* Re: [PATCH v10 24/37] mm: add put_page_zeroed and folio_put_zeroed
From: David Hildenbrand (Arm) @ 2026-06-08 12:46 UTC (permalink / raw)
To: Lorenzo Stoakes, Michael S. Tsirkin
Cc: linux-kernel, Jason Wang, Xuan Zhuo, Eugenio Pérez,
Muchun Song, Oscar Salvador, Andrew Morton, 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: <aiazXE8pUDeCmP7c@lucifer>
On 6/8/26 14:25, Lorenzo Stoakes wrote:
> On Mon, Jun 08, 2026 at 04:38:54AM -0400, Michael S. Tsirkin wrote:
>> 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.
>
> Do not put comments about specific expected races like this in the commit
> message but not in the code. Subtleties need to be called out.
>
> The commit message also doesn't at all explain why PG_zeroed doesn't
> suffice here.
>
>>
>> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
>> Assisted-by: Claude:claude-opus-4-6
>
> I really don't understand why you have a 'zeroed' folio flag but need to
> also have new API calls to detect that?
>
> They're also HORRIBLY named. Zeroed as in what? Zero page? Huge zero page?
> Memory zeroed by kernel? Pages that userland happen to have zeroed? Or host
> VM zeroed?
>
> Each are cases we address individually and relate to folios.
>
> You absolutely fail to clarify _which one_ you mean, and provide absolutely
> no documentation and add an exported mm API with no description.
>
> This is just I think not something we want to add? Especially on something
> so fundamental?
I raised previously that providing a folio helper is odd, and that I suggested
that we defer this change.
Maybe we'd want to add such an interface for frozen pages later (to be used by
the balloon), but I don't think we want that for folios.
[1] https://lore.kernel.org/all/5f76af6e-9818-42ea-a305-c0fc1d920dca@kernel.org/
--
Cheers,
David
^ permalink raw reply
* Re: [PATCH v10 28/37] mm: hugetlb: add gfp parameter and skip zeroing for zeroed pages
From: Lorenzo Stoakes @ 2026-06-08 12:44 UTC (permalink / raw)
To: Michael S. Tsirkin
Cc: linux-kernel, David Hildenbrand (Arm), Jason Wang, Xuan Zhuo,
Eugenio Pérez, Muchun Song, Oscar Salvador, Andrew Morton,
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: <f251c9e495cdf98169f225559927112103303137.1780906288.git.mst@redhat.com>
On Mon, Jun 08, 2026 at 04:39:26AM -0400, Michael S. Tsirkin wrote:
> 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
This whole set of hugetlb changes should be a separate series. Or really
deferred.
You very badly need to pare this down into the _minimum_ changes required rather
than AI go brrrr on everything.
And propagating _yet more_ 'zeroed' state seems unpleasant, do we have to?
> ---
> 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)
Same comments about this naming as elsewhere. Let's be specific about what
_kind_ of zeroing this is.
>
> #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);
You already started calling into this user_addr stuff in an earlier patch I
believe, so why not rename it then...
> 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)
This zeroed flag seems to be used for both hugetlb zeroed flag state and
__GFP_ZERO?
What does it mean? Can we be specific and comment? Because it's very confusing.
> {
> /*
> * 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 */
Again, please be specific about the kind of zeroing.
> + 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)
_Please_ be specific about hugetlb in newer functions. 'Huge' is very
overloaded.
And again you're doing the pattern of adding various 'zeroed' state, but then
_also_ adding a specific flag for hinting zeroed state.
I don't understand why we need both and you're adding complexity here for that.
> +{
> + __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);
More mystery meat boolean flags.
> 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 */
This comment is redundant and underspecified.
> + if (gfp_mask & __GFP_ZERO)
> + folio_set_hugetlb_zeroed(folio);
So now we're marking zeroed even in cases where it's not the host VM zeroing?
Is this useful?
> +
> 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)
Can we not propagate arbitrary GFP flags if we can avoid it?
> {
> 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 */
Why are you dropping this?
> }
>
> /*
> @@ -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);
So this represents general zeroed state (not just host VM, based on how you set
it above), but you also clear it when you just zeroed the folio? I'm confused.
What does this flag actually mean?
> +
> 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));
Is the !! actually necessary?
> 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.
> + */
Wait what??
Your whole thesis is that USER_ADDR_NONE can never possibly get used, and now
you're guarding against that not being true?
> + folio = alloc_hugetlb_folio(vma, vmf->real_address & PAGE_MASK,
> + false, __GFP_ZERO);
OK so we propagate GFP just for __GFP_ZERO... Can we not?
> 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);
Not loving the '0' on these... Let's find another way to represent that.
> if (IS_ERR(folio)) {
> folio_put(*foliop);
> ret = -ENOMEM;
> --
> MST
>
Thanks, Lorenzo
^ permalink raw reply
* Re: [PATCH v10 27/37] mm: use __GFP_ZERO in vma_alloc_anon_folio_pmd
From: Lorenzo Stoakes @ 2026-06-08 12:32 UTC (permalink / raw)
To: Michael S. Tsirkin
Cc: linux-kernel, David Hildenbrand (Arm), Jason Wang, Xuan Zhuo,
Eugenio Pérez, Muchun Song, Oscar Salvador, Andrew Morton,
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: <2ee827fed4765a155d2b56bb0e13d7ee5fc6dce8.1780906288.git.mst@redhat.com>
On Mon, Jun 08, 2026 at 04:39:18AM -0400, Michael S. Tsirkin wrote:
> 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.
Again, is this worth it?...
Every bit of code added increases risks of bugs, maintenance burden,
etc. let's just not do stuff because we can.
>
> 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);
Same comments as previously.
> 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()
folio zeroing?
> * write.
> */
> __folio_mark_uptodate(folio);
> --
> MST
>
Thanks, Lorenzo
^ permalink raw reply
* Re: [PATCH v10 26/37] mm: vma_alloc_anon_folio_pmd: pass raw fault address to vma_alloc_folio
From: Lorenzo Stoakes @ 2026-06-08 12:30 UTC (permalink / raw)
To: Michael S. Tsirkin
Cc: linux-kernel, David Hildenbrand (Arm), Jason Wang, Xuan Zhuo,
Eugenio Pérez, Muchun Song, Oscar Salvador, Andrew Morton,
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: <94f64aeca62d8419d76f2cf82b36f1da6017a312.1780906288.git.mst@redhat.com>
On Mon, Jun 08, 2026 at 04:39:10AM -0400, Michael S. Tsirkin wrote:
> 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.
But then what's the point in this change?
And why are we changing what we pass in this parameter but not the
vma_alloc_folio() kdoc?
>
> 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
>
Thanks, Lorenzo
^ permalink raw reply
* Re: [PATCH v10 25/37] mm: use __GFP_ZERO in alloc_anon_folio
From: Lorenzo Stoakes @ 2026-06-08 12:29 UTC (permalink / raw)
To: Michael S. Tsirkin
Cc: linux-kernel, David Hildenbrand (Arm), Jason Wang, Xuan Zhuo,
Eugenio Pérez, Muchun Song, Oscar Salvador, Andrew Morton,
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: <13ed2aa6607d510bd8dc6d602e96626511ee4fee.1780906288.git.mst@redhat.com>
On Mon, Jun 08, 2026 at 04:39:02AM -0400, Michael S. Tsirkin wrote:
> 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.
Is this even worth the effort? This is surely not a hotpath...
>
> 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);
You just allocated the folio as zeroed above, should PG_zeroed not be set thus
making it unnecessary to add folio_put_zeroed()?
> 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
>
Thanks, Lorenzo
^ permalink raw reply
* Re: [PATCH v10 24/37] mm: add put_page_zeroed and folio_put_zeroed
From: Lorenzo Stoakes @ 2026-06-08 12:25 UTC (permalink / raw)
To: Michael S. Tsirkin
Cc: linux-kernel, David Hildenbrand (Arm), Jason Wang, Xuan Zhuo,
Eugenio Pérez, Muchun Song, Oscar Salvador, Andrew Morton,
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: <fef7ca7bbf591865defef658b0792b58494aaed5.1780906288.git.mst@redhat.com>
On Mon, Jun 08, 2026 at 04:38:54AM -0400, Michael S. Tsirkin wrote:
> 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.
Do not put comments about specific expected races like this in the commit
message but not in the code. Subtleties need to be called out.
The commit message also doesn't at all explain why PG_zeroed doesn't
suffice here.
>
> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> Assisted-by: Claude:claude-opus-4-6
I really don't understand why you have a 'zeroed' folio flag but need to
also have new API calls to detect that?
They're also HORRIBLY named. Zeroed as in what? Zero page? Huge zero page?
Memory zeroed by kernel? Pages that userland happen to have zeroed? Or host
VM zeroed?
Each are cases we address individually and relate to folios.
You absolutely fail to clarify _which one_ you mean, and provide absolutely
no documentation and add an exported mm API with no description.
This is just I think not something we want to add? Especially on something
so fundamental?
> ---
> 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));
> +}
> +
Please stop adding more APIs to mm without kdocs. This just isn't
acceptable.
> /**
> * 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 */
Please don't add comments about why you didn't do something that nobody
here knows about with no context.
If you want to say something about this, make it clear. This is so succinct
it's utterly meaningless.
> 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);
>
No documentation again...
> +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
>
Thanks, Lorenzo
^ permalink raw reply
* Re: [PATCH v10 23/37] mm: page_alloc: skip kernel_init_pages for FPI_ZEROED when safe
From: Lorenzo Stoakes @ 2026-06-08 12:18 UTC (permalink / raw)
To: Michael S. Tsirkin
Cc: linux-kernel, David Hildenbrand (Arm), Jason Wang, Xuan Zhuo,
Eugenio Pérez, Muchun Song, Oscar Salvador, Andrew Morton,
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: <7de6959a0fb1b255dc9bee2de494f51a6c21e468.1780906288.git.mst@redhat.com>
On Mon, Jun 08, 2026 at 04:38:46AM -0400, Michael S. Tsirkin wrote:
> 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.
> + */
Again, please stop specifying arbitrary hex values in comments, this seems
mostly 'describing what we do here'.
Maybe drop to just e.g.:
/* if poisoned or not zeroed by a virtualised host, zero now. */
or suchlike?
> + if (init && !((fpi_flags & FPI_ZEROED) &&
> + !page_poisoning_enabled_static()))
This condition is absolutely horrible, !(X && !Y), you're making life difficult
for the readers.
'if not both zeroed and not poisoned' is how that reads logically. Which is hard
to understand.
De Morgan's law gives us -> !zeroed || posioned
How about:
if (init && (!(fpi_flags & FPI_ZEROED) || page_poisoning_enabled_static())
Or preferably something like:
const bool poisoned = page_poisoning_enabled_static();
const bool vm_host_zeroed = fpi_flags & FPI_ZEROED;
...
if (init && (poisoned || !vm_host_zeroed))
...
?
> kernel_init_pages(page, 1 << order);
>
> /*
> --
> MST
>
Thanks, Lorenzo
^ permalink raw reply
* Re: [PATCH v10 22/37] mm: add free_frozen_pages_zeroed
From: Lorenzo Stoakes @ 2026-06-08 12:06 UTC (permalink / raw)
To: Michael S. Tsirkin
Cc: linux-kernel, David Hildenbrand (Arm), Jason Wang, Xuan Zhuo,
Eugenio Pérez, Muchun Song, Oscar Salvador, Andrew Morton,
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: <4220116b4d91f3e933fa76ad473106c2e48fd452.1780906288.git.mst@redhat.com>
On Mon, Jun 08, 2026 at 04:38:37AM -0400, Michael S. Tsirkin wrote:
> 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);
This is badly named. That name implies you're freeing frozen, zeroed pages, not
that you're marking them zeroed.
And again, you're overloading 'zeroed' here. Be specific, it's about
host zeroing in virtualisation.
> 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
Can we just be specific that this is about VM hosts, I don't imagine that we are
going to ever have a use beyond that, and we can adjust the phrasing later if
needed.
Otherwise it's just confusing right now, you're overloading 'zeroed' to mean
different things and we do that enough in mm already.
> + * allocation can skip redundant zeroing.
> + */
> +#define FPI_ZEROED ((__force fpi_t)BIT(3))
Hmm now we have another flag to propagate this around... this is messy.
Now we have multiple different ways of representing this state... ugh.
> +
> /* 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. */
Can we not reference arbitrary values in comments? And this comment seems
redundant.
> + 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. */
Same comment as above.
> + 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);
> }
>
No comment describing this? kdoc please.
> +void free_frozen_pages_zeroed(struct page *page, unsigned int order)
> +{
> + __free_frozen_pages(page, order, FPI_ZEROED);
> +}
> +EXPORT_SYMBOL(free_frozen_pages_zeroed);
Do we have to use EXPORT_SYMBOLS()? Why not EXPORT_SYMBOLS_GPL()?
> +
> void free_frozen_pages_nolock(struct page *page, unsigned int order)
> {
> __free_frozen_pages(page, order, FPI_TRYLOCK);
> --
> MST
>
Thanks, Lorenzo
^ permalink raw reply
* Re: [PATCH v10 17/37] mm: page_reporting: skip redundant zeroing of host-zeroed reported pages
From: Lorenzo Stoakes @ 2026-06-08 12:00 UTC (permalink / raw)
To: Michael S. Tsirkin
Cc: linux-kernel, David Hildenbrand (Arm), Jason Wang, Xuan Zhuo,
Eugenio Pérez, Muchun Song, Oscar Salvador, Andrew Morton,
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: <6a2f93e4447e55ada6ccf0f4d5c64e8d41a848d4.1780906288.git.mst@redhat.com>
On Mon, Jun 08, 2026 at 04:37:48AM -0400, Michael S. Tsirkin wrote:
> 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.
I think this flag is really confusingly named, if it's a virtualised host
thing, then can we please encode that in the flag name?
I was looking at a later commit and wondering who was doing the zeroing
exactly.
And could we please propagate that throughout the code, some nebulous 'bool
zeroed = ... ' begs the question of whether it's the kernel who did it and
why we are adding logic
>
> - 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);
host_zeroed or something would be more appropriate no?
But in general do we need to propagate this around, can't we derive it from
the page zeroed flag?
It's really confusing as to _which_ zeroing this refers to, it seems the
only one relevant here is the VM host zeroing but that's completely
non-obvious and now everybody using these functions with the extra param
will simply have to happen to know this.
If we could find a way to avoid this propagation that'd be ideal.
Failing that, making it clear this is _only_ for vm host zeroing would be
better, but then maybe we need to think about how we could encode this in
some other way, e.g. passing alloc_context perhaps?
> 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);
> +
Stray whitespace?
> 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);
> }
>
> +
Stray whitespace?
> 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);
A nit but I really hate these kinds of mystery meat booleans, which mean
you have to now go look up what this is.
One thing we use in mm quite a bit now is e.g. '/*zeroed=*/ false'. Though
some might say even having a boolean like this is a code smell in itself.
> } 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
>
Thanks, Lorenzo
^ permalink raw reply
* Re: [PATCH v10 19/37] mm: page_alloc: clear PG_zeroed on buddy merge if not both zero
From: Lorenzo Stoakes @ 2026-06-08 11:47 UTC (permalink / raw)
To: Michael S. Tsirkin
Cc: linux-kernel, David Hildenbrand (Arm), Jason Wang, Xuan Zhuo,
Eugenio Pérez, Muchun Song, Oscar Salvador, Andrew Morton,
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: <918897302a4cab9f476625adc238ec65a688d1d7.1780906288.git.mst@redhat.com>
On Mon, Jun 08, 2026 at 04:38:08AM -0400, Michael S. Tsirkin wrote:
> 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 &
NIT: We don't add new VM_BUG_ON()'s, please use VM_WARN_ON().
> + (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
* Re: [PATCH v10 18/37] mm: page_alloc: use aliasing checks instead of user_alloc_needs_zeroing
From: Lorenzo Stoakes @ 2026-06-08 11:39 UTC (permalink / raw)
To: Michael S. Tsirkin
Cc: linux-kernel, David Hildenbrand (Arm), Jason Wang, Xuan Zhuo,
Eugenio Pérez, Muchun Song, Oscar Salvador, Andrew Morton,
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: <d9b5fc983725665749024312f9ff5ede4f05e405.1780906288.git.mst@redhat.com>
On Mon, Jun 08, 2026 at 04:38:00AM -0400, Michael S. Tsirkin wrote:
> 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
This seems like an odd ordering of patches, can we group like changes
together?
> ---
> 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()))
Let's try and simplify things rather than adding endlessly huge if conditionals?
It's now incredibly hard to track exactly what's going on here, and that is
bug-bait.
> init = true;
> /*
> * If memory is still not initialized, initialize it now.
> --
> MST
>
Thanks, Lorenzo
^ permalink raw reply
* Re: [PATCH v10 16/37] mm: alloc_swap_folio: pass raw fault address to vma_alloc_folio
From: Lorenzo Stoakes @ 2026-06-08 11:37 UTC (permalink / raw)
To: Michael S. Tsirkin
Cc: linux-kernel, David Hildenbrand (Arm), Jason Wang, Xuan Zhuo,
Eugenio Pérez, Muchun Song, Oscar Salvador, Andrew Morton,
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: <d2be78654e9dcc7cf5b8a542c2c8f331187c80c9.1780906288.git.mst@redhat.com>
On Mon, Jun 08, 2026 at 04:37:41AM -0400, Michael S. Tsirkin wrote:
> Same change as the previous patch but for alloc_swap_folio:
Please don't say 'same change as the previous patch' :) explain what you're
doing here. It's a pain to have to go check otherwise.
> 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.
You're expressing the same thing as the last patch differently, but then
eliding other explanations from that?
All the same questions as I asked for the last apply to this also.
And also - if you've now made this a _requirement_ that is broken
otherwise, then aren't these bisection hazards and should be squashed into
the change?...
No patch should break anything at any point.
>
> 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
>
Thanks, Lorenzo
^ permalink raw reply
* Re: [PATCH v10 15/37] mm: alloc_anon_folio: pass raw fault address to vma_alloc_folio
From: Lorenzo Stoakes @ 2026-06-08 11:35 UTC (permalink / raw)
To: Michael S. Tsirkin
Cc: linux-kernel, David Hildenbrand (Arm), Jason Wang, Xuan Zhuo,
Eugenio Pérez, Muchun Song, Oscar Salvador, Andrew Morton,
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: <2e931dc3daa76b57eaedd5b2d3d49f1075797252.1780906288.git.mst@redhat.com>
On Mon, Jun 08, 2026 at 04:37:25AM -0400, Michael S. Tsirkin wrote:
> 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().
I'm confused as to the justification for this? You're saying 'make change X,
it's safe because Y'. So the justification is now this post_alloc_hook thing.
But are you now creating a new requirement of vma_alloc_folio() that you must
specify the actual address we are faulting on, not an address within the folio
or the folio's base address?
(If that's a requirement, why is it?)
If so you should update the vma_alloc_folio() description 'virtual address of
the allocation' is not at all clear.
And if that _is_ a requirement, then are you sure all allocation paths are
correct?
I already see addr & HPAGE_PMD_MASK in vma_alloc_anon_folio_pmd() for
instance?
If it's not a requirement, why are we doing this? it's surely useless in
that case?
>
> 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);
If you're removing this usage, could you also remove the silly thing of us
declaring this at function scope then using it in branches when we should always
have declared these separately?
> - 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
>
Thanks, Lorenzo
^ permalink raw reply
* Re: [PATCH v10 14/37] mm: remove arch vma_alloc_zeroed_movable_folio overrides
From: Lorenzo Stoakes @ 2026-06-08 11:29 UTC (permalink / raw)
To: Michael S. Tsirkin
Cc: linux-kernel, David Hildenbrand (Arm), Jason Wang, Xuan Zhuo,
Eugenio Pérez, Muchun Song, Oscar Salvador, Andrew Morton,
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: <c374d7a35a35eb4bd5ed85f87ff6885fae605fa9.1780906288.git.mst@redhat.com>
On Mon, Jun 08, 2026 at 04:37:08AM -0400, Michael S. Tsirkin wrote:
> 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
We're specifying this function unconditionally even though arm64 overrides?
> /**
> * 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);
This whole change seems unnecessary?
> }
> +#ifndef vma_alloc_zeroed_movable_folio
> +#define vma_alloc_zeroed_movable_folio(...) \
> + alloc_hooks(vma_alloc_zeroed_movable_folio_noprof(__VA_ARGS__))
> #endif
I don't know why we need to add more of this alloc_hooks() dance when we could
just do:
#define vma_alloc_zeroed_movable_folio(vma, vaddr) \
vma_alloc_folio(GFP_HIGHUSER_MOVABLE | __GFP_ZERO, 0, vma, vaddr)
Like the existing arch stuff?
>
> static inline void clear_highpage(struct page *page)
> --
> MST
>
Thanks, Lorenzo
^ permalink raw reply
* Re: [PATCH v10 12/37] mm: use folio_zero_user for user pages in post_alloc_hook
From: Lorenzo Stoakes @ 2026-06-08 11:23 UTC (permalink / raw)
To: Michael S. Tsirkin
Cc: linux-kernel, David Hildenbrand (Arm), Jason Wang, Xuan Zhuo,
Eugenio Pérez, Muchun Song, Oscar Salvador, Andrew Morton,
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: <f92f6f06e5804b4ea7f68b8664b7e69953b50f4e.1780906288.git.mst@redhat.com>
On Mon, Jun 08, 2026 at 04:36:38AM -0400, Michael S. Tsirkin wrote:
> 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())
We check this (gfp_flags & __GFP_ZERO) && user_addr != USER_ADDR_NONE thing
twice, can we just put in a 'init_should_folio_zero' const bool or something?
> + init = true;
As Vlasta says not sure if we want to add complexity just for these arches.
> + /*
> + * If memory is still not initialized, initialize it now.
I kinda hate that 'init' is unclear as to 'do init' or 'was init somewhere
else'... Anwyay.
> + * 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.
This whole paragraph seems pretty useless and just describing the code?
> + */
> + 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.
This whole paragraph is useless and very like the kind of stuff AI generates for
comments, i.e. overly long + entirely unnecessary stuff.
> + * user_addr != USER_ADDR_NONE implies sleepable
> + * context (user page fault).
Can you safely assume that? Also inferring which context we are in from this
parameter seems risky.
It seems to me that you're now making it such that kernel developers:
- Have to know when and when not to specify a user address, and under what
circumstances we might consider that to be mapped.
- Need to know to do this correctly for aliasing architectures or have silent
correctness issues.
- Need to take context into account when specifying this.
We definitely need to find a simpler way to do this!
> + */
> + VM_WARN_ON_ONCE(order && !(gfp_flags & __GFP_COMP));
Surely by now we can assume this?
> + folio_zero_user(page_folio(page), user_addr);
> + } else
> + kernel_init_pages(page, 1 << order);
I hate this hanging else branch... definitely prefer {} on both branches.
But in any case it seems like we could avoid some indentation with something
like:
if (init && init_should_folio_zero) {
...
} else if (init) {
...
}
Or even a:
if (!init)
goto out;
And stick an out label below?
> + }
>
> set_page_owner(page, order, gfp_flags);
> page_table_check_alloc(page, order);
> --
> MST
>
Oh and in general it seems that this conflicts with [0] which removes
kernel_init_pages().
[0];https://lore.kernel.org/all/20260422102729.166599-1-hsalunke@amd.com/
Thanks, Lorenzo
^ permalink raw reply
* Re: [PATCH v10 00/37] mm/virtio: skip redundant zeroing of host-zeroed pages
From: Vlastimil Babka (SUSE) @ 2026-06-08 11:13 UTC (permalink / raw)
To: Michael S. Tsirkin, linux-kernel
Cc: David Hildenbrand (Arm), Jason Wang, Xuan Zhuo,
Eugenio Pérez, Muchun Song, Oscar Salvador, Andrew Morton,
Lorenzo Stoakes, Liam R. Howlett, 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: <8d5d2fa3-a60c-4d04-b3bf-7a8fe89cb1a0@kernel.org>
On 6/8/26 13:02, Vlastimil Babka (SUSE) wrote:
> On 6/8/26 10:33, Michael S. Tsirkin wrote:
>> Further, on architectures with aliasing caches, upstream with init_on_alloc
>
> It seems those are niche architectures so we can ignore that part for perf
> purposes; the other reason why user_alloc_needs_zeroing() would be true is
> booting with init_on_alloc.
OK I misread how user_alloc_needs_zeroing() works wrt init_on_alloc, as it's
negated. But you're changing that anyway to skip that user zeroing, right?
"
This series eliminates that double-zeroing by moving the zeroing
into the post_alloc_hook + propagating the "host
already zeroed this page" information through the buddy allocator.
"
So relying on "everything in buddy is zeroed" would still work I'd think.
>> double-zeros user pages: once via kernel_init_pages() in
>> post_alloc_hook, and again via clear_user_highpage() at the
>> callsite (because user_alloc_needs_zeroing() returns true).
>> This series eliminates that double-zeroing by moving the zeroing
>> into the post_alloc_hook + propagating the "host
>> already zeroed this page" information through the buddy allocator.
>
> I wonder if this whole thing would be much easier if those that would want
> performance would enable only init_on_free and not init_on_alloc at the same
> time. If you enable both you're paranoid and just eat the cost I guess. Then
> you're maybe also paranoid so much that you wouldn't want to trust the host
> zeroing anyway?
>
> post_alloc_hook() already has logic that if init_on_free is enabled, there's
> no init during alloc. So then I think you would only need to communicate
> that host zeroed some pages when the guest adds them to the buddy allocator,
> and that's it?
>
> I.e. if we can just assume that everything in the buddy is zeroed, we don't
> need all the PG_zero flag and whatnot complexity.
^ permalink raw reply
* Re: [PATCH v10 36/37] mm: balloon: use put_page_zeroed for zeroed balloon pages
From: David Hildenbrand (Arm) @ 2026-06-08 11:10 UTC (permalink / raw)
To: Michael S. Tsirkin, linux-kernel
Cc: 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: <619342ca2c01c60862fe49cd4a790d171cd65ef3.1780906288.git.mst@redhat.com>
On 6/8/26 10:40, Michael S. Tsirkin wrote:
> 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;
> }
I think I raised previously that this is best done later.
This patch set is currently trying to do too many things, and is on the larger
side. I think we should try to reduce it to the bare minimum and get some
agreement between maintainers on the core design.
--
Cheers,
David
^ permalink raw reply
* Re: [PATCH v10 07/37] mm: thread user_addr through page allocator for cache-friendly zeroing
From: David Hildenbrand (Arm) @ 2026-06-08 11:08 UTC (permalink / raw)
To: Lorenzo Stoakes, Michael S. Tsirkin
Cc: linux-kernel, Jason Wang, Xuan Zhuo, Eugenio Pérez,
Muchun Song, Oscar Salvador, Andrew Morton, 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: <aiaUDTeHDA45ZXFS@lucifer>
On 6/8/26 12:23, Lorenzo Stoakes wrote:
> I noticed this patch, again, sneaks in some additional code changes that
> are not mentioned in the commit message and seem irrelevant to the patch.
>
> Not sure if the AI is doing this, but please don't do that.
>
> On Mon, Jun 08, 2026 at 04:35:17AM -0400, Michael S. Tsirkin wrote:
>> Thread a user virtual address from vma_alloc_folio() down through
>> the page allocator to post_alloc_hook(). This is plumbing
>> preparation for a subsequent patch that will use user_addr to
>> call folio_zero_user() for cache-friendly zeroing of user pages.
>
> This feels like very weak justification for code that massively changes mm
> code and makes it all much worse.
>
>>
>> The user_addr is stored in struct alloc_context and flows through:
>> vma_alloc_folio -> folio_alloc_mpol -> __alloc_pages_mpol ->
>> __alloc_frozen_pages -> get_page_from_freelist -> prep_new_page ->
>> post_alloc_hook
>
> Is this the only relevant code path? You're changing a TON of code here
> that will have multiple different code paths?
>
>>
>> USER_ADDR_NONE ((unsigned long)-1) is used for non-user
>> allocations, since address 0 is a valid userspace mapping.
>
> Ugh god, so now we're passing a user address through allocation paths that
> might not even be aware of this or be allocating memory at a point when the
> mapping is known?
The original ideas was to do this only with internal interfaces. I think I
raised before to leave hugetlb alone for now.
Fundamentally, user_alloc_needs_zeroing() is something we should get rid of, to
just be able use __GFP_ZERO and do zeroing at exactly one place.
The question is how to pass that information (user_addr) through internal APIs.
I previously said, that ideally we'd end up with a folio allocation interface in
mm/page_alloc.c, from where we could get this done more cleanly internally.
But I don't want what the previous proposals did: use GFP flags+leak state or
return magic "zeroed" flags.
--
Cheers,
David
^ permalink raw reply
* Re: [PATCH v10 07/37] mm: thread user_addr through page allocator for cache-friendly zeroing
From: Lorenzo Stoakes @ 2026-06-08 11:06 UTC (permalink / raw)
To: Michael S. Tsirkin
Cc: linux-kernel, David Hildenbrand (Arm), Jason Wang, Xuan Zhuo,
Eugenio Pérez, Muchun Song, Oscar Salvador, Andrew Morton,
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: <aiaUDTeHDA45ZXFS@lucifer>
In terms of an alternative, I feel that we should:
1. Continue to not change external APIs (correct to not do so)
2. Avoid adding this to any code paths that don't strictly need it
3. Refactor the existing code to make it harder to get wrong. Don't have an
easily confused sentinel, rather have some kind of context state that is
passed through.
I mean we already have alloc_context and you're already updating it :)
But instead of overloading user_addr to indicate all kinds of things, instead
make life easier by actually breaking things out.
Like:
enum alloc_context_type {
KERNEL_ALLOCATION,
USER_MAPPED_ALLOCATION,
USER_UNMAPPED_ALLOCATION, // Maybe? Do we ever?
/* Perhaps some other states we want to encode? */
};
struct alloc_context {
...
enum alloc_context_type type;
unsigned long user_addr; // Only set if type == USER_ALLOCATION
// Maybe something suggesting context or whether we init before in some
// cases?
};
And thread that through?
That way we can also add further context later if required rather than this
awkward easily misunderstood parameter.
It might means some further prepatory patches but it avoids the confusion of not
knowing what to set this to, and could perhaps be set further up the stack?
Then look to completely eliminate cases where we zero other than with
__GFP_ZERO.
Perhaps others have ideas too, but this kind of approach seems more appropriate?
It also seems right to send this work as a entirely separate series. 'Always
zero user memory using __GFP_ZERO' seems like a totally valid independent
series.
Thanks, Lorenzo
^ permalink raw reply
* Re: [PATCH v10 00/37] mm/virtio: skip redundant zeroing of host-zeroed pages
From: Vlastimil Babka (SUSE) @ 2026-06-08 11:02 UTC (permalink / raw)
To: Michael S. Tsirkin, linux-kernel
Cc: David Hildenbrand (Arm), Jason Wang, Xuan Zhuo,
Eugenio Pérez, Muchun Song, Oscar Salvador, Andrew Morton,
Lorenzo Stoakes, Liam R. Howlett, 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>
On 6/8/26 10:33, Michael S. Tsirkin wrote:
> Further, on architectures with aliasing caches, upstream with init_on_alloc
It seems those are niche architectures so we can ignore that part for perf
purposes; the other reason why user_alloc_needs_zeroing() would be true is
booting with init_on_alloc.
> double-zeros user pages: once via kernel_init_pages() in
> post_alloc_hook, and again via clear_user_highpage() at the
> callsite (because user_alloc_needs_zeroing() returns true).
> This series eliminates that double-zeroing by moving the zeroing
> into the post_alloc_hook + propagating the "host
> already zeroed this page" information through the buddy allocator.
I wonder if this whole thing would be much easier if those that would want
performance would enable only init_on_free and not init_on_alloc at the same
time. If you enable both you're paranoid and just eat the cost I guess. Then
you're maybe also paranoid so much that you wouldn't want to trust the host
zeroing anyway?
post_alloc_hook() already has logic that if init_on_free is enabled, there's
no init during alloc. So then I think you would only need to communicate
that host zeroed some pages when the guest adds them to the buddy allocator,
and that's it?
I.e. if we can just assume that everything in the buddy is zeroed, we don't
need all the PG_zero flag and whatnot complexity.
^ permalink raw reply
* Re: [PATCH v10 13/37] mm: use __GFP_ZERO in vma_alloc_zeroed_movable_folio
From: Lorenzo Stoakes @ 2026-06-08 10:55 UTC (permalink / raw)
To: Michael S. Tsirkin
Cc: linux-kernel, David Hildenbrand (Arm), Jason Wang, Xuan Zhuo,
Eugenio Pérez, Muchun Song, Oscar Salvador, Andrew Morton,
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: <aiaau7RIhkJMS_oe@lucifer>
On Mon, Jun 08, 2026 at 11:40:02AM +0100, Lorenzo Stoakes wrote:
> On Mon, Jun 08, 2026 at 04:36:51AM -0400, Michael S. Tsirkin wrote:
> > 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
>
> Wait, so now you're making actual correctness predicated on correctly
> passing the right user address??
>
> > it to post_alloc_hook() for the dcache flush via
> > folio_zero_user(). It is only unsafe if USER_ADDR_NONE is passed.
>
> Yeah, ok I'm beating a dead horse a bit here, but no to this approach.
>
> >
> > 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())
>
> So now we are unconditionally zeroing the pages even if
> !user_alloc_needs_zeroing()? You don't mention this in the commit message
> and it seems like it'll regress performance?
OK sorry I see in 12/37 you do this there instead.
>
> > - clear_user_highpage(&folio->page, vaddr);
> > -
> > - return folio;
> > + return vma_alloc_folio(GFP_HIGHUSER_MOVABLE | __GFP_ZERO,
> > + 0, vma, vaddr);
> > }
> > #endif
> >
> > --
> > MST
> >
>
> Thanks, Lorenzo
^ permalink raw reply
* Re: [PATCH v10 13/37] mm: use __GFP_ZERO in vma_alloc_zeroed_movable_folio
From: Lorenzo Stoakes @ 2026-06-08 10:39 UTC (permalink / raw)
To: Michael S. Tsirkin
Cc: linux-kernel, David Hildenbrand (Arm), Jason Wang, Xuan Zhuo,
Eugenio Pérez, Muchun Song, Oscar Salvador, Andrew Morton,
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: <862a59e98104db76ee3998460bfc55e937c218c4.1780906288.git.mst@redhat.com>
On Mon, Jun 08, 2026 at 04:36:51AM -0400, Michael S. Tsirkin wrote:
> 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
Wait, so now you're making actual correctness predicated on correctly
passing the right user address??
> it to post_alloc_hook() for the dcache flush via
> folio_zero_user(). It is only unsafe if USER_ADDR_NONE is passed.
Yeah, ok I'm beating a dead horse a bit here, but no to this approach.
>
> 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())
So now we are unconditionally zeroing the pages even if
!user_alloc_needs_zeroing()? You don't mention this in the commit message
and it seems like it'll regress performance?
> - clear_user_highpage(&folio->page, vaddr);
> -
> - return folio;
> + return vma_alloc_folio(GFP_HIGHUSER_MOVABLE | __GFP_ZERO,
> + 0, vma, vaddr);
> }
> #endif
>
> --
> MST
>
Thanks, Lorenzo
^ permalink raw reply
* Re: [PATCH v10 11/37] mm: page_alloc: move prep_compound_page before post_alloc_hook
From: Lorenzo Stoakes @ 2026-06-08 10:33 UTC (permalink / raw)
To: Michael S. Tsirkin
Cc: linux-kernel, David Hildenbrand (Arm), Jason Wang, Xuan Zhuo,
Eugenio Pérez, Muchun Song, Oscar Salvador, Andrew Morton,
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: <de0433334a7763b81ce8ca8f8a332c800cfe64ed.1780906288.git.mst@redhat.com>
On Mon, Jun 08, 2026 at 04:36:20AM -0400, Michael S. Tsirkin wrote:
> Move prep_compound_page() before post_alloc_hook() in prep_new_page().
>
> The next patch adds a folio_zero_user() call to post_alloc_hook(),
> which uses folio_nr_pages() to determine how many pages to zero.
> Without compound metadata set up first, folio_nr_pages() returns 1
> for higher-order allocations, so only the first page would be zeroed.
>
> All other operations in post_alloc_hook() (arch_alloc_page, KASAN,
> debug, page owner, etc.) use raw page pointers with explicit order
> counts and are unaffected by this reordering.
I'd put this justification for why this is safe above the 'next patch' stuff.
>
> Also reorder compaction_alloc_noprof() for consistency. Compaction
> currently passes USER_ADDR_NONE so folio_zero_user() is not called
Yeah again, this 'just so' stuff of when or when not an address is passed is
concerning.
> there, but keeping the same ordering avoids a future tripping hazard.
No functional changes or functional changes? If none then say so.
>
> 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
> ---
> mm/compaction.c | 4 ++--
> mm/page_alloc.c | 4 ++--
> 2 files changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/mm/compaction.c b/mm/compaction.c
> index 72684fe81e83..4336e433c99b 100644
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -1849,10 +1849,10 @@ static struct folio *compaction_alloc_noprof(struct folio *src, unsigned long da
> set_page_private(&freepage[size], start_order);
> }
> dst = (struct folio *)freepage;
> - post_alloc_hook(&dst->page, order, __GFP_MOVABLE, USER_ADDR_NONE);
> - set_page_refcounted(&dst->page);
> if (order)
> prep_compound_page(&dst->page, order);
> + post_alloc_hook(&dst->page, order, __GFP_MOVABLE, USER_ADDR_NONE);
> + set_page_refcounted(&dst->page);
> cc->nr_freepages -= 1 << order;
> cc->nr_migratepages -= 1 << order;
> return page_rmappable_folio(&dst->page);
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 0943ab724032..4676fd49819e 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -1874,11 +1874,11 @@ static void prep_new_page(struct page *page, unsigned int order, gfp_t gfp_flags
> unsigned int alloc_flags,
> unsigned long user_addr)
> {
> - post_alloc_hook(page, order, gfp_flags, user_addr);
> -
> if (order && (gfp_flags & __GFP_COMP))
> prep_compound_page(page, order);
>
> + post_alloc_hook(page, order, gfp_flags, user_addr);
> +
> /*
> * page is set pfmemalloc when ALLOC_NO_WATERMARKS was necessary to
> * allocate the page. The expectation is that the caller is taking
> --
> MST
>
Thanks, Lorenzo
^ permalink raw reply
* Re: [PATCH v10 08/37] mm: add alloc_contig_frozen_pages_user for cache-friendly zeroing
From: Lorenzo Stoakes @ 2026-06-08 10:29 UTC (permalink / raw)
To: Michael S. Tsirkin
Cc: linux-kernel, David Hildenbrand (Arm), Jason Wang, Xuan Zhuo,
Eugenio Pérez, Muchun Song, Oscar Salvador, Andrew Morton,
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: <f2036f596f17f66fb55b74a5fd85e8b7ab51876d.1780906288.git.mst@redhat.com>
On Mon, Jun 08, 2026 at 04:35:29AM -0400, Michael S. Tsirkin wrote:
> Add a _user variant of alloc_contig_frozen_pages that accepts a user_addr
> parameter for cache-friendly zeroing of contiguous allocations.
>
> No functional change; all existing callers continue to pass
> USER_ADDR_NONE.
Well, except that you're adding a new function...
>
> Note for reviewers: non-compound contiguous allocations are
Please don't put notes for reviewers in commit messages.
> zeroed via kernel_init_pages, same as before this patch.
> There is no fault address because these allocations are not
> from the page fault path. For compound allocations, user_addr
> reaches post_alloc_hook() which calls folio_zero_user() with
> the dcache flush on cache-aliasing architectures.
Yeah it's exactly this kind of 'just have to know' stuff that makes this
user_addr approach unacceptable.
We mustn't add more cognitive overhead for already confusing code. Now
everybody using these has to figure out what 'user_addr' means and will
inevitably get it wrong.
This whole approach needs to be rethought.
>
> Note about Sashiko (sashiko.dev) false positives: sashiko
> flags two issues here: (1) user_addr silently ignored for
> non-compound allocations, and (2) post_alloc_hook ignores
> user_addr. Both are false positives: (1) non-compound
> contiguous allocations have no fault address to pass, and
> (2) post_alloc_hook does use user_addr when it is not
> USER_ADDR_NONE.
Please don't put AI hallucinations in commit messages.
If you want something to not appear in a commit message, but want reviewers
to see it, put it below the '---' in the patch.
>
> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
This patch is unacceptable for the same reasons given for 7/37.
> Assisted-by: Claude:claude-opus-4-6
> ---
> include/linux/gfp.h | 6 ++++++
> mm/page_alloc.c | 42 ++++++++++++++++++++++++++++++++----------
> 2 files changed, 38 insertions(+), 10 deletions(-)
>
> diff --git a/include/linux/gfp.h b/include/linux/gfp.h
> index ee35c5367abc..73109d4e31a4 100644
> --- a/include/linux/gfp.h
> +++ b/include/linux/gfp.h
> @@ -453,6 +453,12 @@ struct page *alloc_contig_frozen_pages_noprof(unsigned long nr_pages,
> #define alloc_contig_frozen_pages(...) \
> alloc_hooks(alloc_contig_frozen_pages_noprof(__VA_ARGS__))
>
> +struct page *alloc_contig_frozen_pages_user_noprof(unsigned long nr_pages,
> + gfp_t gfp_mask, int nid, nodemask_t *nodemask,
> + unsigned long user_addr);
> +#define alloc_contig_frozen_pages_user(...) \
> + alloc_hooks(alloc_contig_frozen_pages_user_noprof(__VA_ARGS__))
> +
> struct page *alloc_contig_pages_noprof(unsigned long nr_pages, gfp_t gfp_mask,
> int nid, nodemask_t *nodemask);
> #define alloc_contig_pages(...) \
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 21b52c879751..6d3f284c607d 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -6975,13 +6975,15 @@ static void __free_contig_frozen_range(unsigned long pfn, unsigned long nr_pages
> }
>
> /**
> - * alloc_contig_frozen_range() -- tries to allocate given range of frozen pages
> + * __alloc_contig_frozen_range() -- tries to allocate given range of frozen pages
> * @start: start PFN to allocate
> * @end: one-past-the-last PFN to allocate
> * @alloc_flags: allocation information
> * @gfp_mask: GFP mask. Node/zone/placement hints are ignored; only some
> * action and reclaim modifiers are supported. Reclaim modifiers
> * control allocation behavior during compaction/migration/reclaim.
> + * @user_addr: user virtual address for cache-friendly zeroing, or
> + * USER_ADDR_NONE for kernel allocations.
Yeah, I really do not want us passing USER_ADDR_NONE for kernel allocations
thanks. This is hugely confusing already pretty confusing logic.
> *
> * The PFN range does not have to be pageblock aligned. The PFN range must
> * belong to a single zone.
> @@ -6997,8 +6999,9 @@ static void __free_contig_frozen_range(unsigned long pfn, unsigned long nr_pages
> *
> * Return: zero on success or negative error code.
> */
> -int alloc_contig_frozen_range_noprof(unsigned long start, unsigned long end,
> - acr_flags_t alloc_flags, gfp_t gfp_mask)
> +static int __alloc_contig_frozen_range(unsigned long start, unsigned long end,
> + acr_flags_t alloc_flags, gfp_t gfp_mask,
> + unsigned long user_addr)
> {
> const unsigned int order = ilog2(end - start);
> unsigned long outer_start, outer_end;
> @@ -7125,7 +7128,7 @@ int alloc_contig_frozen_range_noprof(unsigned long start, unsigned long end,
> struct page *head = pfn_to_page(start);
>
> check_new_pages(head, order);
> - prep_new_page(head, order, gfp_mask, 0, USER_ADDR_NONE);
> + prep_new_page(head, order, gfp_mask, 0, user_addr);
> } else {
> ret = -EINVAL;
> WARN(true, "PFN range: requested [%lu, %lu), allocated [%lu, %lu)\n",
> @@ -7135,6 +7138,13 @@ int alloc_contig_frozen_range_noprof(unsigned long start, unsigned long end,
> undo_isolate_page_range(start, end);
> return ret;
> }
> +
> +int alloc_contig_frozen_range_noprof(unsigned long start, unsigned long end,
> + acr_flags_t alloc_flags, gfp_t gfp_mask)
> +{
> + return __alloc_contig_frozen_range(start, end, alloc_flags, gfp_mask,
> + USER_ADDR_NONE);
> +}
> EXPORT_SYMBOL(alloc_contig_frozen_range_noprof);
>
> /**
> @@ -7227,14 +7237,16 @@ static bool zone_spans_last_pfn(const struct zone *zone,
> return zone_spans_pfn(zone, last_pfn);
> }
>
> -/**
> - * alloc_contig_frozen_pages() -- tries to find and allocate contiguous range of frozen pages
> +/*
> + * alloc_contig_frozen_pages_user_noprof() -- allocate contiguous frozen pages with user address
> * @nr_pages: Number of contiguous pages to allocate
> * @gfp_mask: GFP mask. Node/zone/placement hints limit the search; only some
> * action and reclaim modifiers are supported. Reclaim modifiers
> * control allocation behavior during compaction/migration/reclaim.
> * @nid: Target node
> * @nodemask: Mask for other possible nodes
> + * @user_addr: user virtual address for cache-friendly zeroing, or
> + * USER_ADDR_NONE for kernel allocations.
> *
> * This routine is a wrapper around alloc_contig_frozen_range(). It scans over
> * zones on an applicable zonelist to find a contiguous pfn range which can then
> @@ -7253,8 +7265,9 @@ static bool zone_spans_last_pfn(const struct zone *zone,
> *
> * Return: pointer to contiguous frozen pages on success, or NULL if not successful.
> */
> -struct page *alloc_contig_frozen_pages_noprof(unsigned long nr_pages,
> - gfp_t gfp_mask, int nid, nodemask_t *nodemask)
> +struct page *alloc_contig_frozen_pages_user_noprof(unsigned long nr_pages,
> + gfp_t gfp_mask, int nid, nodemask_t *nodemask,
> + unsigned long user_addr)
> {
> unsigned long ret, pfn, flags;
> struct zonelist *zonelist;
> @@ -7282,10 +7295,11 @@ struct page *alloc_contig_frozen_pages_noprof(unsigned long nr_pages,
> * win the race and cause allocation to fail.
> */
> spin_unlock_irqrestore(&zone->lock, flags);
> - ret = alloc_contig_frozen_range_noprof(pfn,
> + ret = __alloc_contig_frozen_range(pfn,
> pfn + nr_pages,
> ACR_FLAGS_NONE,
> - gfp_mask);
> + gfp_mask,
> + user_addr);
> if (!ret)
> return pfn_to_page(pfn);
> spin_lock_irqsave(&zone->lock, flags);
> @@ -7307,6 +7321,14 @@ struct page *alloc_contig_frozen_pages_noprof(unsigned long nr_pages,
> }
> return NULL;
> }
> +EXPORT_SYMBOL(alloc_contig_frozen_pages_user_noprof);
Generally we don't add EXPORT_SYMBOL() for new stuff unless
unavoidable. EXPORT_SYMBOL_GPL() is preferred.
> +
> +struct page *alloc_contig_frozen_pages_noprof(unsigned long nr_pages,
> + gfp_t gfp_mask, int nid, nodemask_t *nodemask)
> +{
> + return alloc_contig_frozen_pages_user_noprof(nr_pages, gfp_mask, nid,
> + nodemask, USER_ADDR_NONE);
> +}
> EXPORT_SYMBOL(alloc_contig_frozen_pages_noprof);
>
> /**
> --
> MST
>
Thanks, Lorenzo
^ permalink raw reply
* Re: [PATCH v10 07/37] mm: thread user_addr through page allocator for cache-friendly zeroing
From: Lorenzo Stoakes @ 2026-06-08 10:23 UTC (permalink / raw)
To: Michael S. Tsirkin
Cc: linux-kernel, David Hildenbrand (Arm), Jason Wang, Xuan Zhuo,
Eugenio Pérez, Muchun Song, Oscar Salvador, Andrew Morton,
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: <50d410b47fe3f45327783e05bd306d5eaab75e65.1780906288.git.mst@redhat.com>
I noticed this patch, again, sneaks in some additional code changes that
are not mentioned in the commit message and seem irrelevant to the patch.
Not sure if the AI is doing this, but please don't do that.
On Mon, Jun 08, 2026 at 04:35:17AM -0400, Michael S. Tsirkin wrote:
> Thread a user virtual address from vma_alloc_folio() down through
> the page allocator to post_alloc_hook(). This is plumbing
> preparation for a subsequent patch that will use user_addr to
> call folio_zero_user() for cache-friendly zeroing of user pages.
This feels like very weak justification for code that massively changes mm
code and makes it all much worse.
>
> The user_addr is stored in struct alloc_context and flows through:
> vma_alloc_folio -> folio_alloc_mpol -> __alloc_pages_mpol ->
> __alloc_frozen_pages -> get_page_from_freelist -> prep_new_page ->
> post_alloc_hook
Is this the only relevant code path? You're changing a TON of code here
that will have multiple different code paths?
>
> USER_ADDR_NONE ((unsigned long)-1) is used for non-user
> allocations, since address 0 is a valid userspace mapping.
Ugh god, so now we're passing a user address through allocation paths that
might not even be aware of this or be allocating memory at a point when the
mapping is known?
>
> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Honestly I absolutely hate this patch.
You're passing a user address through allocation paths that might not even
have one associated with them, you're vandalising a bunch of core mm stuff
here for virtio, and then also adding a sentinel to indicate 'not user
address' just to confuse matters further.
We separate the physical allocation of memory from mapping it, and you're
now coupling something that is explicitly decoupled to suit a specific
usecase.
It feels like a hack and I don't think we can accept this upstream, as-is.
> Assisted-by: Claude:claude-opus-4-6
> Assisted-by: cursor-agent:GPT-5.4-xhigh
This really feels like the kind of brute force thing AI does when coming up
with code for this kind of thing.
I think it needs some architectural thought rather than that here. I'd
suggest thinking about how we might achieve the same objective without
doing this.
> ---
> include/linux/gfp.h | 2 +-
> mm/compaction.c | 5 ++---
> mm/hugetlb.c | 36 ++++++++++++++++++++----------------
> mm/internal.h | 21 ++++++++++++++++++---
> mm/mempolicy.c | 44 ++++++++++++++++++++++++++++++++------------
> mm/mmap.c | 6 ++++++
> mm/page_alloc.c | 44 +++++++++++++++++++++++++++++---------------
> mm/slub.c | 4 ++--
> 8 files changed, 110 insertions(+), 52 deletions(-)
>
> diff --git a/include/linux/gfp.h b/include/linux/gfp.h
> index 7ccbda35b9ad..ee35c5367abc 100644
> --- a/include/linux/gfp.h
> +++ b/include/linux/gfp.h
> @@ -337,7 +337,7 @@ static inline struct folio *folio_alloc_noprof(gfp_t gfp, unsigned int order)
> static inline struct folio *folio_alloc_mpol_noprof(gfp_t gfp, unsigned int order,
> struct mempolicy *mpol, pgoff_t ilx, int nid)
> {
> - return folio_alloc_noprof(gfp, order);
> + return __folio_alloc_noprof(gfp, order, numa_node_id(), NULL);
> }
> #endif
>
> diff --git a/mm/compaction.c b/mm/compaction.c
> index 3648ce22c807..72684fe81e83 100644
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -82,7 +82,7 @@ static inline bool is_via_compact_memory(int order) { return false; }
>
> static struct page *mark_allocated_noprof(struct page *page, unsigned int order, gfp_t gfp_flags)
> {
> - post_alloc_hook(page, order, __GFP_MOVABLE);
> + post_alloc_hook(page, order, __GFP_MOVABLE, USER_ADDR_NONE);
This is really confusing. Essentially 'we don't know what the user address
is' here. And now we're making anybody who calls this have to figure out
what the user address field is actually for and under what circumstances we supply it.
> set_page_refcounted(page);
> return page;
> }
> @@ -1849,8 +1849,7 @@ static struct folio *compaction_alloc_noprof(struct folio *src, unsigned long da
> set_page_private(&freepage[size], start_order);
> }
> dst = (struct folio *)freepage;
> -
> - post_alloc_hook(&dst->page, order, __GFP_MOVABLE);
> + post_alloc_hook(&dst->page, order, __GFP_MOVABLE, USER_ADDR_NONE);
> set_page_refcounted(&dst->page);
> if (order)
> prep_compound_page(&dst->page, order);
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 4b80b167cc9c..f3bc15a7889a 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -1786,7 +1786,8 @@ struct address_space *hugetlb_folio_mapping_lock_write(struct folio *folio)
> }
>
> static struct folio *alloc_buddy_frozen_folio(int order, gfp_t gfp_mask,
> - int nid, nodemask_t *nmask, nodemask_t *node_alloc_noretry)
> + int nid, nodemask_t *nmask, nodemask_t *node_alloc_noretry,
> + unsigned long addr)
addr? Can we use user_addr please? This is confusing.
> {
> struct folio *folio;
> bool alloc_try_hard = true;
> @@ -1803,7 +1804,7 @@ static struct folio *alloc_buddy_frozen_folio(int order, gfp_t gfp_mask,
> if (alloc_try_hard)
> gfp_mask |= __GFP_RETRY_MAYFAIL;
>
> - folio = (struct folio *)__alloc_frozen_pages(gfp_mask, order, nid, nmask);
> + folio = (struct folio *)__alloc_frozen_pages(gfp_mask, order, nid, nmask, addr);
>
> /*
> * If we did not specify __GFP_RETRY_MAYFAIL, but still got a
> @@ -1832,7 +1833,7 @@ static struct folio *alloc_buddy_frozen_folio(int order, gfp_t gfp_mask,
>
> static struct folio *only_alloc_fresh_hugetlb_folio(struct hstate *h,
> gfp_t gfp_mask, int nid, nodemask_t *nmask,
> - nodemask_t *node_alloc_noretry)
> + nodemask_t *node_alloc_noretry, unsigned long addr)
> {
> struct folio *folio;
> int order = huge_page_order(h);
> @@ -1844,7 +1845,7 @@ static struct folio *only_alloc_fresh_hugetlb_folio(struct hstate *h,
> folio = alloc_gigantic_frozen_folio(order, gfp_mask, nid, nmask);
> else
> folio = alloc_buddy_frozen_folio(order, gfp_mask, nid, nmask,
> - node_alloc_noretry);
> + node_alloc_noretry, addr);
> if (folio)
> init_new_hugetlb_folio(folio);
> return folio;
> @@ -1858,11 +1859,12 @@ static struct folio *only_alloc_fresh_hugetlb_folio(struct hstate *h,
> * pages is zero, and the accounting must be done in the caller.
> */
> static struct folio *alloc_fresh_hugetlb_folio(struct hstate *h,
> - gfp_t gfp_mask, int nid, nodemask_t *nmask)
> + gfp_t gfp_mask, int nid, nodemask_t *nmask,
> + unsigned long addr)
> {
> struct folio *folio;
>
> - folio = only_alloc_fresh_hugetlb_folio(h, gfp_mask, nid, nmask, NULL);
> + folio = only_alloc_fresh_hugetlb_folio(h, gfp_mask, nid, nmask, NULL, addr);
> if (folio)
> hugetlb_vmemmap_optimize_folio(h, folio);
> return folio;
> @@ -1902,7 +1904,7 @@ static struct folio *alloc_pool_huge_folio(struct hstate *h,
> struct folio *folio;
>
> folio = only_alloc_fresh_hugetlb_folio(h, gfp_mask, node,
> - nodes_allowed, node_alloc_noretry);
> + nodes_allowed, node_alloc_noretry, USER_ADDR_NONE);
> if (folio)
> return folio;
> }
> @@ -2071,7 +2073,8 @@ int dissolve_free_hugetlb_folios(unsigned long start_pfn, unsigned long end_pfn)
> * Allocates a fresh surplus page from the page allocator.
> */
> static struct folio *alloc_surplus_hugetlb_folio(struct hstate *h,
> - gfp_t gfp_mask, int nid, nodemask_t *nmask)
> + gfp_t gfp_mask, int nid, nodemask_t *nmask,
> + unsigned long addr)
Sometimes user_addr, sometimes addr. no thanks.
> {
> struct folio *folio = NULL;
>
> @@ -2083,7 +2086,7 @@ static struct folio *alloc_surplus_hugetlb_folio(struct hstate *h,
> goto out_unlock;
> spin_unlock_irq(&hugetlb_lock);
>
> - folio = alloc_fresh_hugetlb_folio(h, gfp_mask, nid, nmask);
> + folio = alloc_fresh_hugetlb_folio(h, gfp_mask, nid, nmask, addr);
> if (!folio)
> return NULL;
>
> @@ -2126,7 +2129,7 @@ static struct folio *alloc_migrate_hugetlb_folio(struct hstate *h, gfp_t gfp_mas
> if (hstate_is_gigantic(h))
> return NULL;
>
> - folio = alloc_fresh_hugetlb_folio(h, gfp_mask, nid, nmask);
> + folio = alloc_fresh_hugetlb_folio(h, gfp_mask, nid, nmask, USER_ADDR_NONE);
> if (!folio)
> return NULL;
>
> @@ -2162,14 +2165,14 @@ struct folio *alloc_buddy_hugetlb_folio_with_mpol(struct hstate *h,
> if (mpol_is_preferred_many(mpol)) {
> gfp_t gfp = gfp_mask & ~(__GFP_DIRECT_RECLAIM | __GFP_NOFAIL);
>
> - folio = alloc_surplus_hugetlb_folio(h, gfp, nid, nodemask);
> + folio = alloc_surplus_hugetlb_folio(h, gfp, nid, nodemask, addr);
>
> /* Fallback to all nodes if page==NULL */
> nodemask = NULL;
> }
>
> if (!folio)
> - folio = alloc_surplus_hugetlb_folio(h, gfp_mask, nid, nodemask);
> + folio = alloc_surplus_hugetlb_folio(h, gfp_mask, nid, nodemask, addr);
> mpol_cond_put(mpol);
> return folio;
> }
> @@ -2276,7 +2279,8 @@ static int gather_surplus_pages(struct hstate *h, long delta)
> * down the road to pick the current node if that is the case.
> */
> folio = alloc_surplus_hugetlb_folio(h, htlb_alloc_mask(h),
> - NUMA_NO_NODE, &alloc_nodemask);
> + NUMA_NO_NODE, &alloc_nodemask,
> + USER_ADDR_NONE);
> if (!folio) {
> alloc_ok = false;
> break;
> @@ -2682,7 +2686,7 @@ static int alloc_and_dissolve_hugetlb_folio(struct folio *old_folio,
> spin_unlock_irq(&hugetlb_lock);
> gfp_mask = htlb_alloc_mask(h) | __GFP_THISNODE;
> new_folio = alloc_fresh_hugetlb_folio(h, gfp_mask,
> - nid, NULL);
> + nid, NULL, USER_ADDR_NONE);
> if (!new_folio)
> return -ENOMEM;
> goto retry;
> @@ -3380,13 +3384,13 @@ static void __init hugetlb_hstate_alloc_pages_onenode(struct hstate *h, int nid)
> gfp_t gfp_mask = htlb_alloc_mask(h) | __GFP_THISNODE;
>
> folio = only_alloc_fresh_hugetlb_folio(h, gfp_mask, nid,
> - &node_states[N_MEMORY], NULL);
> + &node_states[N_MEMORY], NULL, USER_ADDR_NONE);
> if (!folio && !list_empty(&folio_list) &&
> hugetlb_vmemmap_optimizable_size(h)) {
> prep_and_add_allocated_folios(h, &folio_list);
> INIT_LIST_HEAD(&folio_list);
> folio = only_alloc_fresh_hugetlb_folio(h, gfp_mask, nid,
> - &node_states[N_MEMORY], NULL);
> + &node_states[N_MEMORY], NULL, USER_ADDR_NONE);
> }
> if (!folio)
> break;
> diff --git a/mm/internal.h b/mm/internal.h
> index 5a2ddcf68e0b..9d2198114510 100644
> --- a/mm/internal.h
> +++ b/mm/internal.h
> @@ -662,6 +662,16 @@ void calculate_min_free_kbytes(void);
> int __meminit init_per_zone_wmark_min(void);
> void page_alloc_sysctl_init(void);
>
> +/*
> + * Sentinel for user_addr: indicates a non-user allocation.
> + * Cannot use 0 because address 0 is a valid userspace mapping.
> + * (unsigned long)-1 is safe because:
> + * 1. vm_end = addr + len <= TASK_SIZE, and vm_end is exclusive,
> + * so -1 is never inside any VMA.
> + * 2. It will only be compared to page-aligned addresses.
> + */
> +#define USER_ADDR_NONE ((unsigned long)-1)
> +
> /*
> * Structure for holding the mostly immutable allocation parameters passed
> * between functions involved in allocations, including the alloc_pages*
> @@ -693,6 +703,7 @@ struct alloc_context {
> */
> enum zone_type highest_zoneidx;
> bool spread_dirty_pages;
> + unsigned long user_addr;
> };
>
> /*
> @@ -916,13 +927,14 @@ static inline void init_compound_tail(struct page *tail,
> prep_compound_tail(tail, head, order);
> }
>
> -void post_alloc_hook(struct page *page, unsigned int order, gfp_t gfp_flags);
> +void post_alloc_hook(struct page *page, unsigned int order, gfp_t gfp_flags,
> + unsigned long user_addr);
> extern bool free_pages_prepare(struct page *page, unsigned int order);
>
> extern int user_min_free_kbytes;
>
> struct page *__alloc_frozen_pages_noprof(gfp_t, unsigned int order, int nid,
> - nodemask_t *);
> + nodemask_t *, unsigned long user_addr);
> #define __alloc_frozen_pages(...) \
> alloc_hooks(__alloc_frozen_pages_noprof(__VA_ARGS__))
> void free_frozen_pages(struct page *page, unsigned int order);
> @@ -930,10 +942,13 @@ void free_unref_folios(struct folio_batch *fbatch);
>
> #ifdef CONFIG_NUMA
> struct page *alloc_frozen_pages_noprof(gfp_t, unsigned int order);
> +struct folio *folio_alloc_mpol_user_noprof(gfp_t gfp, unsigned int order,
> + struct mempolicy *pol, pgoff_t ilx, int nid,
> + unsigned long user_addr);
> #else
> static inline struct page *alloc_frozen_pages_noprof(gfp_t gfp, unsigned int order)
> {
> - return __alloc_frozen_pages_noprof(gfp, order, numa_node_id(), NULL);
> + return __alloc_frozen_pages_noprof(gfp, order, numa_node_id(), NULL, USER_ADDR_NONE);
> }
> #endif
>
> diff --git a/mm/mempolicy.c b/mm/mempolicy.c
> index a1707ad498a8..f573ff32e94d 100644
> --- a/mm/mempolicy.c
> +++ b/mm/mempolicy.c
> @@ -2413,7 +2413,8 @@ bool mempolicy_in_oom_domain(struct task_struct *tsk,
> }
>
> static struct page *alloc_pages_preferred_many(gfp_t gfp, unsigned int order,
> - int nid, nodemask_t *nodemask)
> + int nid, nodemask_t *nodemask,
> + unsigned long user_addr)
> {
> struct page *page;
> gfp_t preferred_gfp;
> @@ -2426,25 +2427,29 @@ static struct page *alloc_pages_preferred_many(gfp_t gfp, unsigned int order,
> */
> preferred_gfp = gfp | __GFP_NOWARN;
> preferred_gfp &= ~(__GFP_DIRECT_RECLAIM | __GFP_NOFAIL);
> - page = __alloc_frozen_pages_noprof(preferred_gfp, order, nid, nodemask);
> + page = __alloc_frozen_pages_noprof(preferred_gfp, order, nid,
> + nodemask, user_addr);
> if (!page)
> - page = __alloc_frozen_pages_noprof(gfp, order, nid, NULL);
> + page = __alloc_frozen_pages_noprof(gfp, order, nid, NULL,
> + user_addr);
>
> return page;
> }
>
> /**
> - * alloc_pages_mpol - Allocate pages according to NUMA mempolicy.
> + * __alloc_pages_mpol - Allocate pages according to NUMA mempolicy.
> * @gfp: GFP flags.
> * @order: Order of the page allocation.
> * @pol: Pointer to the NUMA mempolicy.
> * @ilx: Index for interleave mempolicy (also distinguishes alloc_pages()).
> * @nid: Preferred node (usually numa_node_id() but @mpol may override it).
> + * @user_addr: User fault address for cache-friendly zeroing, or USER_ADDR_NONE.
OK this isn't great - 'for cache-friendly zeroing' is vague, confusing, and
an break in the abstraction (don't tell me one specific detail of what
you're doing down the callstack) .
'User fault address' is nebulous and confusing.
> *
> * Return: The page on success or NULL if allocation fails.
> */
> -static struct page *alloc_pages_mpol(gfp_t gfp, unsigned int order,
> - struct mempolicy *pol, pgoff_t ilx, int nid)
> +static struct page *__alloc_pages_mpol(gfp_t gfp, unsigned int order,
> + struct mempolicy *pol, pgoff_t ilx, int nid,
> + unsigned long user_addr)
> {
> nodemask_t *nodemask;
> struct page *page;
> @@ -2452,7 +2457,8 @@ static struct page *alloc_pages_mpol(gfp_t gfp, unsigned int order,
> nodemask = policy_nodemask(gfp, pol, ilx, &nid);
>
> if (pol->mode == MPOL_PREFERRED_MANY)
> - return alloc_pages_preferred_many(gfp, order, nid, nodemask);
> + return alloc_pages_preferred_many(gfp, order, nid, nodemask,
> + user_addr);
>
> if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE) &&
> /* filter "hugepage" allocation, unless from alloc_pages() */
> @@ -2476,7 +2482,7 @@ static struct page *alloc_pages_mpol(gfp_t gfp, unsigned int order,
> */
> page = __alloc_frozen_pages_noprof(
> gfp | __GFP_THISNODE | __GFP_NORETRY, order,
> - nid, NULL);
> + nid, NULL, user_addr);
> if (page || !(gfp & __GFP_DIRECT_RECLAIM))
> return page;
> /*
> @@ -2488,7 +2494,7 @@ static struct page *alloc_pages_mpol(gfp_t gfp, unsigned int order,
> }
> }
>
> - page = __alloc_frozen_pages_noprof(gfp, order, nid, nodemask);
> + page = __alloc_frozen_pages_noprof(gfp, order, nid, nodemask, user_addr);
>
> if (unlikely(pol->mode == MPOL_INTERLEAVE ||
> pol->mode == MPOL_WEIGHTED_INTERLEAVE) && page) {
> @@ -2504,11 +2510,18 @@ static struct page *alloc_pages_mpol(gfp_t gfp, unsigned int order,
> return page;
> }
>
> -struct folio *folio_alloc_mpol_noprof(gfp_t gfp, unsigned int order,
> +static struct page *alloc_pages_mpol(gfp_t gfp, unsigned int order,
> struct mempolicy *pol, pgoff_t ilx, int nid)
> {
> - struct page *page = alloc_pages_mpol(gfp | __GFP_COMP, order, pol,
> - ilx, nid);
> + return __alloc_pages_mpol(gfp, order, pol, ilx, nid, USER_ADDR_NONE);
> +}
> +
> +struct folio *folio_alloc_mpol_user_noprof(gfp_t gfp, unsigned int order,
> + struct mempolicy *pol, pgoff_t ilx, int nid,
> + unsigned long user_addr)
> +{
> + struct page *page = __alloc_pages_mpol(gfp | __GFP_COMP, order, pol,
> + ilx, nid, user_addr);
> if (!page)
> return NULL;
>
> @@ -2516,6 +2529,13 @@ struct folio *folio_alloc_mpol_noprof(gfp_t gfp, unsigned int order,
> return page_rmappable_folio(page);
> }
>
> +struct folio *folio_alloc_mpol_noprof(gfp_t gfp, unsigned int order,
> + struct mempolicy *pol, pgoff_t ilx, int nid)
> +{
> + return folio_alloc_mpol_user_noprof(gfp, order, pol, ilx, nid,
> + USER_ADDR_NONE);
> +}
> +
> struct page *alloc_frozen_pages_noprof(gfp_t gfp, unsigned order)
> {
> struct mempolicy *pol = &default_policy;
> diff --git a/mm/mmap.c b/mm/mmap.c
> index 5754d1c36462..73413cebc418 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -855,6 +855,12 @@ __get_unmapped_area(struct file *file, unsigned long addr, unsigned long len,
> if (IS_ERR_VALUE(addr))
> return addr;
>
> + /*
> + * The check below ensures vm_end = addr + len <= TASK_SIZE.
> + * Since (unsigned long)-1 (USER_ADDR_NONE) >= TASK_SIZE and
> + * vm_end is exclusive, USER_ADDR_NONE is thus never a valid
> + * userspace address.
> + */
You're adding what seems to be an AI-generated comment randomly here for some
reason? Let's not thanks?
> if (addr > TASK_SIZE - len)
> return -ENOMEM;
> if (offset_in_page(addr))
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 6a605d05e8cd..21b52c879751 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -1815,7 +1815,7 @@ static inline bool should_skip_init(gfp_t flags)
> }
>
> inline void post_alloc_hook(struct page *page, unsigned int order,
> - gfp_t gfp_flags)
> + gfp_t gfp_flags, unsigned long user_addr)
> {
> const bool zero_tags = gfp_flags & __GFP_ZEROTAGS;
> bool init = !want_init_on_free() && want_init_on_alloc(gfp_flags) &&
> @@ -1870,9 +1870,10 @@ inline void post_alloc_hook(struct page *page, unsigned int order,
> }
>
> static void prep_new_page(struct page *page, unsigned int order, gfp_t gfp_flags,
> - unsigned int alloc_flags)
> + unsigned int alloc_flags,
> + unsigned long user_addr)
> {
> - post_alloc_hook(page, order, gfp_flags);
> + post_alloc_hook(page, order, gfp_flags, user_addr);
>
> if (order && (gfp_flags & __GFP_COMP))
> prep_compound_page(page, order);
> @@ -3956,7 +3957,8 @@ get_page_from_freelist(gfp_t gfp_mask, unsigned int order, int alloc_flags,
> page = rmqueue(zonelist_zone(ac->preferred_zoneref), zone, order,
> gfp_mask, alloc_flags, ac->migratetype);
> if (page) {
> - prep_new_page(page, order, gfp_mask, alloc_flags);
> + prep_new_page(page, order, gfp_mask, alloc_flags,
> + ac->user_addr);
>
> return page;
> } else {
> @@ -4184,7 +4186,8 @@ __alloc_pages_direct_compact(gfp_t gfp_mask, unsigned int order,
>
> /* Prep a captured page if available */
> if (page)
> - prep_new_page(page, order, gfp_mask, alloc_flags);
> + prep_new_page(page, order, gfp_mask, alloc_flags,
> + ac->user_addr);
>
> /* Try get a page from the freelist if available */
> if (!page)
> @@ -5061,7 +5064,7 @@ unsigned long alloc_pages_bulk_noprof(gfp_t gfp, int preferred_nid,
> struct zoneref *z;
> struct per_cpu_pages *pcp;
> struct list_head *pcp_list;
> - struct alloc_context ac;
> + struct alloc_context ac = { .user_addr = USER_ADDR_NONE };
> gfp_t alloc_gfp;
> unsigned int alloc_flags = ALLOC_WMARK_LOW;
> int nr_populated = 0, nr_account = 0;
> @@ -5176,7 +5179,7 @@ unsigned long alloc_pages_bulk_noprof(gfp_t gfp, int preferred_nid,
> }
> nr_account++;
>
> - prep_new_page(page, 0, gfp, 0);
> + prep_new_page(page, 0, gfp, 0, USER_ADDR_NONE);
> set_page_refcounted(page);
> page_array[nr_populated++] = page;
> }
> @@ -5201,12 +5204,13 @@ EXPORT_SYMBOL_GPL(alloc_pages_bulk_noprof);
> * This is the 'heart' of the zoned buddy allocator.
> */
> struct page *__alloc_frozen_pages_noprof(gfp_t gfp, unsigned int order,
> - int preferred_nid, nodemask_t *nodemask)
> + int preferred_nid, nodemask_t *nodemask,
> + unsigned long user_addr)
> {
> struct page *page;
> unsigned int alloc_flags = ALLOC_WMARK_LOW;
> gfp_t alloc_gfp; /* The gfp_t that was actually used for allocation */
> - struct alloc_context ac = { };
> + struct alloc_context ac = { .user_addr = user_addr };
>
> /*
> * There are several places where we assume that the order value is sane
> @@ -5267,10 +5271,12 @@ EXPORT_SYMBOL(__alloc_frozen_pages_noprof);
>
> struct page *__alloc_pages_noprof(gfp_t gfp, unsigned int order,
> int preferred_nid, nodemask_t *nodemask)
> +
> {
> struct page *page;
>
> - page = __alloc_frozen_pages_noprof(gfp, order, preferred_nid, nodemask);
> + page = __alloc_frozen_pages_noprof(gfp, order, preferred_nid,
> + nodemask, USER_ADDR_NONE);
> if (page)
> set_page_refcounted(page);
> return page;
> @@ -5313,7 +5319,8 @@ struct folio *vma_alloc_folio_noprof(gfp_t gfp, int order,
> gfp |= __GFP_NOWARN;
>
> pol = get_vma_policy(vma, addr, order, &ilx);
> - folio = folio_alloc_mpol_noprof(gfp, order, pol, ilx, numa_node_id());
> + folio = folio_alloc_mpol_user_noprof(gfp, order, pol, ilx,
> + numa_node_id(), addr);
> mpol_cond_put(pol);
> return folio;
> }
> @@ -5321,10 +5328,17 @@ struct folio *vma_alloc_folio_noprof(gfp_t gfp, int order,
> struct folio *vma_alloc_folio_noprof(gfp_t gfp, int order,
> struct vm_area_struct *vma, unsigned long addr)
> {
> + struct page *page;
> +
> if (vma->vm_flags & VM_DROPPABLE)
> gfp |= __GFP_NOWARN;
>
> - return folio_alloc_noprof(gfp, order);
> + page = __alloc_frozen_pages_noprof(gfp | __GFP_COMP, order,
> + numa_node_id(), NULL, addr);
> + if (!page)
> + return NULL;
> + set_page_refcounted(page);
> + return page_rmappable_folio(page);
Err, what?
You're adding arbitrary new code here? What's the justification? Is it an
open-coded version of what was there before just to propagate the addr?
In any case this is totally unacceptable, don't open code like this, don't
make changes like this when the commit message doesn't mention them.
> }
> #endif
> EXPORT_SYMBOL(vma_alloc_folio_noprof);
> @@ -6905,7 +6919,7 @@ static void split_free_frozen_pages(struct list_head *list, gfp_t gfp_mask)
> list_for_each_entry_safe(page, next, &list[order], lru) {
> int i;
>
> - post_alloc_hook(page, order, gfp_mask);
> + post_alloc_hook(page, order, gfp_mask, USER_ADDR_NONE);
> if (!order)
> continue;
>
> @@ -7111,7 +7125,7 @@ int alloc_contig_frozen_range_noprof(unsigned long start, unsigned long end,
> struct page *head = pfn_to_page(start);
>
> check_new_pages(head, order);
> - prep_new_page(head, order, gfp_mask, 0);
> + prep_new_page(head, order, gfp_mask, 0, USER_ADDR_NONE);
> } else {
> ret = -EINVAL;
> WARN(true, "PFN range: requested [%lu, %lu), allocated [%lu, %lu)\n",
> @@ -7776,7 +7790,7 @@ struct page *alloc_frozen_pages_nolock_noprof(gfp_t gfp_flags, int nid, unsigned
> gfp_t alloc_gfp = __GFP_NOWARN | __GFP_ZERO | __GFP_NOMEMALLOC | __GFP_COMP
> | gfp_flags;
> unsigned int alloc_flags = ALLOC_TRYLOCK;
> - struct alloc_context ac = { };
> + struct alloc_context ac = { .user_addr = USER_ADDR_NONE };
> struct page *page;
>
> VM_WARN_ON_ONCE(gfp_flags & ~__GFP_ACCOUNT);
> diff --git a/mm/slub.c b/mm/slub.c
> index a2bf3756ca7d..f397fa2f3f80 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -3275,7 +3275,7 @@ static inline struct slab *alloc_slab_page(gfp_t flags, int node,
> else if (node == NUMA_NO_NODE)
> page = alloc_frozen_pages(flags, order);
> else
> - page = __alloc_frozen_pages(flags, order, node, NULL);
> + page = __alloc_frozen_pages(flags, order, node, NULL, USER_ADDR_NONE);
>
> if (!page)
> return NULL;
> @@ -5236,7 +5236,7 @@ static void *___kmalloc_large_node(size_t size, gfp_t flags, int node)
> if (node == NUMA_NO_NODE)
> page = alloc_frozen_pages_noprof(flags, order);
> else
> - page = __alloc_frozen_pages_noprof(flags, order, node, NULL);
> + page = __alloc_frozen_pages_noprof(flags, order, node, NULL, USER_ADDR_NONE);
>
> if (page) {
> ptr = page_address(page);
> --
> MST
>
Thanks, Lorenzo
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