* [PATCH v10 36/37] mm: balloon: use put_page_zeroed for zeroed balloon pages
From: Michael S. Tsirkin @ 2026-06-08 8:40 UTC (permalink / raw)
To: linux-kernel
Cc: David Hildenbrand (Arm), Jason Wang, Xuan Zhuo,
Eugenio Pérez, Muchun Song, Oscar Salvador, Andrew Morton,
Lorenzo Stoakes, Liam R. Howlett, Vlastimil Babka, Mike Rapoport,
Suren Baghdasaryan, Michal Hocko, Brendan Jackman,
Johannes Weiner, Zi Yan, Baolin Wang, Nico Pache, Ryan Roberts,
Dev Jain, Barry Song, Lance Yang, Hugh Dickins, Matthew Brost,
Joshua Hahn, Rakie Kim, Byungchul Park, Gregory Price, Ying Huang,
Alistair Popple, Christoph Lameter, David Rientjes,
Roman Gushchin, Harry Yoo, Axel Rasmussen, Yuanchu Xie, Wei Xu,
Chris Li, Kairui Song, Kemeng Shi, Nhat Pham, Baoquan He,
virtualization, linux-mm, Andrea Arcangeli
In-Reply-To: <cover.1780906288.git.mst@redhat.com>
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().
No page has PageZeroed set yet; the next patch
(VIRTIO_BALLOON_F_DEVICE_INIT_ON_INFLATE) will set it on
pages the host has zeroed during inflate.
Note: during balloon migration, the migration core holds an
extra reference, so put_page_zeroed() will not be the final
put. The zeroed hint is lost in that case, which is
acceptable: it is a best-effort optimization.
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Assisted-by: Claude:claude-opus-4-6
---
mm/balloon.c | 10 +++++++++-
1 file changed, 9 insertions(+), 1 deletion(-)
diff --git a/mm/balloon.c b/mm/balloon.c
index 96a8f1e20bc6..6c9dd8ab0c5d 100644
--- a/mm/balloon.c
+++ b/mm/balloon.c
@@ -324,7 +324,15 @@ 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)) {
+ /* Atomic to serialize with memory_failure's
+ * TestSetPageHWPoison; not under zone->lock here.
+ */
+ ClearPageZeroed(page);
+ put_page_zeroed(page);
+ } else {
+ put_page(page);
+ }
return 0;
}
--
MST
^ permalink raw reply related
* [PATCH v10 35/37] virtio_balloon: disable reporting zeroed optimization for confidential guests
From: Michael S. Tsirkin @ 2026-06-08 8:40 UTC (permalink / raw)
To: linux-kernel
Cc: David Hildenbrand (Arm), Jason Wang, Xuan Zhuo,
Eugenio Pérez, Muchun Song, Oscar Salvador, Andrew Morton,
Lorenzo Stoakes, Liam R. Howlett, Vlastimil Babka, Mike Rapoport,
Suren Baghdasaryan, Michal Hocko, Brendan Jackman,
Johannes Weiner, Zi Yan, Baolin Wang, Nico Pache, Ryan Roberts,
Dev Jain, Barry Song, Lance Yang, Hugh Dickins, Matthew Brost,
Joshua Hahn, Rakie Kim, Byungchul Park, Gregory Price, Ying Huang,
Alistair Popple, Christoph Lameter, David Rientjes,
Roman Gushchin, Harry Yoo, Axel Rasmussen, Yuanchu Xie, Wei Xu,
Chris Li, Kairui Song, Kemeng Shi, Nhat Pham, Baoquan He,
virtualization, linux-mm, Andrea Arcangeli
In-Reply-To: <cover.1780906288.git.mst@redhat.com>
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.
Note: currently REPORTING remains enabled and
VIRTIO_F_ACCESS_PLATFORM is cleared in CC environments.
This is known to leak free page physical addresses to the
host. Whether that, or ballooning in general, is a security
concern in CC is up to the user. This patch only disables
our new zeroed-page hints where the host is untrusted.
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 e3afa6f32ba5..bf1172ad5419 100644
--- a/drivers/virtio/virtio_balloon.c
+++ b/drivers/virtio/virtio_balloon.c
@@ -19,6 +19,7 @@
#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
@@ -1193,6 +1194,8 @@ 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);
/*
* Balloon submits 1-2 sg entries max per buffer, virtqueue
* sizes are 128+. Disable indirect descriptors to avoid
--
MST
^ permalink raw reply related
* [PATCH v10 34/37] virtio_balloon: skip zeroing for host-zeroed reported pages
From: Michael S. Tsirkin @ 2026-06-08 8:40 UTC (permalink / raw)
To: linux-kernel
Cc: David Hildenbrand (Arm), Jason Wang, Xuan Zhuo,
Eugenio Pérez, Muchun Song, Oscar Salvador, Andrew Morton,
Lorenzo Stoakes, Liam R. Howlett, Vlastimil Babka, Mike Rapoport,
Suren Baghdasaryan, Michal Hocko, Brendan Jackman,
Johannes Weiner, Zi Yan, Baolin Wang, Nico Pache, Ryan Roberts,
Dev Jain, Barry Song, Lance Yang, Hugh Dickins, Matthew Brost,
Joshua Hahn, Rakie Kim, Byungchul Park, Gregory Price, Ying Huang,
Alistair Popple, Christoph Lameter, David Rientjes,
Roman Gushchin, Harry Yoo, Axel Rasmussen, Yuanchu Xie, Wei Xu,
Chris Li, Kairui Song, Kemeng Shi, Nhat Pham, Baoquan He,
virtualization, linux-mm, Andrea Arcangeli
In-Reply-To: <cover.1780906288.git.mst@redhat.com>
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 1fa1c7fa285f..e3afa6f32ba5 100644
--- a/drivers/virtio/virtio_balloon.c
+++ b/drivers/virtio/virtio_balloon.c
@@ -207,6 +207,8 @@ static int virtballoon_free_page_report(struct page_reporting_dev_info *pr_dev_i
struct virtqueue *vq = vb->reporting_vq;
unsigned int i, err = 0;
+ 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;
@@ -226,10 +228,14 @@ 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);
}
}
@@ -1051,6 +1057,9 @@ 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;
@@ -1176,6 +1185,14 @@ 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);
+
/*
* Balloon submits 1-2 sg entries max per buffer, virtqueue
* sizes are 128+. Disable indirect descriptors to avoid
@@ -1194,6 +1211,7 @@ 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
^ permalink raw reply related
* [PATCH v10 33/37] mm: page_reporting: add flush parameter with page budget
From: Michael S. Tsirkin @ 2026-06-08 8:40 UTC (permalink / raw)
To: linux-kernel
Cc: David Hildenbrand (Arm), Jason Wang, Xuan Zhuo,
Eugenio Pérez, Muchun Song, Oscar Salvador, Andrew Morton,
Lorenzo Stoakes, Liam R. Howlett, Vlastimil Babka, Mike Rapoport,
Suren Baghdasaryan, Michal Hocko, Brendan Jackman,
Johannes Weiner, Zi Yan, Baolin Wang, Nico Pache, Ryan Roberts,
Dev Jain, Barry Song, Lance Yang, Hugh Dickins, Matthew Brost,
Joshua Hahn, Rakie Kim, Byungchul Park, Gregory Price, Ying Huang,
Alistair Popple, Christoph Lameter, David Rientjes,
Roman Gushchin, Harry Yoo, Axel Rasmussen, Yuanchu Xie, Wei Xu,
Chris Li, Kairui Song, Kemeng Shi, Nhat Pham, Baoquan He,
virtualization, linux-mm, Andrea Arcangeli
In-Reply-To: <cover.1780906288.git.mst@redhat.com>
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
Note: the set callback runs under kernel param_lock,
so writing this parameter blocks other built-in parameter
writes until the flush loop completes. This is acceptable
for a privileged debug/test parameter.
Note: flush_delayed_work is called twice (once before the
main loop, once after). The first call ensures any pending
work completes before we submit new budget. The race with
__page_reporting_request is benign: if a concurrent request
arrives between our flushes, it queues new delayed work that
will run on its own schedule.
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 | 54 +++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 54 insertions(+)
diff --git a/mm/page_reporting.c b/mm/page_reporting.c
index 9c39448e758b..400150a2aa15 100644
--- a/mm/page_reporting.c
+++ b/mm/page_reporting.c
@@ -358,6 +358,60 @@ 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;
+ bool interrupted = false;
+
+ for (reported = 0; reported < budget;
+ reported += min(prdev->capacity, budget - reported)) {
+ /*
+ * First flush completes any previously scheduled
+ * reporting work. Then request a new reporting
+ * cycle and flush again to execute it.
+ */
+ 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)) {
+ interrupted = true;
+ break;
+ }
+ }
+ if (interrupted) {
+ mutex_unlock(&page_reporting_mutex);
+ return -EINTR;
+ }
+ }
+ 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
^ permalink raw reply related
* [PATCH v10 32/37] virtio_balloon: disable indirect descriptors
From: Michael S. Tsirkin @ 2026-06-08 8:40 UTC (permalink / raw)
To: linux-kernel
Cc: David Hildenbrand (Arm), Jason Wang, Xuan Zhuo,
Eugenio Pérez, Muchun Song, Oscar Salvador, Andrew Morton,
Lorenzo Stoakes, Liam R. Howlett, Vlastimil Babka, Mike Rapoport,
Suren Baghdasaryan, Michal Hocko, Brendan Jackman,
Johannes Weiner, Zi Yan, Baolin Wang, Nico Pache, Ryan Roberts,
Dev Jain, Barry Song, Lance Yang, Hugh Dickins, Matthew Brost,
Joshua Hahn, Rakie Kim, Byungchul Park, Gregory Price, Ying Huang,
Alistair Popple, Christoph Lameter, David Rientjes,
Roman Gushchin, Harry Yoo, Axel Rasmussen, Yuanchu Xie, Wei Xu,
Chris Li, Kairui Song, Kemeng Shi, Nhat Pham, Baoquan He,
virtualization, linux-mm, Andrea Arcangeli
In-Reply-To: <cover.1780906288.git.mst@redhat.com>
A follow-up patch (DEVICE_INIT_ON_INFLATE) adds an inbuf
(bitmap) alongside the outbuf (pfns), making total_sg=2.
With INDIRECT_DESC negotiated, virtqueue_use_indirect()
triggers for total_sg > 1. Balloon never needs more than
2 entries and virtqueue sizes are 128+, so indirect
descriptors are unnecessary.
Disabling them avoids a GFP_KERNEL allocation inside
virtqueue_add_sgs when VIRTIO_RING_F_INDIRECT_DESC is negotiated.
This allocation could trigger OOM reclaim while balloon_lock is
held, leading to a deadlock: OOM notifier -> leak_balloon ->
balloon_lock.
With single-buffer submissions (previous patch) and no indirect
descriptors, virtqueue_add never allocates memory.
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Assisted-by: Claude:claude-opus-4-6
---
drivers/virtio/virtio_balloon.c | 8 ++++++++
1 file changed, 8 insertions(+)
diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
index 53b4a3984e7d..1fa1c7fa285f 100644
--- a/drivers/virtio/virtio_balloon.c
+++ b/drivers/virtio/virtio_balloon.c
@@ -7,6 +7,7 @@
*/
#include <linux/virtio.h>
+#include <uapi/linux/virtio_ring.h>
#include <linux/virtio_balloon.h>
#include <linux/swap.h>
#include <linux/workqueue.h>
@@ -1175,6 +1176,13 @@ 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);
+ /*
+ * Balloon submits 1-2 sg entries max per buffer, virtqueue
+ * sizes are 128+. Disable indirect descriptors to avoid
+ * GFP_KERNEL allocation in virtqueue_add under balloon_lock,
+ * which could deadlock via OOM -> oom_notify -> leak_balloon.
+ */
+ __virtio_clear_bit(vdev, VIRTIO_RING_F_INDIRECT_DESC);
__virtio_clear_bit(vdev, VIRTIO_F_ACCESS_PLATFORM);
return 0;
}
--
MST
^ permalink raw reply related
* [PATCH v10 31/37] virtio_balloon: submit reported pages as individual buffers
From: Michael S. Tsirkin @ 2026-06-08 8:39 UTC (permalink / raw)
To: linux-kernel
Cc: David Hildenbrand (Arm), Jason Wang, Xuan Zhuo,
Eugenio Pérez, Muchun Song, Oscar Salvador, Andrew Morton,
Lorenzo Stoakes, Liam R. Howlett, Vlastimil Babka, Mike Rapoport,
Suren Baghdasaryan, Michal Hocko, Brendan Jackman,
Johannes Weiner, Zi Yan, Baolin Wang, Nico Pache, Ryan Roberts,
Dev Jain, Barry Song, Lance Yang, Hugh Dickins, Matthew Brost,
Joshua Hahn, Rakie Kim, Byungchul Park, Gregory Price, Ying Huang,
Alistair Popple, Christoph Lameter, David Rientjes,
Roman Gushchin, Harry Yoo, Axel Rasmussen, Yuanchu Xie, Wei Xu,
Chris Li, Kairui Song, Kemeng Shi, Nhat Pham, Baoquan He,
virtualization, linux-mm, Andrea Arcangeli
In-Reply-To: <cover.1780906288.git.mst@redhat.com>
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.
Note: if the virtqueue is broken, wait_event on
virtqueue_get_buf hangs. This is a pre-existing issue:
the old single-buffer code had the same hang. EVENT_IDX
is not a concern: callbacks were never disabled, so the
virtqueue manages used_event automatically.
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Assisted-by: Claude:claude-opus-4-6
---
drivers/virtio/virtio_balloon.c | 40 +++++++++++++++++++++------------
1 file changed, 26 insertions(+), 14 deletions(-)
diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
index 6a1a610c2cb1..53b4a3984e7d 100644
--- a/drivers/virtio/virtio_balloon.c
+++ b/drivers/virtio/virtio_balloon.c
@@ -187,7 +187,9 @@ static void tell_host(struct virtio_balloon *vb, struct virtqueue *vq)
sg_init_one(&sg, vb->pfns, sizeof(vb->pfns[0]) * vb->num_pfns);
- /* We should always be able to add one buffer to an empty queue. */
+ /* We made sure the vq is large enough so we should always
+ * be able to add one buffer to an empty queue.
+ */
virtqueue_add_outbuf(vq, &sg, 1, vb, GFP_KERNEL);
virtqueue_kick(vq);
@@ -202,25 +204,35 @@ 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 = 0;
/* 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
^ permalink raw reply related
* [PATCH v10 30/37] mm: page_reporting: add per-page zeroed bitmap for host feedback
From: Michael S. Tsirkin @ 2026-06-08 8:39 UTC (permalink / raw)
To: linux-kernel
Cc: David Hildenbrand (Arm), Jason Wang, Xuan Zhuo,
Eugenio Pérez, Muchun Song, Oscar Salvador, Andrew Morton,
Lorenzo Stoakes, Liam R. Howlett, Vlastimil Babka, Mike Rapoport,
Suren Baghdasaryan, Michal Hocko, Brendan Jackman,
Johannes Weiner, Zi Yan, Baolin Wang, Nico Pache, Ryan Roberts,
Dev Jain, Barry Song, Lance Yang, Hugh Dickins, Matthew Brost,
Joshua Hahn, Rakie Kim, Byungchul Park, Gregory Price, Ying Huang,
Alistair Popple, Christoph Lameter, David Rientjes,
Roman Gushchin, Harry Yoo, Axel Rasmussen, Yuanchu Xie, Wei Xu,
Chris Li, Kairui Song, Kemeng Shi, Nhat Pham, Baoquan He,
virtualization, linux-mm, Andrea Arcangeli
In-Reply-To: <cover.1780906288.git.mst@redhat.com>
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 84ebc4547119..9c39448e758b 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
^ permalink raw reply related
* [PATCH v10 29/37] mm: memfd: skip zeroing for zeroed hugetlb pool pages
From: Michael S. Tsirkin @ 2026-06-08 8:39 UTC (permalink / raw)
To: linux-kernel
Cc: David Hildenbrand (Arm), Jason Wang, Xuan Zhuo,
Eugenio Pérez, Muchun Song, Oscar Salvador, Andrew Morton,
Lorenzo Stoakes, Liam R. Howlett, Vlastimil Babka, Mike Rapoport,
Suren Baghdasaryan, Michal Hocko, Brendan Jackman,
Johannes Weiner, Zi Yan, Baolin Wang, Nico Pache, Ryan Roberts,
Dev Jain, Barry Song, Lance Yang, Hugh Dickins, Matthew Brost,
Joshua Hahn, Rakie Kim, Byungchul Park, Gregory Price, Ying Huang,
Alistair Popple, Christoph Lameter, David Rientjes,
Roman Gushchin, Harry Yoo, Axel Rasmussen, Yuanchu Xie, Wei Xu,
Chris Li, Kairui Song, Kemeng Shi, Nhat Pham, Baoquan He,
virtualization, linux-mm, Andrea Arcangeli
In-Reply-To: <cover.1780906288.git.mst@redhat.com>
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.
Note: HPG_zeroed is currently only set for surplus pages
allocated with __GFP_ZERO (via alloc_surplus_hugetlb_folio),
not for pool pages from alloc_pool_huge_folio. So the
zeroed output from alloc_hugetlb_folio_reserve is typically
false for pool-only reservations. It becomes true when
surplus pages fill the reservation. The addr_hint 0 passed
to folio_zero_user is acceptable for memfd: these pages are
not mapped yet and will get proper dcache handling at mmap
time via the page fault path.
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Assisted-by: Claude:claude-opus-4-6
---
include/linux/cma.h | 3 ++-
include/linux/hugetlb.h | 6 ++++--
mm/cma.c | 6 ++++--
mm/hugetlb.c | 11 +++++++++--
mm/hugetlb_cma.c | 4 ++--
mm/memfd.c | 14 ++++++++------
6 files changed, 29 insertions(+), 15 deletions(-)
diff --git a/include/linux/cma.h b/include/linux/cma.h
index 8555d38a97b1..dee88909cf5d 100644
--- a/include/linux/cma.h
+++ b/include/linux/cma.h
@@ -53,7 +53,8 @@ extern bool cma_release(struct cma *cma, const struct page *pages, unsigned long
struct page *cma_alloc_frozen(struct cma *cma, unsigned long count,
unsigned int align, bool no_warn);
-struct page *cma_alloc_frozen_compound(struct cma *cma, unsigned int order);
+struct page *cma_alloc_frozen_compound(struct cma *cma, unsigned int order,
+ gfp_t caller_gfp);
bool cma_release_frozen(struct cma *cma, const struct page *pages,
unsigned long count);
diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
index 06d033a57a61..7eb529eabe99 100644
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -708,7 +708,8 @@ 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);
@@ -1128,7 +1129,8 @@ static inline void wait_for_freed_hugetlb_folios(void)
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/cma.c b/mm/cma.c
index c7ca567f4c5c..27971f6264ab 100644
--- a/mm/cma.c
+++ b/mm/cma.c
@@ -924,9 +924,11 @@ struct page *cma_alloc_frozen(struct cma *cma, unsigned long count,
return __cma_alloc_frozen(cma, count, align, gfp);
}
-struct page *cma_alloc_frozen_compound(struct cma *cma, unsigned int order)
+struct page *cma_alloc_frozen_compound(struct cma *cma, unsigned int order,
+ gfp_t caller_gfp)
{
- gfp_t gfp = GFP_KERNEL | __GFP_COMP | __GFP_NOWARN;
+ gfp_t gfp = GFP_KERNEL | __GFP_COMP | __GFP_NOWARN |
+ (caller_gfp & __GFP_ZERO);
return __cma_alloc_frozen(cma, 1 << order, order, gfp);
}
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index ed00db703911..a087e915783f 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -2196,7 +2196,7 @@ 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;
@@ -2212,6 +2212,12 @@ 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;
}
@@ -2296,7 +2302,8 @@ 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),
NUMA_NO_NODE, &alloc_nodemask,
USER_ADDR_NONE);
if (!folio) {
diff --git a/mm/hugetlb_cma.c b/mm/hugetlb_cma.c
index 7693ccefd0c6..c9266b25be3d 100644
--- a/mm/hugetlb_cma.c
+++ b/mm/hugetlb_cma.c
@@ -35,14 +35,14 @@ struct folio *hugetlb_cma_alloc_frozen_folio(int order, gfp_t gfp_mask,
return NULL;
if (hugetlb_cma[nid])
- page = cma_alloc_frozen_compound(hugetlb_cma[nid], order);
+ page = cma_alloc_frozen_compound(hugetlb_cma[nid], order, gfp_mask);
if (!page && !(gfp_mask & __GFP_THISNODE)) {
for_each_node_mask(node, *nodemask) {
if (node == nid || !hugetlb_cma[node])
continue;
- page = cma_alloc_frozen_compound(hugetlb_cma[node], order);
+ page = cma_alloc_frozen_compound(hugetlb_cma[node], order, gfp_mask);
if (page)
break;
}
diff --git a/mm/memfd.c b/mm/memfd.c
index abe13b291ddc..a99617a62e33 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
^ permalink raw reply related
* [PATCH v10 28/37] mm: hugetlb: add gfp parameter and skip zeroing for zeroed pages
From: Michael S. Tsirkin @ 2026-06-08 8:39 UTC (permalink / raw)
To: linux-kernel
Cc: David Hildenbrand (Arm), Jason Wang, Xuan Zhuo,
Eugenio Pérez, Muchun Song, Oscar Salvador, Andrew Morton,
Lorenzo Stoakes, Liam R. Howlett, Vlastimil Babka, Mike Rapoport,
Suren Baghdasaryan, Michal Hocko, Brendan Jackman,
Johannes Weiner, Zi Yan, Baolin Wang, Nico Pache, Ryan Roberts,
Dev Jain, Barry Song, Lance Yang, Hugh Dickins, Matthew Brost,
Joshua Hahn, Rakie Kim, Byungchul Park, Gregory Price, Ying Huang,
Alistair Popple, Christoph Lameter, David Rientjes,
Roman Gushchin, Harry Yoo, Axel Rasmussen, Yuanchu Xie, Wei Xu,
Chris Li, Kairui Song, Kemeng Shi, Nhat Pham, Baoquan He,
virtualization, linux-mm, Andrea Arcangeli
In-Reply-To: <cover.1780906288.git.mst@redhat.com>
Add a gfp_t parameter to alloc_hugetlb_folio(). When __GFP_ZERO
is set, the function guarantees the returned folio is zeroed:
- Fresh allocations (buddy or gigantic): zeroed by
post_alloc_hook via __GFP_ZERO, HPG_zeroed set by
alloc_surplus_hugetlb_folio.
- Pool pages with HPG_zeroed set: already zeroed, skip.
- Pool pages without HPG_zeroed: zeroed via folio_zero_user().
The address parameter is renamed to user_addr; the function
aligns it internally for reservation and NUMA policy lookups.
For pages that need zeroing, user_addr is passed to
folio_zero_user() for cache-friendly zeroing near the faulting
subpage. All callers pass a page-aligned address; the
hugetlb_no_page caller passes vmf->real_address & PAGE_MASK
for consistency.
HPG_zeroed (stored in hugetlb folio->private bits) tracks
known-zero pool pages. It is set when alloc_surplus_hugetlb_folio
allocates with __GFP_ZERO, and cleared in free_huge_folio when
the page returns to the pool after userspace use.
Note: for gigantic CMA pages, __GFP_ZERO is passed through
to cma_alloc_frozen_compound() via its caller_gfp parameter,
so the pages ARE zeroed by the allocator. HPG_zeroed is only
set when __GFP_ZERO was in the original gfp_mask.
Pool pages allocated without __GFP_ZERO (e.g. by
alloc_pool_huge_folio) do not get HPG_zeroed; they are zeroed
later by folio_zero_user() at fault time.
Note: with __GFP_ZERO, the folio is zeroed before
mem_cgroup_charge_hugetlb(). If the charge fails, the zeroed
folio is freed back. Before this patch it is zeroed after charge, so
simply freeing after zeroing would be a regression. Thread a
zeroed hint through free_huge_folio so surplus pages freed back
to buddy preserve the zeroed state via free_frozen_pages_zeroed,
avoiding redundant re-zeroing on the next allocation.
Suggested-by: Gregory Price <gourry@gourry.net>
Reviewed-by: Gregory Price <gourry@gourry.net>
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 | 3 +-
include/linux/hugetlb.h | 5 ++-
mm/hugetlb.c | 78 +++++++++++++++++++++++++++--------------
3 files changed, 57 insertions(+), 29 deletions(-)
diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
index 78d61bf2bd9b..2c0c51fe9ec3 100644
--- a/fs/hugetlbfs/inode.c
+++ b/fs/hugetlbfs/inode.c
@@ -790,13 +790,12 @@ 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);
+ folio = alloc_hugetlb_folio(&pseudo_vma, addr, false, __GFP_ZERO);
if (IS_ERR(folio)) {
mutex_unlock(&hugetlb_fault_mutex_table[hash]);
error = PTR_ERR(folio);
goto out;
}
- folio_zero_user(folio, addr);
__folio_mark_uptodate(folio);
error = hugetlb_add_to_page_cache(folio, mapping, index);
if (unlikely(error)) {
diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
index 1f7ae6609e51..06d033a57a61 100644
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -593,6 +593,7 @@ enum hugetlb_page_flags {
HPG_vmemmap_optimized,
HPG_raw_hwp_unreliable,
HPG_cma,
+ HPG_zeroed,
__NR_HPAGEFLAGS,
};
@@ -653,6 +654,7 @@ HPAGEFLAG(Freed, freed)
HPAGEFLAG(VmemmapOptimized, vmemmap_optimized)
HPAGEFLAG(RawHwpUnreliable, raw_hwp_unreliable)
HPAGEFLAG(Cma, cma)
+HPAGEFLAG(Zeroed, zeroed)
#ifdef CONFIG_HUGETLB_PAGE
@@ -700,7 +702,8 @@ 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 user_addr, bool cow_from_owner,
+ gfp_t gfp);
struct folio *alloc_hugetlb_folio_nodemask(struct hstate *h, int preferred_nid,
nodemask_t *nmask, gfp_t gfp_mask,
bool allow_alloc_fallback);
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 5d7e546565f5..ed00db703911 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -1455,7 +1455,8 @@ void add_hugetlb_folio(struct hstate *h, struct folio *folio,
}
static void __update_and_free_hugetlb_folio(struct hstate *h,
- struct folio *folio)
+ struct folio *folio,
+ bool zeroed)
{
bool clear_flag = folio_test_hugetlb_vmemmap_optimized(folio);
@@ -1506,6 +1507,8 @@ static void __update_and_free_hugetlb_folio(struct hstate *h,
VM_BUG_ON_FOLIO(folio_ref_count(folio), folio);
if (folio_test_hugetlb_cma(folio))
hugetlb_cma_free_frozen_folio(folio);
+ else if (zeroed)
+ free_frozen_pages_zeroed(&folio->page, folio_order(folio));
else
free_frozen_pages(&folio->page, folio_order(folio));
}
@@ -1545,7 +1548,7 @@ static void free_hpage_workfn(struct work_struct *work)
*/
h = size_to_hstate(folio_size(folio));
- __update_and_free_hugetlb_folio(h, folio);
+ __update_and_free_hugetlb_folio(h, folio, false);
cond_resched();
}
@@ -1559,10 +1562,10 @@ static inline void flush_free_hpage_work(struct hstate *h)
}
static void update_and_free_hugetlb_folio(struct hstate *h, struct folio *folio,
- bool atomic)
+ bool atomic, bool zeroed)
{
if (!folio_test_hugetlb_vmemmap_optimized(folio) || !atomic) {
- __update_and_free_hugetlb_folio(h, folio);
+ __update_and_free_hugetlb_folio(h, folio, zeroed);
return;
}
@@ -1596,7 +1599,7 @@ static void bulk_vmemmap_restore_error(struct hstate *h,
spin_lock_irq(&hugetlb_lock);
__folio_clear_hugetlb(folio);
spin_unlock_irq(&hugetlb_lock);
- update_and_free_hugetlb_folio(h, folio, false);
+ update_and_free_hugetlb_folio(h, folio, false, false);
cond_resched();
}
} else {
@@ -1621,7 +1624,7 @@ static void bulk_vmemmap_restore_error(struct hstate *h,
spin_lock_irq(&hugetlb_lock);
__folio_clear_hugetlb(folio);
spin_unlock_irq(&hugetlb_lock);
- update_and_free_hugetlb_folio(h, folio, false);
+ update_and_free_hugetlb_folio(h, folio, false, false);
cond_resched();
break;
}
@@ -1664,7 +1667,7 @@ static void update_and_free_pages_bulk(struct hstate *h,
}
list_for_each_entry_safe(folio, t_folio, &non_hvo_folios, lru) {
- update_and_free_hugetlb_folio(h, folio, false);
+ update_and_free_hugetlb_folio(h, folio, false, false);
cond_resched();
}
}
@@ -1680,7 +1683,7 @@ struct hstate *size_to_hstate(unsigned long size)
return NULL;
}
-void free_huge_folio(struct folio *folio)
+static void __free_huge_folio(struct folio *folio, bool zeroed)
{
/*
* Can't pass hstate in here because it is called from the
@@ -1692,6 +1695,9 @@ void free_huge_folio(struct folio *folio)
bool restore_reserve;
unsigned long flags;
+ /* Page was mapped to userspace; no longer known-zero */
+ folio_clear_hugetlb_zeroed(folio);
+
VM_BUG_ON_FOLIO(folio_ref_count(folio), folio);
VM_BUG_ON_FOLIO(folio_mapcount(folio), folio);
@@ -1735,12 +1741,12 @@ void free_huge_folio(struct folio *folio)
if (folio_test_hugetlb_temporary(folio)) {
remove_hugetlb_folio(h, folio, false);
spin_unlock_irqrestore(&hugetlb_lock, flags);
- update_and_free_hugetlb_folio(h, folio, true);
+ update_and_free_hugetlb_folio(h, folio, true, zeroed);
} else if (h->surplus_huge_pages_node[nid]) {
/* remove the page from active list */
remove_hugetlb_folio(h, folio, true);
spin_unlock_irqrestore(&hugetlb_lock, flags);
- update_and_free_hugetlb_folio(h, folio, true);
+ update_and_free_hugetlb_folio(h, folio, true, zeroed);
} else {
arch_clear_hugetlb_flags(folio);
enqueue_hugetlb_folio(h, folio);
@@ -1748,6 +1754,11 @@ void free_huge_folio(struct folio *folio)
}
}
+void free_huge_folio(struct folio *folio)
+{
+ __free_huge_folio(folio, false);
+}
+
/*
* Must be called with the hugetlb lock held
*/
@@ -2031,7 +2042,7 @@ int dissolve_free_hugetlb_folio(struct folio *folio)
rc = 0;
}
- update_and_free_hugetlb_folio(h, folio, false);
+ update_and_free_hugetlb_folio(h, folio, false, false);
return rc;
}
out:
@@ -2093,6 +2104,10 @@ 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
@@ -2156,11 +2171,11 @@ 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;
@@ -2715,7 +2730,7 @@ static int alloc_and_dissolve_hugetlb_folio(struct folio *old_folio,
* Folio has been replaced, we can safely free the old one.
*/
spin_unlock_irq(&hugetlb_lock);
- update_and_free_hugetlb_folio(h, old_folio, false);
+ update_and_free_hugetlb_folio(h, old_folio, false, false);
}
return ret;
@@ -2723,7 +2738,7 @@ static int alloc_and_dissolve_hugetlb_folio(struct folio *old_folio,
free_new:
spin_unlock_irq(&hugetlb_lock);
if (new_folio)
- update_and_free_hugetlb_folio(h, new_folio, false);
+ update_and_free_hugetlb_folio(h, new_folio, false, false);
return ret;
}
@@ -2857,16 +2872,19 @@ 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 user_addr, bool cow_from_owner,
+ gfp_t gfp)
{
struct hugepage_subpool *spool = subpool_vma(vma);
struct hstate *h = hstate_vma(vma);
+ unsigned long addr = user_addr & huge_page_mask(h);
struct folio *folio;
long retval, gbl_chg, gbl_reserve;
map_chg_state map_chg;
int ret, idx;
struct hugetlb_cgroup *h_cg = NULL;
- gfp_t gfp = htlb_alloc_mask(h) | __GFP_RETRY_MAYFAIL;
+
+ gfp |= htlb_alloc_mask(h) | __GFP_RETRY_MAYFAIL;
idx = hstate_index(h);
@@ -2934,13 +2952,12 @@ 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, user_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 */
}
/*
@@ -2963,6 +2980,10 @@ struct folio *alloc_hugetlb_folio(struct vm_area_struct *vma,
spin_unlock_irq(&hugetlb_lock);
+ if ((gfp & __GFP_ZERO) && !folio_test_hugetlb_zeroed(folio))
+ folio_zero_user(folio, user_addr);
+ folio_clear_hugetlb_zeroed(folio);
+
hugetlb_set_folio_subpool(folio, spool);
if (map_chg != MAP_CHG_ENFORCED) {
@@ -2999,7 +3020,7 @@ struct folio *alloc_hugetlb_folio(struct vm_area_struct *vma,
lruvec_stat_mod_folio(folio, NR_HUGETLB, pages_per_huge_page(h));
if (ret == -ENOMEM) {
- free_huge_folio(folio);
+ __free_huge_folio(folio, !!(gfp & __GFP_ZERO));
return ERR_PTR(-ENOMEM);
}
@@ -4971,7 +4992,7 @@ 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);
if (IS_ERR(new_folio)) {
folio_put(pte_folio);
ret = PTR_ERR(new_folio);
@@ -5500,7 +5521,7 @@ 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);
if (IS_ERR(new_folio)) {
/*
@@ -5760,7 +5781,13 @@ static vm_fault_t hugetlb_no_page(struct address_space *mapping,
goto out;
}
- folio = alloc_hugetlb_folio(vma, vmf->address, false);
+ /*
+ * Passing vmf->real_address would work just as well,
+ * but PAGE_MASK helps make sure we never pass
+ * USER_ADDR_NONE by mistake.
+ */
+ folio = alloc_hugetlb_folio(vma, vmf->real_address & PAGE_MASK,
+ false, __GFP_ZERO);
if (IS_ERR(folio)) {
/*
* Returning error will result in faulting task being
@@ -5780,7 +5807,6 @@ static vm_fault_t hugetlb_no_page(struct address_space *mapping,
ret = 0;
goto out;
}
- folio_zero_user(folio, vmf->real_address);
__folio_mark_uptodate(folio);
new_folio = true;
@@ -6219,7 +6245,7 @@ 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);
if (IS_ERR(folio)) {
pte_t *actual_pte = hugetlb_walk(dst_vma, dst_addr, PMD_SIZE);
if (actual_pte) {
@@ -6266,7 +6292,7 @@ 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);
if (IS_ERR(folio)) {
folio_put(*foliop);
ret = -ENOMEM;
--
MST
^ permalink raw reply related
* [PATCH v10 27/37] mm: use __GFP_ZERO in vma_alloc_anon_folio_pmd
From: Michael S. Tsirkin @ 2026-06-08 8:39 UTC (permalink / raw)
To: linux-kernel
Cc: David Hildenbrand (Arm), Jason Wang, Xuan Zhuo,
Eugenio Pérez, Muchun Song, Oscar Salvador, Andrew Morton,
Lorenzo Stoakes, Liam R. Howlett, Vlastimil Babka, Mike Rapoport,
Suren Baghdasaryan, Michal Hocko, Brendan Jackman,
Johannes Weiner, Zi Yan, Baolin Wang, Nico Pache, Ryan Roberts,
Dev Jain, Barry Song, Lance Yang, Hugh Dickins, Matthew Brost,
Joshua Hahn, Rakie Kim, Byungchul Park, Gregory Price, Ying Huang,
Alistair Popple, Christoph Lameter, David Rientjes,
Roman Gushchin, Harry Yoo, Axel Rasmussen, Yuanchu Xie, Wei Xu,
Chris Li, Kairui Song, Kemeng Shi, Nhat Pham, Baoquan He,
virtualization, linux-mm, Andrea Arcangeli
In-Reply-To: <cover.1780906288.git.mst@redhat.com>
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.
Note: before this series, replacing folio_zero_user() with
__GFP_ZERO was unsafe on cache-aliasing architectures because
__GFP_ZERO uses clear_page() without a dcache flush. With this
series, it is safe if the caller passes a valid user address
(not USER_ADDR_NONE) to vma_alloc_folio() etc., which delivers
it to post_alloc_hook() for the dcache flush via
folio_zero_user(). It is only unsafe if USER_ADDR_NONE is passed.
Note: with __GFP_ZERO, the folio is zeroed before
mem_cgroup_charge(). If the charge fails, the zeroing work is
wasted. Previously zeroing was done after a successful charge.
This is inherent to moving zeroing into the allocator.
Charge failures are rare (only at cgroup limits).
Use folio_put_zeroed() on charge failure so the zeroed hint
propagates to the buddy allocator, avoiding redundant re-zeroing
on the next allocation attempt.
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Gregory Price <gourry@gourry.net>
Assisted-by: Claude:claude-opus-4-6
---
mm/huge_memory.c | 14 +++-----------
1 file changed, 3 insertions(+), 11 deletions(-)
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index d689e6491ddb..0dec3c717ff2 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;
@@ -1347,7 +1347,7 @@ static struct folio *vma_alloc_anon_folio_pmd(struct vm_area_struct *vma,
VM_BUG_ON_FOLIO(!folio_test_large(folio), folio);
if (mem_cgroup_charge(folio, vma->vm_mm, gfp)) {
- folio_put(folio);
+ folio_put_zeroed(folio);
count_vm_event(THP_FAULT_FALLBACK);
count_vm_event(THP_FAULT_FALLBACK_CHARGE);
count_mthp_stat(order, MTHP_STAT_ANON_FAULT_FALLBACK);
@@ -1356,17 +1356,9 @@ 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()
+ * page zeroing becomes visible before the set_pmd_at()
* write.
*/
__folio_mark_uptodate(folio);
--
MST
^ permalink raw reply related
* [PATCH v10 26/37] mm: vma_alloc_anon_folio_pmd: pass raw fault address to vma_alloc_folio
From: Michael S. Tsirkin @ 2026-06-08 8:39 UTC (permalink / raw)
To: linux-kernel
Cc: David Hildenbrand (Arm), Jason Wang, Xuan Zhuo,
Eugenio Pérez, Muchun Song, Oscar Salvador, Andrew Morton,
Lorenzo Stoakes, Liam R. Howlett, Vlastimil Babka, Mike Rapoport,
Suren Baghdasaryan, Michal Hocko, Brendan Jackman,
Johannes Weiner, Zi Yan, Baolin Wang, Nico Pache, Ryan Roberts,
Dev Jain, Barry Song, Lance Yang, Hugh Dickins, Matthew Brost,
Joshua Hahn, Rakie Kim, Byungchul Park, Gregory Price, Ying Huang,
Alistair Popple, Christoph Lameter, David Rientjes,
Roman Gushchin, Harry Yoo, Axel Rasmussen, Yuanchu Xie, Wei Xu,
Chris Li, Kairui Song, Kemeng Shi, Nhat Pham, Baoquan He,
virtualization, linux-mm, Andrea Arcangeli
In-Reply-To: <cover.1780906288.git.mst@redhat.com>
Drop the redundant HPAGE_PMD_MASK alignment at the callsite.
NUMA interleave is not affected by the raw address; the ilx
calculation shifts addr >> PAGE_SHIFT >> order, dropping
sub-page bits regardless of alignment. post_alloc_hook will
use the raw address for cache-friendly zeroing.
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Assisted-by: Claude:claude-opus-4-6
Reviewed-by: Gregory Price <gourry@gourry.net>
---
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
^ permalink raw reply related
* [PATCH v10 25/37] mm: use __GFP_ZERO in alloc_anon_folio
From: Michael S. Tsirkin @ 2026-06-08 8:39 UTC (permalink / raw)
To: linux-kernel
Cc: David Hildenbrand (Arm), Jason Wang, Xuan Zhuo,
Eugenio Pérez, Muchun Song, Oscar Salvador, Andrew Morton,
Lorenzo Stoakes, Liam R. Howlett, Vlastimil Babka, Mike Rapoport,
Suren Baghdasaryan, Michal Hocko, Brendan Jackman,
Johannes Weiner, Zi Yan, Baolin Wang, Nico Pache, Ryan Roberts,
Dev Jain, Barry Song, Lance Yang, Hugh Dickins, Matthew Brost,
Joshua Hahn, Rakie Kim, Byungchul Park, Gregory Price, Ying Huang,
Alistair Popple, Christoph Lameter, David Rientjes,
Roman Gushchin, Harry Yoo, Axel Rasmussen, Yuanchu Xie, Wei Xu,
Chris Li, Kairui Song, Kemeng Shi, Nhat Pham, Baoquan He,
virtualization, linux-mm, Andrea Arcangeli
In-Reply-To: <cover.1780906288.git.mst@redhat.com>
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.
Note: before this series, replacing clear_user_highpage() with
__GFP_ZERO was unsafe on cache-aliasing architectures because
__GFP_ZERO uses clear_page() without a dcache flush. With this
series, it is safe if the caller passes a valid user address
(not USER_ADDR_NONE) to vma_alloc_folio() etc., which delivers
it to post_alloc_hook() for the dcache flush via
folio_zero_user(). It is only unsafe if USER_ADDR_NONE is passed.
Note: with __GFP_ZERO, the folio is zeroed before
mem_cgroup_charge(). If the charge fails, the zeroing work is
wasted. Previously zeroing was done after a successful charge.
This is inherent to moving zeroing into the allocator.
Charge failures are rare (only at cgroup limits).
Use folio_put_zeroed() on charge failure so the zeroed hint
propagates to the buddy allocator, avoiding redundant re-zeroing
on the next allocation attempt.
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Gregory Price <gourry@gourry.net>
Assisted-by: Claude:claude-opus-4-6
---
mm/memory.c | 13 ++-----------
1 file changed, 2 insertions(+), 11 deletions(-)
diff --git a/mm/memory.c b/mm/memory.c
index 6c14b90f558e..6d6a3e1a02c1 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -5265,25 +5265,16 @@ 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) {
if (mem_cgroup_charge(folio, vma->vm_mm, gfp)) {
count_mthp_stat(order, MTHP_STAT_ANON_FAULT_FALLBACK_CHARGE);
- folio_put(folio);
+ folio_put_zeroed(folio);
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
^ permalink raw reply related
* [PATCH v10 24/37] mm: add put_page_zeroed and folio_put_zeroed
From: Michael S. Tsirkin @ 2026-06-08 8:38 UTC (permalink / raw)
To: linux-kernel
Cc: David Hildenbrand (Arm), Jason Wang, Xuan Zhuo,
Eugenio Pérez, Muchun Song, Oscar Salvador, Andrew Morton,
Lorenzo Stoakes, Liam R. Howlett, Vlastimil Babka, Mike Rapoport,
Suren Baghdasaryan, Michal Hocko, Brendan Jackman,
Johannes Weiner, Zi Yan, Baolin Wang, Nico Pache, Ryan Roberts,
Dev Jain, Barry Song, Lance Yang, Hugh Dickins, Matthew Brost,
Joshua Hahn, Rakie Kim, Byungchul Park, Gregory Price, Ying Huang,
Alistair Popple, Christoph Lameter, David Rientjes,
Roman Gushchin, Harry Yoo, Axel Rasmussen, Yuanchu Xie, Wei Xu,
Chris Li, Kairui Song, Kemeng Shi, Nhat Pham, Baoquan He,
virtualization, linux-mm, Andrea Arcangeli
In-Reply-To: <cover.1780906288.git.mst@redhat.com>
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 zeroed hint is
propagated to the buddy allocator. 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.
Note: put_page_zeroed uses folio_put_testzero() which only
detects sole ownership at the instant of the atomic decrement.
A concurrent reference holder (e.g. migration) means the hint
is silently lost. This is by design: the zeroed hint is a
performance optimization, not a correctness requirement.
Losing it just means the next allocation re-zeroes the page.
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Assisted-by: Claude:claude-opus-4-6
---
include/linux/mm.h | 13 +++++++++++++
mm/swap.c | 20 ++++++++++++++++++--
2 files changed, 31 insertions(+), 2 deletions(-)
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 06bbe9eba636..79b3a8cb9a3b 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 +2091,18 @@ static inline void folio_put(struct folio *folio)
__folio_put(folio);
}
+/* Caller must be sole owner to guarantee page is still zero */
+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..ecec780172ad 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -94,13 +94,15 @@ 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)
{
+ /* zeroed hint ignored for now, no current user */
if (unlikely(folio_is_zone_device(folio))) {
free_zone_device_folio(folio);
return;
}
+ /* zeroed hint ignored for now, no current user */
if (folio_test_hugetlb(folio)) {
free_huge_folio(folio);
return;
@@ -109,10 +111,24 @@ 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
^ permalink raw reply related
* [PATCH v10 23/37] mm: page_alloc: skip kernel_init_pages for FPI_ZEROED when safe
From: Michael S. Tsirkin @ 2026-06-08 8:38 UTC (permalink / raw)
To: linux-kernel
Cc: David Hildenbrand (Arm), Jason Wang, Xuan Zhuo,
Eugenio Pérez, Muchun Song, Oscar Salvador, Andrew Morton,
Lorenzo Stoakes, Liam R. Howlett, Vlastimil Babka, Mike Rapoport,
Suren Baghdasaryan, Michal Hocko, Brendan Jackman,
Johannes Weiner, Zi Yan, Baolin Wang, Nico Pache, Ryan Roberts,
Dev Jain, Barry Song, Lance Yang, Hugh Dickins, Matthew Brost,
Joshua Hahn, Rakie Kim, Byungchul Park, Gregory Price, Ying Huang,
Alistair Popple, Christoph Lameter, David Rientjes,
Roman Gushchin, Harry Yoo, Axel Rasmussen, Yuanchu Xie, Wei Xu,
Chris Li, Kairui Song, Kemeng Shi, Nhat Pham, Baoquan He,
virtualization, linux-mm, Andrea Arcangeli
In-Reply-To: <cover.1780906288.git.mst@redhat.com>
In __free_pages_prepare(), when FPI_ZEROED is set the page is already
known to be zero. We can skip kernel_init_pages() if page poisoning is
not enabled (because poison would overwrite the zeroes).
This avoids redundant zeroing work when freeing pages that are already
known to contain all zeros.
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Assisted-by: Claude:claude-opus-4-6
---
mm/page_alloc.c | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 008f1a311c40..e3a7c40c769c 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1443,7 +1443,14 @@ __always_inline bool __free_pages_prepare(struct page *page,
if (kasan_has_integrated_init())
init = false;
}
- if (init)
+ /*
+ * Skip redundant zeroing when the page is already known-zero
+ * (FPI_ZEROED) and page poisoning did not overwrite it.
+ * When page_poisoning is enabled, kernel_poison_pages above
+ * wrote PAGE_POISON (0xAA), so we must re-zero.
+ */
+ if (init && !((fpi_flags & FPI_ZEROED) &&
+ !page_poisoning_enabled_static()))
kernel_init_pages(page, 1 << order);
/*
--
MST
^ permalink raw reply related
* [PATCH v10 22/37] mm: add free_frozen_pages_zeroed
From: Michael S. Tsirkin @ 2026-06-08 8:38 UTC (permalink / raw)
To: linux-kernel
Cc: David Hildenbrand (Arm), Jason Wang, Xuan Zhuo,
Eugenio Pérez, Muchun Song, Oscar Salvador, Andrew Morton,
Lorenzo Stoakes, Liam R. Howlett, Vlastimil Babka, Mike Rapoport,
Suren Baghdasaryan, Michal Hocko, Brendan Jackman,
Johannes Weiner, Zi Yan, Baolin Wang, Nico Pache, Ryan Roberts,
Dev Jain, Barry Song, Lance Yang, Hugh Dickins, Matthew Brost,
Joshua Hahn, Rakie Kim, Byungchul Park, Gregory Price, Ying Huang,
Alistair Popple, Christoph Lameter, David Rientjes,
Roman Gushchin, Harry Yoo, Axel Rasmussen, Yuanchu Xie, Wei Xu,
Chris Li, Kairui Song, Kemeng Shi, Nhat Pham, Baoquan He,
virtualization, linux-mm, Andrea Arcangeli
In-Reply-To: <cover.1780906288.git.mst@redhat.com>
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.
__SetPageZeroed is non-atomic but safe here: the page is frozen
(refcount 0) and not yet on any free list.
Note: when want_init_on_free() zeroes the page via
kernel_init_pages(), the page is zero but the direct-map
cache lines may be dirty. A later patch (skip
kernel_init_pages for FPI_ZEROED) avoids the redundant
re-zero, and post_alloc_hook handles the dcache flush
for user pages on aliasing architectures.
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 | 23 ++++++++++++++++++++++-
3 files changed, 24 insertions(+), 1 deletion(-)
diff --git a/include/linux/gfp.h b/include/linux/gfp.h
index 73109d4e31a4..d24b61e45861 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 4af5e72742ba..fd910743ddc3 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -938,6 +938,7 @@ 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 21f9e92922f1..008f1a311c40 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -91,6 +91,13 @@ 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 +1603,12 @@ 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)) {
+ /* Don't mark zeroed if poison overwrote with 0xAA. */
+ if ((fpi_flags & FPI_ZEROED) && !page_poisoning_enabled_static())
+ __SetPageZeroed(page);
free_one_page(zone, page, pfn, order, fpi_flags);
+ }
}
void __meminit __free_pages_core(struct page *page, unsigned int order,
@@ -3020,6 +3031,10 @@ static void __free_frozen_pages(struct page *page, unsigned int order,
if (!__free_pages_prepare(page, order, fpi_flags))
return;
+ /* Don't mark zeroed if poison overwrote with 0xAA. */
+ if ((fpi_flags & FPI_ZEROED) && !page_poisoning_enabled_static())
+ __SetPageZeroed(page);
+
/*
* We only track unmovable, reclaimable and movable on pcp lists.
* Place ISOLATE pages on the isolated list because they are being
@@ -3058,6 +3073,12 @@ 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
^ permalink raw reply related
* [PATCH v10 21/37] mm: page_alloc: propagate PG_zeroed in split_large_buddy
From: Michael S. Tsirkin @ 2026-06-08 8:38 UTC (permalink / raw)
To: linux-kernel
Cc: David Hildenbrand (Arm), Jason Wang, Xuan Zhuo,
Eugenio Pérez, Muchun Song, Oscar Salvador, Andrew Morton,
Lorenzo Stoakes, Liam R. Howlett, Vlastimil Babka, Mike Rapoport,
Suren Baghdasaryan, Michal Hocko, Brendan Jackman,
Johannes Weiner, Zi Yan, Baolin Wang, Nico Pache, Ryan Roberts,
Dev Jain, Barry Song, Lance Yang, Hugh Dickins, Matthew Brost,
Joshua Hahn, Rakie Kim, Byungchul Park, Gregory Price, Ying Huang,
Alistair Popple, Christoph Lameter, David Rientjes,
Roman Gushchin, Harry Yoo, Axel Rasmussen, Yuanchu Xie, Wei Xu,
Chris Li, Kairui Song, Kemeng Shi, Nhat Pham, Baoquan He,
virtualization, linux-mm, Andrea Arcangeli
In-Reply-To: <cover.1780906288.git.mst@redhat.com>
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>
Reviewed-by: Gregory Price <gourry@gourry.net>
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 7a6dedd716e2..21f9e92922f1 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1520,6 +1520,7 @@ static void split_large_buddy(struct zone *zone, struct page *page,
bool reported)
{
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! */
@@ -1531,6 +1532,8 @@ 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);
if (reported && PageBuddy(page) && buddy_order(page) == order)
__SetPageReported(page);
--
MST
^ permalink raw reply related
* [PATCH v10 20/37] mm: page_alloc: preserve PG_zeroed in page_del_and_expand
From: Michael S. Tsirkin @ 2026-06-08 8:38 UTC (permalink / raw)
To: linux-kernel
Cc: David Hildenbrand (Arm), Jason Wang, Xuan Zhuo,
Eugenio Pérez, Muchun Song, Oscar Salvador, Andrew Morton,
Lorenzo Stoakes, Liam R. Howlett, Vlastimil Babka, Mike Rapoport,
Suren Baghdasaryan, Michal Hocko, Brendan Jackman,
Johannes Weiner, Zi Yan, Baolin Wang, Nico Pache, Ryan Roberts,
Dev Jain, Barry Song, Lance Yang, Hugh Dickins, Matthew Brost,
Joshua Hahn, Rakie Kim, Byungchul Park, Gregory Price, Ying Huang,
Alistair Popple, Christoph Lameter, David Rientjes,
Roman Gushchin, Harry Yoo, Axel Rasmussen, Yuanchu Xie, Wei Xu,
Chris Li, Kairui Song, Kemeng Shi, Nhat Pham, Baoquan He,
virtualization, linux-mm, Andrea Arcangeli
In-Reply-To: <cover.1780906288.git.mst@redhat.com>
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>
Reviewed-by: Gregory Price <gourry@gourry.net>
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 a90bca5317c1..7a6dedd716e2 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);
}
@@ -2355,11 +2360,12 @@ 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
^ permalink raw reply related
* [PATCH v10 19/37] mm: page_alloc: clear PG_zeroed on buddy merge if not both zero
From: Michael S. Tsirkin @ 2026-06-08 8:38 UTC (permalink / raw)
To: linux-kernel
Cc: David Hildenbrand (Arm), Jason Wang, Xuan Zhuo,
Eugenio Pérez, Muchun Song, Oscar Salvador, Andrew Morton,
Lorenzo Stoakes, Liam R. Howlett, Vlastimil Babka, Mike Rapoport,
Suren Baghdasaryan, Michal Hocko, Brendan Jackman,
Johannes Weiner, Zi Yan, Baolin Wang, Nico Pache, Ryan Roberts,
Dev Jain, Barry Song, Lance Yang, Hugh Dickins, Matthew Brost,
Joshua Hahn, Rakie Kim, Byungchul Park, Gregory Price, Ying Huang,
Alistair Popple, Christoph Lameter, David Rientjes,
Roman Gushchin, Harry Yoo, Axel Rasmussen, Yuanchu Xie, Wei Xu,
Chris Li, Kairui Song, Kemeng Shi, Nhat Pham, Baoquan He,
virtualization, linux-mm, Andrea Arcangeli
In-Reply-To: <cover.1780906288.git.mst@redhat.com>
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>
Reviewed-by: Gregory Price <gourry@gourry.net>
Assisted-by: Claude:claude-opus-4-6
Assisted-by: cursor-agent:GPT-5.4-xhigh
---
include/linux/page-flags.h | 1 +
mm/page_alloc.c | 15 ++++++++++++++-
2 files changed, 15 insertions(+), 1 deletion(-)
diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index 91f8ddb1d512..9365d59ac1d6 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -680,6 +680,7 @@ FOLIO_FLAG_FALSE(idle)
* uses this to skip redundant zeroing in post_alloc_hook().
*/
__PAGEFLAG(Zeroed, zeroed, PF_NO_COMPOUND)
+CLEARPAGEFLAG(Zeroed, zeroed, PF_NO_COMPOUND)
#define __PG_ZEROED (1UL << PG_zeroed)
/*
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index edfc83571985..a90bca5317c1 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -941,10 +941,14 @@ 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);
@@ -979,6 +983,8 @@ 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.
@@ -997,10 +1003,17 @@ 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
^ permalink raw reply related
* [PATCH v10 18/37] mm: page_alloc: use aliasing checks instead of user_alloc_needs_zeroing
From: Michael S. Tsirkin @ 2026-06-08 8:38 UTC (permalink / raw)
To: linux-kernel
Cc: David Hildenbrand (Arm), Jason Wang, Xuan Zhuo,
Eugenio Pérez, Muchun Song, Oscar Salvador, Andrew Morton,
Lorenzo Stoakes, Liam R. Howlett, Vlastimil Babka, Mike Rapoport,
Suren Baghdasaryan, Michal Hocko, Brendan Jackman,
Johannes Weiner, Zi Yan, Baolin Wang, Nico Pache, Ryan Roberts,
Dev Jain, Barry Song, Lance Yang, Hugh Dickins, Matthew Brost,
Joshua Hahn, Rakie Kim, Byungchul Park, Gregory Price, Ying Huang,
Alistair Popple, Christoph Lameter, David Rientjes,
Roman Gushchin, Harry Yoo, Axel Rasmussen, Yuanchu Xie, Wei Xu,
Chris Li, Kairui Song, Kemeng Shi, Nhat Pham, Baoquan He,
virtualization, linux-mm, Andrea Arcangeli
In-Reply-To: <cover.1780906288.git.mst@redhat.com>
Replace user_alloc_needs_zeroing() with the direct aliasing checks
(cpu_dcache_is_aliasing() || cpu_icache_is_aliasing()) in the
post_alloc_hook aliasing guard.
user_alloc_needs_zeroing() includes a !init_on_alloc term that
means "allocator didn't zero this page." But in this guard's
context (!zeroed && !init && __GFP_ZERO), we already know the page
is zero; init incorporates init_on_alloc via want_init_on_alloc().
The only question left is whether the cache architecture needs
the data re-zeroed through a congruent mapping, which is purely
cpu_dcache_is_aliasing() || cpu_icache_is_aliasing().
On non-aliasing architectures with init_on_free=true and
init_on_alloc=false, this avoids a redundant re-zero of an
already-zero page.
Note on PowerPC: PowerPC overrides clear_user_page to call
flush_dcache_page after clear_page, but on freshly allocated
pages PG_dcache_clean is already clear (cleared by
__free_pages_prepare), so flush_dcache_page is a no-op.
Skipping this here thus has no effect.
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Assisted-by: Claude:claude-opus-4-6
---
mm/page_alloc.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 45e824b1ec75..edfc83571985 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1880,7 +1880,7 @@ inline void post_alloc_hook(struct page *page, unsigned int order,
*/
if (!zeroed && !init && (gfp_flags & __GFP_ZERO) &&
user_addr != USER_ADDR_NONE &&
- user_alloc_needs_zeroing())
+ (cpu_dcache_is_aliasing() || cpu_icache_is_aliasing()))
init = true;
/*
* If memory is still not initialized, initialize it now.
--
MST
^ permalink raw reply related
* [PATCH v10 17/37] mm: page_reporting: skip redundant zeroing of host-zeroed reported pages
From: Michael S. Tsirkin @ 2026-06-08 8:37 UTC (permalink / raw)
To: linux-kernel
Cc: David Hildenbrand (Arm), Jason Wang, Xuan Zhuo,
Eugenio Pérez, Muchun Song, Oscar Salvador, Andrew Morton,
Lorenzo Stoakes, Liam R. Howlett, Vlastimil Babka, Mike Rapoport,
Suren Baghdasaryan, Michal Hocko, Brendan Jackman,
Johannes Weiner, Zi Yan, Baolin Wang, Nico Pache, Ryan Roberts,
Dev Jain, Barry Song, Lance Yang, Hugh Dickins, Matthew Brost,
Joshua Hahn, Rakie Kim, Byungchul Park, Gregory Price, Ying Huang,
Alistair Popple, Christoph Lameter, David Rientjes,
Roman Gushchin, Harry Yoo, Axel Rasmussen, Yuanchu Xie, Wei Xu,
Chris Li, Kairui Song, Kemeng Shi, Nhat Pham, Baoquan He,
virtualization, linux-mm, Andrea Arcangeli
In-Reply-To: <cover.1780906288.git.mst@redhat.com>
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.
Currently the PG_zeroed hint can be lost when pages are
split (expand) or merged in the buddy allocator. This is
harmless: losing the hint just means the page gets re-zeroed,
which is correct but suboptimal. Follow-up patches propagate
PG_zeroed across splits and merges to preserve the hint on
common paths.
No driver sets host_zeroes_pages yet; a follow-up patch to
virtio_balloon is needed to opt in.
PG_zeroed pages may pass through PCP lists before being freed.
This is safe: __free_pages_prepare clears all
PAGE_FLAGS_CHECK_AT_PREP flags (including PG_zeroed/PG_private)
before the page re-enters the buddy allocator.
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 | 68 +++++++++++++++++++++++-----------
mm/page_reporting.c | 14 ++++++-
mm/page_reporting.h | 12 ++++++
7 files changed, 88 insertions(+), 26 deletions(-)
diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index 7223f6f4e2b4..91f8ddb1d512 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 4336e433c99b..8000fc5e0a2e 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;
}
@@ -1849,9 +1850,10 @@ static struct folio *compaction_alloc_noprof(struct folio *src, unsigned long da
set_page_private(&freepage[size], start_order);
}
dst = (struct folio *)freepage;
+ __ClearPageZeroed(&dst->page);
if (order)
prep_compound_page(&dst->page, order);
- post_alloc_hook(&dst->page, order, __GFP_MOVABLE, USER_ADDR_NONE);
+ post_alloc_hook(&dst->page, order, __GFP_MOVABLE, false, USER_ADDR_NONE);
set_page_refcounted(&dst->page);
cc->nr_freepages -= 1 << order;
cc->nr_migratepages -= 1 << order;
diff --git a/mm/internal.h b/mm/internal.h
index 9d2198114510..4af5e72742ba 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -928,7 +928,7 @@ 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 d4fbf1861a8a..45e824b1ec75 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)
{
const bool zero_tags = gfp_flags & __GFP_ZEROTAGS;
bool init = !want_init_on_free() && want_init_on_alloc(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);
@@ -1867,7 +1878,7 @@ inline void post_alloc_hook(struct page *page, unsigned int order,
* through a user-congruent mapping. Host-zeroed pages
* (zeroed flag) don't need this: physical RAM is clean.
*/
- if (!init && (gfp_flags & __GFP_ZERO) &&
+ if (!zeroed && !init && (gfp_flags & __GFP_ZERO) &&
user_addr != USER_ADDR_NONE &&
user_alloc_needs_zeroing())
init = true;
@@ -1900,13 +1911,13 @@ 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
@@ -3174,6 +3185,7 @@ 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
@@ -3246,7 +3258,7 @@ 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;
@@ -3281,6 +3293,8 @@ 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));
/*
@@ -3349,10 +3363,9 @@ 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;
@@ -3387,6 +3400,8 @@ 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;
@@ -3395,7 +3410,8 @@ 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;
@@ -3413,7 +3429,8 @@ 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);
@@ -3438,19 +3455,19 @@ 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 */
@@ -3841,6 +3858,7 @@ 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;
@@ -3985,10 +4003,11 @@ 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 {
@@ -4215,9 +4234,11 @@ __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)
@@ -5190,6 +5211,7 @@ 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]) {
@@ -5198,7 +5220,7 @@ 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) {
@@ -5209,7 +5231,7 @@ 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;
}
@@ -6949,7 +6971,8 @@ 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;
@@ -7157,8 +7180,9 @@ static int __alloc_contig_frozen_range(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);
+ prep_new_page(head, order, gfp_mask, 0, false, user_addr);
} 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 5b6b17f67131..84ebc4547119 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 */
@@ -390,6 +395,10 @@ 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);
@@ -414,6 +423,9 @@ 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
^ permalink raw reply related
* [PATCH v10 16/37] mm: alloc_swap_folio: pass raw fault address to vma_alloc_folio
From: Michael S. Tsirkin @ 2026-06-08 8:37 UTC (permalink / raw)
To: linux-kernel
Cc: David Hildenbrand (Arm), Jason Wang, Xuan Zhuo,
Eugenio Pérez, Muchun Song, Oscar Salvador, Andrew Morton,
Lorenzo Stoakes, Liam R. Howlett, Vlastimil Babka, Mike Rapoport,
Suren Baghdasaryan, Michal Hocko, Brendan Jackman,
Johannes Weiner, Zi Yan, Baolin Wang, Nico Pache, Ryan Roberts,
Dev Jain, Barry Song, Lance Yang, Hugh Dickins, Matthew Brost,
Joshua Hahn, Rakie Kim, Byungchul Park, Gregory Price, Ying Huang,
Alistair Popple, Christoph Lameter, David Rientjes,
Roman Gushchin, Harry Yoo, Axel Rasmussen, Yuanchu Xie, Wei Xu,
Chris Li, Kairui Song, Kemeng Shi, Nhat Pham, Baoquan He,
virtualization, linux-mm, Andrea Arcangeli
In-Reply-To: <cover.1780906288.git.mst@redhat.com>
Same change as the previous patch but for alloc_swap_folio:
pass vmf->address directly instead of ALIGN_DOWN(vmf->address, ...).
Note: NUMA interleave is not affected by the raw address;
the ilx calculation shifts addr >> PAGE_SHIFT >> order,
dropping sub-page bits regardless of alignment.
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Gregory Price <gourry@gourry.net>
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 21f640674c4f..6c14b90f558e 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -4750,8 +4750,7 @@ 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
^ permalink raw reply related
* [PATCH v10 15/37] mm: alloc_anon_folio: pass raw fault address to vma_alloc_folio
From: Michael S. Tsirkin @ 2026-06-08 8:37 UTC (permalink / raw)
To: linux-kernel
Cc: David Hildenbrand (Arm), Jason Wang, Xuan Zhuo,
Eugenio Pérez, Muchun Song, Oscar Salvador, Andrew Morton,
Lorenzo Stoakes, Liam R. Howlett, Vlastimil Babka, Mike Rapoport,
Suren Baghdasaryan, Michal Hocko, Brendan Jackman,
Johannes Weiner, Zi Yan, Baolin Wang, Nico Pache, Ryan Roberts,
Dev Jain, Barry Song, Lance Yang, Hugh Dickins, Matthew Brost,
Joshua Hahn, Rakie Kim, Byungchul Park, Gregory Price, Ying Huang,
Alistair Popple, Christoph Lameter, David Rientjes,
Roman Gushchin, Harry Yoo, Axel Rasmussen, Yuanchu Xie, Wei Xu,
Chris Li, Kairui Song, Kemeng Shi, Nhat Pham, Baoquan He,
virtualization, linux-mm, Andrea Arcangeli
In-Reply-To: <cover.1780906288.git.mst@redhat.com>
Pass vmf->address directly instead of ALIGN_DOWN(vmf->address, ...).
NUMA interleave is not affected: the ilx calculation in
get_vma_policy() shifts addr >> PAGE_SHIFT >> order, which
drops sub-page bits regardless of alignment. 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>
Reviewed-by: Gregory Price <gourry@gourry.net>
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 86a973119bd4..21f640674c4f 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -5268,8 +5268,7 @@ 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
^ permalink raw reply related
* [PATCH v10 14/37] mm: remove arch vma_alloc_zeroed_movable_folio overrides
From: Michael S. Tsirkin @ 2026-06-08 8:37 UTC (permalink / raw)
To: linux-kernel
Cc: David Hildenbrand (Arm), Jason Wang, Xuan Zhuo,
Eugenio Pérez, Muchun Song, Oscar Salvador, Andrew Morton,
Lorenzo Stoakes, Liam R. Howlett, Vlastimil Babka, Mike Rapoport,
Suren Baghdasaryan, Michal Hocko, Brendan Jackman,
Johannes Weiner, Zi Yan, Baolin Wang, Nico Pache, Ryan Roberts,
Dev Jain, Barry Song, Lance Yang, Hugh Dickins, Matthew Brost,
Joshua Hahn, Rakie Kim, Byungchul Park, Gregory Price, Ying Huang,
Alistair Popple, Christoph Lameter, David Rientjes,
Roman Gushchin, Harry Yoo, Axel Rasmussen, Yuanchu Xie, Wei Xu,
Chris Li, Kairui Song, Kemeng Shi, Nhat Pham, Baoquan He,
virtualization, linux-mm, Andrea Arcangeli, Magnus Lindholm,
Greg Ungerer, Geert Uytterhoeven
In-Reply-To: <cover.1780906288.git.mst@redhat.com>
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>
Assisted-by: Claude:claude-opus-4-6
Reviewed-by: Gregory Price <gourry@gourry.net>
---
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 ---
include/linux/highmem.h | 8 +++++---
5 files changed, 5 insertions(+), 15 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
diff --git a/include/linux/highmem.h b/include/linux/highmem.h
index 8b0afaabbc6e..642718a50c27 100644
--- a/include/linux/highmem.h
+++ b/include/linux/highmem.h
@@ -303,7 +303,6 @@ static inline void clear_user_highpages(struct page *page, unsigned long vaddr,
#endif
}
-#ifndef vma_alloc_zeroed_movable_folio
/**
* vma_alloc_zeroed_movable_folio - Allocate a zeroed page for a VMA.
* @vma: The VMA the page is to be allocated for.
@@ -317,12 +316,15 @@ static inline void clear_user_highpages(struct page *page, unsigned long vaddr,
* we are out of memory.
*/
static inline
-struct folio *vma_alloc_zeroed_movable_folio(struct vm_area_struct *vma,
+struct folio *vma_alloc_zeroed_movable_folio_noprof(struct vm_area_struct *vma,
unsigned long vaddr)
{
- return vma_alloc_folio(GFP_HIGHUSER_MOVABLE | __GFP_ZERO,
+ return vma_alloc_folio_noprof(GFP_HIGHUSER_MOVABLE | __GFP_ZERO,
0, vma, vaddr);
}
+#ifndef vma_alloc_zeroed_movable_folio
+#define vma_alloc_zeroed_movable_folio(...) \
+ alloc_hooks(vma_alloc_zeroed_movable_folio_noprof(__VA_ARGS__))
#endif
static inline void clear_highpage(struct page *page)
--
MST
^ permalink raw reply related
* [PATCH v10 13/37] mm: use __GFP_ZERO in vma_alloc_zeroed_movable_folio
From: Michael S. Tsirkin @ 2026-06-08 8:36 UTC (permalink / raw)
To: linux-kernel
Cc: David Hildenbrand (Arm), Jason Wang, Xuan Zhuo,
Eugenio Pérez, Muchun Song, Oscar Salvador, Andrew Morton,
Lorenzo Stoakes, Liam R. Howlett, Vlastimil Babka, Mike Rapoport,
Suren Baghdasaryan, Michal Hocko, Brendan Jackman,
Johannes Weiner, Zi Yan, Baolin Wang, Nico Pache, Ryan Roberts,
Dev Jain, Barry Song, Lance Yang, Hugh Dickins, Matthew Brost,
Joshua Hahn, Rakie Kim, Byungchul Park, Gregory Price, Ying Huang,
Alistair Popple, Christoph Lameter, David Rientjes,
Roman Gushchin, Harry Yoo, Axel Rasmussen, Yuanchu Xie, Wei Xu,
Chris Li, Kairui Song, Kemeng Shi, Nhat Pham, Baoquan He,
virtualization, linux-mm, Andrea Arcangeli
In-Reply-To: <cover.1780906288.git.mst@redhat.com>
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.
Note: before this series, replacing clear_user_highpage() with
__GFP_ZERO was unsafe on cache-aliasing architectures because
__GFP_ZERO uses clear_page() without a dcache flush. With this
series, it is safe if the caller passes a valid user address
(not USER_ADDR_NONE) to vma_alloc_folio() etc., which delivers
it to post_alloc_hook() for the dcache flush via
folio_zero_user(). It is only unsafe if USER_ADDR_NONE is passed.
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 d7aac9de1c8a..8b0afaabbc6e 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
^ permalink raw reply related
* [PATCH v10 12/37] mm: use folio_zero_user for user pages in post_alloc_hook
From: Michael S. Tsirkin @ 2026-06-08 8:36 UTC (permalink / raw)
To: linux-kernel
Cc: David Hildenbrand (Arm), Jason Wang, Xuan Zhuo,
Eugenio Pérez, Muchun Song, Oscar Salvador, Andrew Morton,
Lorenzo Stoakes, Liam R. Howlett, Vlastimil Babka, Mike Rapoport,
Suren Baghdasaryan, Michal Hocko, Brendan Jackman,
Johannes Weiner, Zi Yan, Baolin Wang, Nico Pache, Ryan Roberts,
Dev Jain, Barry Song, Lance Yang, Hugh Dickins, Matthew Brost,
Joshua Hahn, Rakie Kim, Byungchul Park, Gregory Price, Ying Huang,
Alistair Popple, Christoph Lameter, David Rientjes,
Roman Gushchin, Harry Yoo, Axel Rasmussen, Yuanchu Xie, Wei Xu,
Chris Li, Kairui Song, Kemeng Shi, Nhat Pham, Baoquan He,
virtualization, linux-mm, Andrea Arcangeli
In-Reply-To: <cover.1780906288.git.mst@redhat.com>
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 | 35 ++++++++++++++++++++++++++++++++---
1 file changed, 32 insertions(+), 3 deletions(-)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 4676fd49819e..d4fbf1861a8a 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1861,9 +1861,38 @@ 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);
+ /*
+ * On architectures with cache aliasing, pages zeroed via the
+ * kernel direct map (e.g. init_on_free) must be re-zeroed
+ * through a user-congruent mapping. Host-zeroed pages
+ * (zeroed flag) don't need this: physical RAM is clean.
+ */
+ if (!init && (gfp_flags & __GFP_ZERO) &&
+ user_addr != USER_ADDR_NONE &&
+ user_alloc_needs_zeroing())
+ init = true;
+ /*
+ * 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 relies on folio_nr_pages which
+ * requires __GFP_COMP for order > 0. All user folio
+ * allocations set __GFP_COMP via __folio_alloc.
+ * user_addr != USER_ADDR_NONE implies sleepable
+ * context (user page fault).
+ */
+ VM_WARN_ON_ONCE(order && !(gfp_flags & __GFP_COMP));
+ 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
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