user_addr);
 
 			return page;
 		} else {
@@ -4195,9 +4214,11 @@ __alloc_pages_direct_compact(gfp_t gfp_mask, unsigned int order,
 	count_vm_event(COMPACTSTALL);
 
 	/* Prep a captured page if available */
-	if (page)
-		prep_new_page(page, order, gfp_mask, alloc_flags,
+	if (page) {
+		__ClearPageZeroed(page);
+		prep_new_page(page, order, gfp_mask, alloc_flags, false,
 			      ac->user_addr);
+	}
 
 	/* Try get a page from the freelist if available */
 	if (!page)
@@ -5170,6 +5191,7 @@ unsigned long alloc_pages_bulk_noprof(gfp_t gfp, int preferred_nid,
 	/* Attempt the batch allocation */
 	pcp_list = &pcp->lists[order_to_pindex(ac.migratetype, 0)];
 	while (nr_populated < nr_pages) {
+		bool zeroed = false;
 
 		/* Skip existing pages */
 		if (page_array[nr_populated]) {
@@ -5178,7 +5200,7 @@ unsigned long alloc_pages_bulk_noprof(gfp_t gfp, int preferred_nid,
 		}
 
 		page = __rmqueue_pcplist(zone, 0, ac.migratetype, alloc_flags,
-								pcp, pcp_list);
+					 pcp, pcp_list, &zeroed);
 		if (unlikely(!page)) {
 			/* Try and allocate at least one page */
 			if (!nr_account) {
@@ -5189,7 +5211,7 @@ unsigned long alloc_pages_bulk_noprof(gfp_t gfp, int preferred_nid,
 		}
 		nr_account++;
 
-		prep_new_page(page, 0, gfp, 0, USER_ADDR_NONE);
+		prep_new_page(page, 0, gfp, 0, zeroed, USER_ADDR_NONE);
 		set_page_refcounted(page);
 		page_array[nr_populated++] = page;
 	}
@@ -6929,7 +6951,8 @@ static void split_free_frozen_pages(struct list_head *list, gfp_t gfp_mask)
 		list_for_each_entry_safe(page, next, &list[order], lru) {
 			int i;
 
-			post_alloc_hook(page, order, gfp_mask, USER_ADDR_NONE);
+			__ClearPageZeroed(page);
+			post_alloc_hook(page, order, gfp_mask, false, USER_ADDR_NONE);
 			if (!order)
 				continue;
 
@@ -7134,8 +7157,9 @@ int alloc_contig_frozen_range_noprof(unsigned long start, unsigned long end,
 	} else if (start == outer_start && end == outer_end && is_power_of_2(end - start)) {
 		struct page *head = pfn_to_page(start);
 
+		__ClearPageZeroed(head);
 		check_new_pages(head, order);
-		prep_new_page(head, order, gfp_mask, 0, USER_ADDR_NONE);
+		prep_new_page(head, order, gfp_mask, 0, false, USER_ADDR_NONE);
 	} else {
 		ret = -EINVAL;
 		WARN(true, "PFN range: requested [%lu, %lu), allocated [%lu, %lu)\n",
diff --git a/mm/page_reporting.c b/mm/page_reporting.c
index 006f7cdddc18..37e4fce9eb38 100644
--- a/mm/page_reporting.c
+++ b/mm/page_reporting.c
@@ -50,6 +50,8 @@ EXPORT_SYMBOL_GPL(page_reporting_order);
 #define PAGE_REPORTING_DELAY	(2 * HZ)
 static struct page_reporting_dev_info __rcu *pr_dev_info __read_mostly;
 
+DEFINE_STATIC_KEY_FALSE(page_reporting_host_zeroes);
+
 enum {
 	PAGE_REPORTING_IDLE = 0,
 	PAGE_REPORTING_REQUESTED,
@@ -129,8 +131,11 @@ page_reporting_drain(struct page_reporting_dev_info *prdev,
 		 * report on the new larger page when we make our way
 		 * up to that higher order.
 		 */
-		if (PageBuddy(page) && buddy_order(page) == order)
+		if (PageBuddy(page) && buddy_order(page) == order) {
 			__SetPageReported(page);
+			if (page_reporting_host_zeroes_pages())
+				__SetPageZeroed(page);
+		}
 	} while ((sg = sg_next(sg)));
 
 	/* reinitialize scatterlist now that it is empty */
@@ -391,6 +396,10 @@ int page_reporting_register(struct page_reporting_dev_info *prdev)
 	/* Assign device to allow notifications */
 	rcu_assign_pointer(pr_dev_info, prdev);
 
+	/* enable zeroed page optimization if host zeroes reported pages */
+	if (prdev->host_zeroes_pages)
+		static_branch_enable(&page_reporting_host_zeroes);
+
 	/* enable page reporting notification */
 	if (!static_key_enabled(&page_reporting_enabled)) {
 		static_branch_enable(&page_reporting_enabled);
@@ -415,6 +424,9 @@ void page_reporting_unregister(struct page_reporting_dev_info *prdev)
 
 		/* Flush any existing work, and lock it out */
 		cancel_delayed_work_sync(&prdev->work);
+
+		if (prdev->host_zeroes_pages)
+			static_branch_disable(&page_reporting_host_zeroes);
 	}
 
 	mutex_unlock(&page_reporting_mutex);
diff --git a/mm/page_reporting.h b/mm/page_reporting.h
index c51dbc228b94..736ea7b37e9e 100644
--- a/mm/page_reporting.h
+++ b/mm/page_reporting.h
@@ -15,6 +15,13 @@ DECLARE_STATIC_KEY_FALSE(page_reporting_enabled);
 extern unsigned int page_reporting_order;
 void __page_reporting_notify(void);
 
+DECLARE_STATIC_KEY_FALSE(page_reporting_host_zeroes);
+
+static inline bool page_reporting_host_zeroes_pages(void)
+{
+	return static_branch_unlikely(&page_reporting_host_zeroes);
+}
+
 static inline bool page_reported(struct page *page)
 {
 	return static_branch_unlikely(&page_reporting_enabled) &&
@@ -46,6 +53,11 @@ static inline void page_reporting_notify_free(unsigned int order)
 #else /* CONFIG_PAGE_REPORTING */
 #define page_reported(_page)	false
 
+static inline bool page_reporting_host_zeroes_pages(void)
+{
+	return false;
+}
+
 static inline void page_reporting_notify_free(unsigned int order)
 {
 }
-- 
MST

[PATCH resend v6 19/30] mm: page_reporting: add per-page zeroed bitmap for host feedback

[Michael S. Tsirkin]

The host may skip zeroing some reported pages (e.g., due to alignment
constraints or bounce buffer fallback in QEMU).  Currently, when
host_zeroes_pages is set, all reported pages are unconditionally
marked PG_zeroed - even ones the host did not actually zero.

Add a zeroed_bitmap to page_reporting_dev_info that the report()
callback can use to indicate which pages were actually zeroed.
The driver's report() callback is responsible for managing the
bitmap: zeroing it before sending pages to the host, then setting
bits for pages the host actually zeroed.

page_reporting_drain() checks the bitmap per-page in addition to the
global host_zeroes_pages flag.

No driver sets host_zeroes_pages yet, so the static key is
off and the bitmap is never read.  Behavior is unchanged.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Assisted-by: Claude:claude-opus-4-6
Assisted-by: cursor-agent:GPT-5.4-xhigh
---
 include/linux/page_reporting.h | 7 +++++++
 mm/page_reporting.c            | 8 ++++++--
 2 files changed, 13 insertions(+), 2 deletions(-)

diff --git a/include/linux/page_reporting.h b/include/linux/page_reporting.h
index c331c6b36687..e2e6a487ddab 100644
--- a/include/linux/page_reporting.h
+++ b/include/linux/page_reporting.h
@@ -17,6 +17,13 @@ struct page_reporting_dev_info {
 	/* If true, host zeros reported pages on reclaim */
 	bool host_zeroes_pages;
 
+	/*
+	 * Per-page zeroed status, indexed by scatterlist position.
+	 * The driver's report() callback must clear the bitmap,
+	 * then set bits for pages that were actually zeroed.
+	 */
+	DECLARE_BITMAP(zeroed_bitmap, PAGE_REPORTING_CAPACITY);
+
 	/* work struct for processing reports */
 	struct delayed_work work;
 
diff --git a/mm/page_reporting.c b/mm/page_reporting.c
index 37e4fce9eb38..6c957a9daeef 100644
--- a/mm/page_reporting.c
+++ b/mm/page_reporting.c
@@ -108,6 +108,7 @@ page_reporting_drain(struct page_reporting_dev_info *prdev,
 		     struct scatterlist *sgl, unsigned int nents, bool reported)
 {
 	struct scatterlist *sg = sgl;
+	unsigned int i = 0;
 
 	/*
 	 * Drain the now reported pages back into their respective
@@ -122,7 +123,7 @@ page_reporting_drain(struct page_reporting_dev_info *prdev,
 
 		/* If the pages were not reported due to error skip flagging */
 		if (!reported)
-			continue;
+			goto next;
 
 		/*
 		 * If page was not commingled with another page we can
@@ -133,9 +134,12 @@ page_reporting_drain(struct page_reporting_dev_info *prdev,
 		 */
 		if (PageBuddy(page) && buddy_order(page) == order) {
 			__SetPageReported(page);
-			if (page_reporting_host_zeroes_pages())
+			if (page_reporting_host_zeroes_pages() &&
+			    test_bit(i, prdev->zeroed_bitmap))
 				__SetPageZeroed(page);
 		}
+next:
+		i++;
 	} while ((sg = sg_next(sg)));
 
 	/* reinitialize scatterlist now that it is empty */
-- 
MST

[PATCH resend v6 20/30] mm: page_alloc: clear PG_zeroed on buddy merge if not both zero

[Michael S. Tsirkin]

When two buddy pages merge in __free_one_page(), preserve
PG_zeroed on the merged page only if both buddies have the
flag set.  Otherwise clear it.

The merged page would inherit PG_zeroed, and a later __GFP_ZERO
allocation would skip zeroing stale data in the non-zero half.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Assisted-by: Claude:claude-opus-4-6
Assisted-by: cursor-agent:GPT-5.4-xhigh
---
 mm/page_alloc.c | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index bd3b909cacdf..d70c9ba6b329 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -940,10 +940,14 @@ static inline void __free_one_page(struct page *page,
 	unsigned long buddy_pfn = 0;
 	unsigned long combined_pfn;
 	struct page *buddy;
+	bool buddy_zeroed;
+	bool page_zeroed;
 	bool to_tail;
 
 	VM_BUG_ON(!zone_is_initialized(zone));
-	VM_BUG_ON_PAGE(page->flags.f & PAGE_FLAGS_CHECK_AT_PREP, page);
+	/* PG_zeroed (aliased to PG_private) is valid on free-list pages */
+	VM_BUG_ON_PAGE(page->flags.f &
+		       (PAGE_FLAGS_CHECK_AT_PREP & ~__PG_ZEROED), page);
 
 	VM_BUG_ON(migratetype == -1);
 	VM_BUG_ON_PAGE(pfn & ((1 << order) - 1), page);
@@ -978,6 +982,8 @@ static inline void __free_one_page(struct page *page,
 				goto done_merging;
 		}
 
+		buddy_zeroed = PageZeroed(buddy);
+
 		/*
 		 * Our buddy is free or it is CONFIG_DEBUG_PAGEALLOC guard page,
 		 * merge with it and move up one order.
@@ -996,10 +1002,17 @@ static inline void __free_one_page(struct page *page,
 			change_pageblock_range(buddy, order, migratetype);
 		}
 
+		page_zeroed = PageZeroed(page);
+		__ClearPageZeroed(page);
+		__ClearPageZeroed(buddy);
+
 		combined_pfn = buddy_pfn & pfn;
 		page = page + (combined_pfn - pfn);
 		pfn = combined_pfn;
 		order++;
+
+		if (page_zeroed && buddy_zeroed)
+			__SetPageZeroed(page);
 	}
 
 done_merging:
-- 
MST

[PATCH resend v6 21/30] mm: page_alloc: preserve PG_zeroed in page_del_and_expand

[Michael S. Tsirkin]

Propagate PG_zeroed through buddy splits in page_del_and_expand()
and try_to_claim_block().  When a zeroed high-order page is split
to satisfy a smaller allocation, the sub-pages placed back on the
free lists keep PG_zeroed.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Assisted-by: Claude:claude-opus-4-6
Assisted-by: cursor-agent:GPT-5.4-xhigh
---
 mm/page_alloc.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index d70c9ba6b329..468e8bde7d34 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1712,7 +1712,8 @@ struct page *__pageblock_pfn_to_page(unsigned long start_pfn,
  * -- nyc
  */
 static inline unsigned int expand(struct zone *zone, struct page *page, int low,
-				  int high, int migratetype, bool reported)
+				  int high, int migratetype, bool reported,
+				  bool zeroed)
 {
 	unsigned int size = 1 << high;
 	unsigned int nr_added = 0;
@@ -1743,6 +1744,8 @@ static inline unsigned int expand(struct zone *zone, struct page *page, int low,
 		 */
 		if (reported)
 			__SetPageReported(&page[size]);
+		if (zeroed)
+			__SetPageZeroed(&page[size]);
 	}
 
 	return nr_added;
@@ -1754,10 +1757,12 @@ static __always_inline void page_del_and_expand(struct zone *zone,
 {
 	int nr_pages = 1 << high;
 	bool was_reported = page_reported(page);
+	bool was_zeroed = PageZeroed(page);
 
 	__del_page_from_free_list(page, zone, high, migratetype);
 
-	nr_pages -= expand(zone, page, low, high, migratetype, was_reported);
+	nr_pages -= expand(zone, page, low, high, migratetype, was_reported,
+			   was_zeroed);
 	account_freepages(zone, -nr_pages, migratetype);
 }
 
@@ -2335,11 +2340,12 @@ try_to_claim_block(struct zone *zone, struct page *page,
 	if (current_order >= pageblock_order) {
 		unsigned int nr_added;
 		bool was_reported = page_reported(page);
+		bool was_zeroed = PageZeroed(page);
 
 		del_page_from_free_list(page, zone, current_order, block_type);
 		change_pageblock_range(page, current_order, start_type);
 		nr_added = expand(zone, page, order, current_order, start_type,
-				  was_reported);
+				  was_reported, was_zeroed);
 		account_freepages(zone, nr_added, start_type);
 		return page;
 	}
-- 
MST

[PATCH resend v6 22/30] virtio_balloon: submit reported pages as individual buffers

[Michael S. Tsirkin]

Submit each reported page as a separate virtqueue buffer instead
of one buffer with an sg list of all pages. This avoids indirect
descriptor allocation (kmalloc in the reporting path) and gives
per-page used length feedback from the device.

On error, the already-queued pages are kicked and drained
before the error is returned. The caller (page_reporting_drain)
then marks the batch as unreported, which is conservative
but correct.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Assisted-by: Claude:claude-opus-4-6
---
 drivers/virtio/virtio_balloon.c | 36 +++++++++++++++++++++------------
 1 file changed, 23 insertions(+), 13 deletions(-)

diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
index 6a1a610c2cb1..fdfd828657dd 100644
--- a/drivers/virtio/virtio_balloon.c
+++ b/drivers/virtio/virtio_balloon.c
@@ -202,25 +202,35 @@ static int virtballoon_free_page_report(struct page_reporting_dev_info *pr_dev_i
 	struct virtio_balloon *vb =
 		container_of(pr_dev_info, struct virtio_balloon, pr_dev_info);
 	struct virtqueue *vq = vb->reporting_vq;
-	unsigned int unused, err;
+	unsigned int i, err;
 
 	/* We should always be able to add these buffers to an empty queue. */
-	err = virtqueue_add_inbuf(vq, sg, nents, vb, GFP_NOWAIT);
+	for (i = 0; i < nents; i++) {
+		struct scatterlist one;
 
-	/*
-	 * In the extremely unlikely case that something has occurred and we
-	 * are able to trigger an error we will simply display a warning
-	 * and exit without actually processing the pages.
-	 */
-	if (WARN_ON_ONCE(err))
-		return err;
+		sg_init_table(&one, 1);
+		sg_set_page(&one, sg_page(&sg[i]), sg[i].length,
+			    sg[i].offset);
+		err = virtqueue_add_inbuf(vq, &one, 1, &sg[i], GFP_NOWAIT);
+		if (WARN_ON_ONCE(err)) {
+			nents = i;
+			break;
+		}
+	}
 
-	virtqueue_kick(vq);
+	if (nents) {
+		virtqueue_kick(vq);
 
-	/* When host has read buffer, this completes via balloon_ack */
-	wait_event(vb->acked, virtqueue_get_buf(vq, &unused));
+		/* When host has read buffer, this completes via balloon_ack */
+		for (i = 0; i < nents; i++) {
+			unsigned int unused;
 
-	return 0;
+			wait_event(vb->acked,
+				   virtqueue_get_buf(vq, &unused));
+		}
+	}
+
+	return err;
 }
 
 static void set_page_pfns(struct virtio_balloon *vb,
-- 
MST

[PATCH resend v6 23/30] mm: page_reporting: add flush parameter with page budget

[Michael S. Tsirkin]

Add a write-only module parameter 'flush' that triggers immediate
page reporting.  The value specifies a page budget: at least
this many pages (at page_reporting_order) will be reported,
or all unreported pages if fewer remain.  The actual number
reported may exceed the budget since each reporting pass
processes a full cycle across all zones.

This is helpful when there is a lot of memory freed quickly,
and a single cycle may not process all free pages due to
internal budget limits.

  echo 512 > /sys/module/page_reporting/parameters/flush

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Assisted-by: Claude:claude-opus-4-6
Assisted-by: cursor-agent:GPT-5.4-xhigh
---
 mm/page_reporting.c | 42 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 42 insertions(+)

diff --git a/mm/page_reporting.c b/mm/page_reporting.c
index 6c957a9daeef..f4a0e27ac7fb 100644
--- a/mm/page_reporting.c
+++ b/mm/page_reporting.c
@@ -358,6 +358,48 @@ static void page_reporting_process(struct work_struct *work)
 static DEFINE_MUTEX(page_reporting_mutex);
 DEFINE_STATIC_KEY_FALSE(page_reporting_enabled);
 
+static int page_reporting_flush_set(const char *val,
+				    const struct kernel_param *kp)
+{
+	struct page_reporting_dev_info *prdev;
+	unsigned int budget;
+	int err;
+
+	err = kstrtouint(val, 0, &budget);
+	if (err)
+		return err;
+	if (!budget)
+		return 0;
+
+	mutex_lock(&page_reporting_mutex);
+	prdev = rcu_dereference_protected(pr_dev_info,
+				lockdep_is_held(&page_reporting_mutex));
+	if (prdev) {
+		unsigned int reported;
+
+		for (reported = 0; reported < budget;
+		     reported += prdev->capacity) {
+			flush_delayed_work(&prdev->work);
+			__page_reporting_request(prdev);
+			flush_delayed_work(&prdev->work);
+			if (atomic_read(&prdev->state) == PAGE_REPORTING_IDLE)
+				break;
+			if (signal_pending(current))
+				break;
+		}
+	}
+	mutex_unlock(&page_reporting_mutex);
+	return 0;
+}
+
+static const struct kernel_param_ops flush_ops = {
+	.set = page_reporting_flush_set,
+	.get = param_get_uint,
+};
+static unsigned int page_reporting_flush;
+module_param_cb(flush, &flush_ops, &page_reporting_flush, 0200);
+MODULE_PARM_DESC(flush, "Report at least N pages at page_reporting_order, or until all reported");
+
 int page_reporting_register(struct page_reporting_dev_info *prdev)
 {
 	int err = 0;
-- 
MST

[PATCH resend v6 24/30] mm: page_alloc: propagate PG_zeroed in split_large_buddy

[Michael S. Tsirkin]

When splitting a large buddy page, propagate the PG_zeroed flag
to each sub-page before freeing it.  __free_pages_prepare clears
all flags (including PG_zeroed), so the flag must be re-set on
each fragment after the split.  This ensures that the buddy merge
logic can see PG_zeroed on pages that were part of a larger
zeroed block.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Assisted-by: Claude:claude-opus-4-6
Assisted-by: cursor-agent:GPT-5.4-xhigh
---
 mm/page_alloc.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 468e8bde7d34..ce43f5a3dbaa 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1523,6 +1523,7 @@ static void split_large_buddy(struct zone *zone, struct page *page,
 			      unsigned long pfn, int order, fpi_t fpi)
 {
 	unsigned long end = pfn + (1 << order);
+	bool zeroed = PageZeroed(page);
 
 	VM_WARN_ON_ONCE(!IS_ALIGNED(pfn, 1 << order));
 	/* Caller removed page from freelist, buddy info cleared! */
@@ -1534,6 +1535,8 @@ static void split_large_buddy(struct zone *zone, struct page *page,
 	do {
 		int mt = get_pfnblock_migratetype(page, pfn);
 
+		if (zeroed)
+			__SetPageZeroed(page);
 		__free_one_page(page, pfn, zone, order, mt, fpi);
 		pfn += 1 << order;
 		if (pfn == end)
-- 
MST

[PATCH resend v6 25/30] virtio_balloon: skip zeroing for host-zeroed reported pages

[Michael S. Tsirkin]

Implement VIRTIO_BALLOON_F_DEVICE_INIT_REPORTED (per virtio spec
proposal): when negotiated, the device initializes reported pages
(zeros, or poison_val if PAGE_POISON).

Check per-page used length returned by the device to determine
which reported pages were zeroed. If used_len matches the page
size, the device successfully initialized the page (e.g. via
MADV_DONTNEED), and we set the corresponding zeroed_bitmap bit.

Gate host_zeroes_pages on the feature bit and page content:
when PAGE_POISON is negotiated with non-zero poison_val, the
device fills with poison not zeros, so pages are not zeroed.

Clear the feature in validate() if REPORTING is not present
or if PAGE_POISON is active with non-zero poison_val.

See the virtio spec change:
https://github.com/oasis-tcs/virtio-spec/issues/244

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Assisted-by: Claude:claude-opus-4-6
Assisted-by: cursor-agent:GPT-5.4-xhigh
---
 drivers/virtio/virtio_balloon.c     | 22 ++++++++++++++++++++--
 include/uapi/linux/virtio_balloon.h |  1 +
 2 files changed, 21 insertions(+), 2 deletions(-)

diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
index fdfd828657dd..e5d11782ce41 100644
--- a/drivers/virtio/virtio_balloon.c
+++ b/drivers/virtio/virtio_balloon.c
@@ -204,6 +204,8 @@ static int virtballoon_free_page_report(struct page_reporting_dev_info *pr_dev_i
 	struct virtqueue *vq = vb->reporting_vq;
 	unsigned int i, err;
 
+	bitmap_zero(pr_dev_info->zeroed_bitmap, nents);
+
 	/* We should always be able to add these buffers to an empty queue. */
 	for (i = 0; i < nents; i++) {
 		struct scatterlist one;
@@ -223,10 +225,14 @@ static int virtballoon_free_page_report(struct page_reporting_dev_info *pr_dev_i
 
 		/* When host has read buffer, this completes via balloon_ack */
 		for (i = 0; i < nents; i++) {
-			unsigned int unused;
+			struct scatterlist *entry;
+			unsigned int used_len;
 
 			wait_event(vb->acked,
-				   virtqueue_get_buf(vq, &unused));
+				   (entry = virtqueue_get_buf(vq, &used_len)));
+			if (used_len == entry->length)
+				set_bit(entry - sg,
+					pr_dev_info->zeroed_bitmap);
 		}
 	}
 
@@ -1048,6 +1054,9 @@ static int virtballoon_probe(struct virtio_device *vdev)
 #endif
 
 		vb->pr_dev_info.capacity = capacity;
+		vb->pr_dev_info.host_zeroes_pages =
+			virtio_has_feature(vdev,
+					   VIRTIO_BALLOON_F_DEVICE_INIT_REPORTED);
 		err = page_reporting_register(&vb->pr_dev_info);
 		if (err)
 			goto out_unregister_oom;
@@ -1173,6 +1182,14 @@ static int virtballoon_validate(struct virtio_device *vdev)
 	else if (!virtio_has_feature(vdev, VIRTIO_BALLOON_F_PAGE_POISON))
 		__virtio_clear_bit(vdev, VIRTIO_BALLOON_F_REPORTING);
 
+	if (!virtio_has_feature(vdev, VIRTIO_BALLOON_F_REPORTING))
+		__virtio_clear_bit(vdev, VIRTIO_BALLOON_F_DEVICE_INIT_REPORTED);
+
+	/* Device fills with poison_val, not zeros; disable zeroed hint */
+	if (virtio_has_feature(vdev, VIRTIO_BALLOON_F_PAGE_POISON) &&
+	    !want_init_on_free())
+		__virtio_clear_bit(vdev, VIRTIO_BALLOON_F_DEVICE_INIT_REPORTED);
+
 	__virtio_clear_bit(vdev, VIRTIO_F_ACCESS_PLATFORM);
 	return 0;
 }
@@ -1184,6 +1201,7 @@ static unsigned int features[] = {
 	VIRTIO_BALLOON_F_FREE_PAGE_HINT,
 	VIRTIO_BALLOON_F_PAGE_POISON,
 	VIRTIO_BALLOON_F_REPORTING,
+	VIRTIO_BALLOON_F_DEVICE_INIT_REPORTED,
 };
 
 static struct virtio_driver virtio_balloon_driver = {
diff --git a/include/uapi/linux/virtio_balloon.h b/include/uapi/linux/virtio_balloon.h
index ee35a372805d..13074631f300 100644
--- a/include/uapi/linux/virtio_balloon.h
+++ b/include/uapi/linux/virtio_balloon.h
@@ -37,6 +37,7 @@
 #define VIRTIO_BALLOON_F_FREE_PAGE_HINT	3 /* VQ to report free pages */
 #define VIRTIO_BALLOON_F_PAGE_POISON	4 /* Guest is using page poisoning */
 #define VIRTIO_BALLOON_F_REPORTING	5 /* Page reporting virtqueue */
+#define VIRTIO_BALLOON_F_DEVICE_INIT_REPORTED	6 /* Device initializes reported pages */
 
 /* Size of a PFN in the balloon interface. */
 #define VIRTIO_BALLOON_PFN_SHIFT 12
-- 
MST

[PATCH resend v6 26/30] virtio_balloon: disable reporting zeroed optimization for confidential guests

[Michael S. Tsirkin]

In confidential computing environments (TDX, SEV-SNP), the host
is untrusted and may lie about zeroing reported pages. Clear
DEVICE_INIT_REPORTED in validate() so the guest does not skip
re-zeroing based on hints from an untrusted device.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Assisted-by: Claude:claude-opus-4-6
Assisted-by: cursor-agent:GPT-5.4-xhigh
---
 drivers/virtio/virtio_balloon.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
index e5d11782ce41..d1cdb904d60b 100644
--- a/drivers/virtio/virtio_balloon.c
+++ b/drivers/virtio/virtio_balloon.c
@@ -18,6 +18,7 @@
 #include <linux/wait.h>
 #include <linux/mm.h>
 #include <linux/page_reporting.h>
+#include <linux/cc_platform.h>
 
 /*
  * Balloon device works in 4K page units.  So each page is pointed to by
@@ -1190,6 +1191,8 @@ static int virtballoon_validate(struct virtio_device *vdev)
 	    !want_init_on_free())
 		__virtio_clear_bit(vdev, VIRTIO_BALLOON_F_DEVICE_INIT_REPORTED);
 
+	if (cc_platform_has(CC_ATTR_GUEST_MEM_ENCRYPT))
+		__virtio_clear_bit(vdev, VIRTIO_BALLOON_F_DEVICE_INIT_REPORTED);
 	__virtio_clear_bit(vdev, VIRTIO_F_ACCESS_PLATFORM);
 	return 0;
 }
-- 
MST

[PATCH resend v6 27/30] mm: add free_frozen_pages_zeroed

[Michael S. Tsirkin]

Add free_frozen_pages_zeroed(page, order) to free a frozen page
while marking it as zeroed, so the next allocation can skip
redundant zeroing.

An FPI_ZEROED internal flag carries the hint through the free path.
PageZeroed is set after __free_pages_prepare() clears all flags,
so the hint survives on the free list.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Assisted-by: Claude:claude-opus-4-6
---
 include/linux/gfp.h |  1 +
 mm/internal.h       |  1 -
 mm/page_alloc.c     | 21 ++++++++++++++++++++-
 3 files changed, 21 insertions(+), 2 deletions(-)

diff --git a/include/linux/gfp.h b/include/linux/gfp.h
index ee35c5367abc..e0d5743de68d 100644
--- a/include/linux/gfp.h
+++ b/include/linux/gfp.h
@@ -384,6 +384,7 @@ __meminit void *alloc_pages_exact_nid_noprof(int nid, size_t size, gfp_t gfp_mas
 extern void __free_pages(struct page *page, unsigned int order);
 extern void free_pages_nolock(struct page *page, unsigned int order);
 extern void free_pages(unsigned long addr, unsigned int order);
+void free_frozen_pages_zeroed(struct page *page, unsigned int order);
 
 #define __free_page(page) __free_pages((page), 0)
 #define free_page(addr) free_pages((addr), 0)
diff --git a/mm/internal.h b/mm/internal.h
index fa7ffea4d492..0ef6f8221e5c 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -934,7 +934,6 @@ struct page *__alloc_frozen_pages_noprof(gfp_t, unsigned int order, int nid,
 #define __alloc_frozen_pages(...) \
 	alloc_hooks(__alloc_frozen_pages_noprof(__VA_ARGS__))
 void free_frozen_pages(struct page *page, unsigned int order);
-void free_frozen_pages_zeroed(struct page *page, unsigned int order);
 void free_unref_folios(struct folio_batch *fbatch);
 
 #ifdef CONFIG_NUMA
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index ce43f5a3dbaa..8eebe01cda80 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -90,6 +90,13 @@ typedef int __bitwise fpi_t;
 /* Free the page without taking locks. Rely on trylock only. */
 #define FPI_TRYLOCK		((__force fpi_t)BIT(2))
 
+/*
+ * The page contents are known to be zero (e.g., the host zeroed them
+ * during balloon deflate).  Set PageZeroed after free so the next
+ * allocation can skip redundant zeroing.
+ */
+#define FPI_ZEROED		((__force fpi_t)BIT(3))
+
 /* prevent >1 _updater_ of zone percpu pageset ->high and ->batch fields */
 static DEFINE_MUTEX(pcp_batch_high_lock);
 #define MIN_PERCPU_PAGELIST_HIGH_FRACTION (8)
@@ -1596,8 +1603,11 @@ static void __free_pages_ok(struct page *page, unsigned int order,
 	unsigned long pfn = page_to_pfn(page);
 	struct zone *zone = page_zone(page);
 
-	if (__free_pages_prepare(page, order, fpi_flags))
+	if (__free_pages_prepare(page, order, fpi_flags)) {
+		if (fpi_flags & FPI_ZEROED)
+			__SetPageZeroed(page);
 		free_one_page(zone, page, pfn, order, fpi_flags);
+	}
 }
 
 void __meminit __free_pages_core(struct page *page, unsigned int order,
@@ -3000,6 +3010,9 @@ static void __free_frozen_pages(struct page *page, unsigned int order,
 	if (!__free_pages_prepare(page, order, fpi_flags))
 		return;
 
+	if (fpi_flags & FPI_ZEROED)
+		__SetPageZeroed(page);
+
 	/*
 	 * We only track unmovable, reclaimable and movable on pcp lists.
 	 * Place ISOLATE pages on the isolated list because they are being
@@ -3038,6 +3051,12 @@ void free_frozen_pages(struct page *page, unsigned int order)
 	__free_frozen_pages(page, order, FPI_NONE);
 }
 
+void free_frozen_pages_zeroed(struct page *page, unsigned int order)
+{
+	__free_frozen_pages(page, order, FPI_ZEROED);
+}
+EXPORT_SYMBOL(free_frozen_pages_zeroed);
+
 void free_frozen_pages_nolock(struct page *page, unsigned int order)
 {
 	__free_frozen_pages(page, order, FPI_TRYLOCK);
-- 
MST

[PATCH resend v6 28/30] mm: add put_page_zeroed and folio_put_zeroed

[Michael S. Tsirkin]

Add put_page_zeroed() / folio_put_zeroed() for callers that hold
a reference to a page known to be zeroed.

If this drops the last reference, the page goes through
__folio_put_zeroed() which calls free_frozen_pages_zeroed() so
the zeroed hint is preserved.  If someone else still holds a
reference, the hint is simply lost - this is best-effort.

This is useful for balloon drivers during deflation: the host
has already zeroed the pages, and the balloon is typically the
sole owner.  But if the page happens to be shared, silently
dropping the hint is safe and avoids the need for callers to
check the refcount.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Assisted-by: Claude:claude-opus-4-6
---
 include/linux/mm.h | 12 ++++++++++++
 mm/swap.c          | 18 ++++++++++++++++--
 2 files changed, 28 insertions(+), 2 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 3b1ca90fd435..4c51b7bd7576 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1913,6 +1913,7 @@ static inline struct folio *virt_to_folio(const void *x)
 }
 
 void __folio_put(struct folio *folio);
+void __folio_put_zeroed(struct folio *folio);
 
 void split_page(struct page *page, unsigned int order);
 void folio_copy(struct folio *dst, struct folio *src);
@@ -2090,6 +2091,17 @@ static inline void folio_put(struct folio *folio)
 		__folio_put(folio);
 }
 
+static inline void folio_put_zeroed(struct folio *folio)
+{
+	if (folio_put_testzero(folio))
+		__folio_put_zeroed(folio);
+}
+
+static inline void put_page_zeroed(struct page *page)
+{
+	folio_put_zeroed(page_folio(page));
+}
+
 /**
  * folio_put_refs - Reduce the reference count on a folio.
  * @folio: The folio.
diff --git a/mm/swap.c b/mm/swap.c
index 5cc44f0de987..8d57223dfe34 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -94,7 +94,7 @@ static void page_cache_release(struct folio *folio)
 		lruvec_unlock_irqrestore(lruvec, flags);
 }
 
-void __folio_put(struct folio *folio)
+static void ___folio_put(struct folio *folio, bool zeroed)
 {
 	if (unlikely(folio_is_zone_device(folio))) {
 		free_zone_device_folio(folio);
@@ -109,10 +109,24 @@ void __folio_put(struct folio *folio)
 	page_cache_release(folio);
 	folio_unqueue_deferred_split(folio);
 	mem_cgroup_uncharge(folio);
-	free_frozen_pages(&folio->page, folio_order(folio));
+	if (zeroed)
+		free_frozen_pages_zeroed(&folio->page, folio_order(folio));
+	else
+		free_frozen_pages(&folio->page, folio_order(folio));
+}
+
+void __folio_put(struct folio *folio)
+{
+	___folio_put(folio, false);
 }
 EXPORT_SYMBOL(__folio_put);
 
+void __folio_put_zeroed(struct folio *folio)
+{
+	___folio_put(folio, true);
+}
+EXPORT_SYMBOL(__folio_put_zeroed);
+
 typedef void (*move_fn_t)(struct lruvec *lruvec, struct folio *folio);
 
 static void lru_add(struct lruvec *lruvec, struct folio *folio)
-- 
MST

[PATCH resend v6 29/30] virtio_balloon: implement VIRTIO_BALLOON_F_DEVICE_INIT_ON_INFLATE

[Michael S. Tsirkin]

When the device offers DEVICE_INIT_ON_INFLATE (bit 7), the device
initializes inflated pages and returns a per-page bitmap indicating
which pages were successfully initialized.

The driver appends a device-writable bitmap buffer to each inflate
descriptor chain via virtqueue_add_sgs. After the host acknowledges,
the driver checks bitmap bits (bounded by used_len) and marks pages
with SetPageZeroed.

tell_host() returns used_len from virtqueue_get_buf(). Bitmap reads
are bounded: fill_balloon() and virtballoon_migratepage() only trust
bits within the used_len range.

On deflate, release_pages_balloon checks PageZeroed per page and
uses put_page_zeroed for pages the host initialized, propagating
the zeroed hint to the buddy allocator.

If inflate_vq has fewer than 2 descriptors, probe fails with
-ENOSPC. If PAGE_POISON is negotiated with non-zero poison_val,
the feature is cleared in validate().

See the virtio spec change:
https://lore.kernel.org/all/9c69b992c3dd83dfef3db92cd86b2fd8a0730d48.1777731396.git.mst@redhat.com

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Assisted-by: Claude:claude-opus-4-6
Assisted-by: cursor-agent:GPT-5.4-xhigh
---
 drivers/virtio/virtio_balloon.c     | 102 ++++++++++++++++++++++++----
 include/uapi/linux/virtio_balloon.h |   1 +
 2 files changed, 90 insertions(+), 13 deletions(-)

diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
index d1cdb904d60b..284108dbcff1 100644
--- a/drivers/virtio/virtio_balloon.c
+++ b/drivers/virtio/virtio_balloon.c
@@ -121,6 +121,9 @@ struct virtio_balloon {
 	struct virtqueue *reporting_vq;
 	struct page_reporting_dev_info pr_dev_info;
 
+	/* Bitmap returned by host for DEVICE_INIT_ON_INFLATE */
+	DECLARE_BITMAP(inflate_bitmap, VIRTIO_BALLOON_ARRAY_PFNS_MAX);
+
 	/* State for keeping the wakeup_source active while adjusting the balloon */
 	spinlock_t wakeup_lock;
 	bool processing_wakeup_event;
@@ -181,20 +184,30 @@ static void balloon_ack(struct virtqueue *vq)
 	wake_up(&vb->acked);
 }
 
-static void tell_host(struct virtio_balloon *vb, struct virtqueue *vq)
+static unsigned int tell_host(struct virtio_balloon *vb, struct virtqueue *vq)
 {
-	struct scatterlist sg;
+	struct scatterlist sg_out, sg_in;
+	struct scatterlist *sgs[] = { &sg_out, &sg_in };
 	unsigned int len;
 
-	sg_init_one(&sg, vb->pfns, sizeof(vb->pfns[0]) * vb->num_pfns);
+	sg_init_one(&sg_out, vb->pfns, sizeof(vb->pfns[0]) * vb->num_pfns);
 
-	/* We should always be able to add one buffer to an empty queue. */
-	virtqueue_add_outbuf(vq, &sg, 1, vb, GFP_KERNEL);
+	if (vq == vb->inflate_vq &&
+	    virtio_has_feature(vb->vdev,
+			       VIRTIO_BALLOON_F_DEVICE_INIT_ON_INFLATE)) {
+		unsigned int bitmap_bytes;
+
+		bitmap_bytes = DIV_ROUND_UP(vb->num_pfns, 8);
+		bitmap_zero(vb->inflate_bitmap, vb->num_pfns);
+		sg_init_one(&sg_in, vb->inflate_bitmap, bitmap_bytes);
+		virtqueue_add_sgs(vq, sgs, 1, 1, vb, GFP_KERNEL);
+	} else {
+		virtqueue_add_outbuf(vq, &sg_out, 1, vb, GFP_KERNEL);
+	}
 	virtqueue_kick(vq);
 
-	/* When host has read buffer, this completes via balloon_ack */
 	wait_event(vb->acked, virtqueue_get_buf(vq, &len));
-
+	return len;
 }
 
 static int virtballoon_free_page_report(struct page_reporting_dev_info *pr_dev_info,
@@ -297,8 +310,37 @@ static unsigned int fill_balloon(struct virtio_balloon *vb, size_t num)
 
 	num_allocated_pages = vb->num_pfns;
 	/* Did we get any? */
-	if (vb->num_pfns != 0)
-		tell_host(vb, vb->inflate_vq);
+	if (vb->num_pfns != 0) {
+		unsigned int used_len = tell_host(vb, vb->inflate_vq);
+
+		if (virtio_has_feature(vb->vdev,
+				       VIRTIO_BALLOON_F_DEVICE_INIT_ON_INFLATE)) {
+			unsigned int i;
+			unsigned int valid_bits = used_len * 8;
+
+			for (i = 0; i < vb->num_pfns;
+			     i += VIRTIO_BALLOON_PAGES_PER_PAGE) {
+				unsigned int pfn, j;
+				bool zeroed = true;
+
+				if (i + VIRTIO_BALLOON_PAGES_PER_PAGE > valid_bits)
+					break;
+				for (j = 0; j < VIRTIO_BALLOON_PAGES_PER_PAGE; j++) {
+					if (!test_bit(i + j, vb->inflate_bitmap)) {
+						zeroed = false;
+						break;
+					}
+				}
+				if (zeroed) {
+					pfn = virtio32_to_cpu(vb->vdev,
+							      vb->pfns[i]);
+					__SetPageZeroed(pfn_to_page(pfn >>
+						(PAGE_SHIFT -
+						 VIRTIO_BALLOON_PFN_SHIFT)));
+				}
+			}
+		}
+	}
 	mutex_unlock(&vb->balloon_lock);
 
 	return num_allocated_pages;
@@ -311,7 +353,12 @@ static void release_pages_balloon(struct virtio_balloon *vb,
 
 	list_for_each_entry_safe(page, next, pages, lru) {
 		list_del(&page->lru);
-		put_page(page); /* balloon reference */
+		if (PageZeroed(page)) {
+			__ClearPageZeroed(page);
+			put_page_zeroed(page);
+		} else {
+			put_page(page);
+		}
 	}
 }
 
@@ -858,7 +905,25 @@ static int virtballoon_migratepage(struct balloon_dev_info *vb_dev_info,
 	/* balloon's page migration 1st step  -- inflate "newpage" */
 	vb->num_pfns = VIRTIO_BALLOON_PAGES_PER_PAGE;
 	set_page_pfns(vb, vb->pfns, newpage);
-	tell_host(vb, vb->inflate_vq);
+	{
+		unsigned int used_len = tell_host(vb, vb->inflate_vq);
+
+		if (virtio_has_feature(vb->vdev,
+				       VIRTIO_BALLOON_F_DEVICE_INIT_ON_INFLATE) &&
+		    used_len >= DIV_ROUND_UP(VIRTIO_BALLOON_PAGES_PER_PAGE, 8)) {
+			unsigned int j;
+			bool zeroed = true;
+
+			for (j = 0; j < VIRTIO_BALLOON_PAGES_PER_PAGE; j++) {
+				if (!test_bit(j, vb->inflate_bitmap)) {
+					zeroed = false;
+					break;
+				}
+			}
+			if (zeroed)
+				__SetPageZeroed(newpage);
+		}
+	}
 
 	/* balloon's page migration 2nd step -- deflate "page" */
 	vb->num_pfns = VIRTIO_BALLOON_PAGES_PER_PAGE;
@@ -963,6 +1028,12 @@ static int virtballoon_probe(struct virtio_device *vdev)
 	if (err)
 		goto out_free_vb;
 
+	if (virtio_has_feature(vdev, VIRTIO_BALLOON_F_DEVICE_INIT_ON_INFLATE) &&
+	    virtqueue_get_vring_size(vb->inflate_vq) < 2) {
+		err = -ENOSPC;
+		goto out_del_vqs;
+	}
+
 	if (!virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_DEFLATE_ON_OOM))
 		vb->vb_dev_info.adjust_managed_page_count = true;
 #ifdef CONFIG_BALLOON_MIGRATION
@@ -1188,11 +1259,15 @@ static int virtballoon_validate(struct virtio_device *vdev)
 
 	/* Device fills with poison_val, not zeros; disable zeroed hint */
 	if (virtio_has_feature(vdev, VIRTIO_BALLOON_F_PAGE_POISON) &&
-	    !want_init_on_free())
+	    !want_init_on_free()) {
 		__virtio_clear_bit(vdev, VIRTIO_BALLOON_F_DEVICE_INIT_REPORTED);
+		__virtio_clear_bit(vdev, VIRTIO_BALLOON_F_DEVICE_INIT_ON_INFLATE);
+	}
 
-	if (cc_platform_has(CC_ATTR_GUEST_MEM_ENCRYPT))
+	if (cc_platform_has(CC_ATTR_GUEST_MEM_ENCRYPT)) {
 		__virtio_clear_bit(vdev, VIRTIO_BALLOON_F_DEVICE_INIT_REPORTED);
+		__virtio_clear_bit(vdev, VIRTIO_BALLOON_F_DEVICE_INIT_ON_INFLATE);
+	}
 	__virtio_clear_bit(vdev, VIRTIO_F_ACCESS_PLATFORM);
 	return 0;
 }
@@ -1205,6 +1280,7 @@ static unsigned int features[] = {
 	VIRTIO_BALLOON_F_PAGE_POISON,
 	VIRTIO_BALLOON_F_REPORTING,
 	VIRTIO_BALLOON_F_DEVICE_INIT_REPORTED,
+	VIRTIO_BALLOON_F_DEVICE_INIT_ON_INFLATE,
 };
 
 static struct virtio_driver virtio_balloon_driver = {
diff --git a/include/uapi/linux/virtio_balloon.h b/include/uapi/linux/virtio_balloon.h
index 13074631f300..cbaf18e0b17c 100644
--- a/include/uapi/linux/virtio_balloon.h
+++ b/include/uapi/linux/virtio_balloon.h
@@ -38,6 +38,7 @@
 #define VIRTIO_BALLOON_F_PAGE_POISON	4 /* Guest is using page poisoning */
 #define VIRTIO_BALLOON_F_REPORTING	5 /* Page reporting virtqueue */
 #define VIRTIO_BALLOON_F_DEVICE_INIT_REPORTED	6 /* Device initializes reported pages */
+#define VIRTIO_BALLOON_F_DEVICE_INIT_ON_INFLATE	7 /* Device initializes pages on inflate */
 
 /* Size of a PFN in the balloon interface. */
 #define VIRTIO_BALLOON_PFN_SHIFT 12
-- 
MST

[PATCH resend v6 30/30] mm: balloon: use put_page_zeroed for zeroed balloon pages

[Michael S. Tsirkin]

When a balloon page marked PageZeroed is freed during migration,
use put_page_zeroed() to propagate the zeroed hint to the buddy
allocator. Previously the hint was silently lost via plain put_page().

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Assisted-by: Claude:claude-opus-4-6
---
 mm/balloon.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/mm/balloon.c b/mm/balloon.c
index 96a8f1e20bc6..1bf7eb2642a9 100644
--- a/mm/balloon.c
+++ b/mm/balloon.c
@@ -324,7 +324,12 @@ static int balloon_page_migrate(struct page *newpage, struct page *page,
 	balloon_page_finalize(page);
 	spin_unlock_irqrestore(&balloon_pages_lock, flags);
 
-	put_page(page);
+	if (PageZeroed(page)) {
+		__ClearPageZeroed(page);
+		put_page_zeroed(page);
+	} else {
+		put_page(page);
+	}
 
 	return 0;
 }
-- 
MST