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Message-ID: <D4440A30-118E-40DF-99BD-6F58B708E597@nvidia.com>
Date: Mon, 22 Sep 2025 16:13:47 -0400
From: Zi Yan <ziy@...dia.com>
To: Balbir Singh <balbirs@...dia.com>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org, damon@...ts.linux.dev,
dri-devel@...ts.freedesktop.org, SeongJae Park <sj@...nel.org>,
David Hildenbrand <david@...hat.com>, Joshua Hahn <joshua.hahnjy@...il.com>,
Rakie Kim <rakie.kim@...com>, Byungchul Park <byungchul@...com>,
Gregory Price <gourry@...rry.net>, Ying Huang <ying.huang@...ux.alibaba.com>,
Alistair Popple <apopple@...dia.com>, Oscar Salvador <osalvador@...e.de>,
Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
Baolin Wang <baolin.wang@...ux.alibaba.com>,
"Liam R. Howlett" <Liam.Howlett@...cle.com>, Nico Pache <npache@...hat.com>,
Ryan Roberts <ryan.roberts@....com>, Dev Jain <dev.jain@....com>,
Barry Song <baohua@...nel.org>, Lyude Paul <lyude@...hat.com>,
Danilo Krummrich <dakr@...nel.org>, David Airlie <airlied@...il.com>,
Simona Vetter <simona@...ll.ch>, Ralph Campbell <rcampbell@...dia.com>,
Mika Penttilä <mpenttil@...hat.com>,
Matthew Brost <matthew.brost@...el.com>,
Francois Dugast <francois.dugast@...el.com>
Subject: Re: [v6 03/15] mm/rmap: extend rmap and migration support
device-private entries
On 16 Sep 2025, at 8:21, Balbir Singh wrote:
> Add device-private THP support to reverse mapping infrastructure, enabling
> proper handling during migration and walk operations.
>
> The key changes are:
> - add_migration_pmd()/remove_migration_pmd(): Handle device-private
> entries during folio migration and splitting
> - page_vma_mapped_walk(): Recognize device-private THP entries during
> VMA traversal operations
>
> This change supports folio splitting and migration operations on
> device-private entries.
>
> Signed-off-by: Balbir Singh <balbirs@...dia.com>
> Reviewed-by: SeongJae Park <sj@...nel.org>
> Cc: David Hildenbrand <david@...hat.com>
> Cc: Zi Yan <ziy@...dia.com>
> Cc: Joshua Hahn <joshua.hahnjy@...il.com>
> Cc: Rakie Kim <rakie.kim@...com>
> Cc: Byungchul Park <byungchul@...com>
> Cc: Gregory Price <gourry@...rry.net>
> Cc: Ying Huang <ying.huang@...ux.alibaba.com>
> Cc: Alistair Popple <apopple@...dia.com>
> Cc: Oscar Salvador <osalvador@...e.de>
> Cc: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
> Cc: Baolin Wang <baolin.wang@...ux.alibaba.com>
> Cc: "Liam R. Howlett" <Liam.Howlett@...cle.com>
> Cc: Nico Pache <npache@...hat.com>
> Cc: Ryan Roberts <ryan.roberts@....com>
> Cc: Dev Jain <dev.jain@....com>
> Cc: Barry Song <baohua@...nel.org>
> Cc: Lyude Paul <lyude@...hat.com>
> Cc: Danilo Krummrich <dakr@...nel.org>
> Cc: David Airlie <airlied@...il.com>
> Cc: Simona Vetter <simona@...ll.ch>
> Cc: Ralph Campbell <rcampbell@...dia.com>
> Cc: Mika Penttilä <mpenttil@...hat.com>
> Cc: Matthew Brost <matthew.brost@...el.com>
> Cc: Francois Dugast <francois.dugast@...el.com>
> ---
> mm/damon/ops-common.c | 20 +++++++++++++++++---
> mm/huge_memory.c | 16 +++++++++++++++-
> mm/page_idle.c | 7 +++++--
> mm/page_vma_mapped.c | 7 +++++++
> mm/rmap.c | 21 +++++++++++++++++----
> 5 files changed, 61 insertions(+), 10 deletions(-)
>
> diff --git a/mm/damon/ops-common.c b/mm/damon/ops-common.c
> index 998c5180a603..eda4de553611 100644
> --- a/mm/damon/ops-common.c
> +++ b/mm/damon/ops-common.c
> @@ -75,12 +75,24 @@ void damon_ptep_mkold(pte_t *pte, struct vm_area_struct *vma, unsigned long addr
> void damon_pmdp_mkold(pmd_t *pmd, struct vm_area_struct *vma, unsigned long addr)
> {
> #ifdef CONFIG_TRANSPARENT_HUGEPAGE
> - struct folio *folio = damon_get_folio(pmd_pfn(pmdp_get(pmd)));
> + pmd_t pmdval = pmdp_get(pmd);
> + struct folio *folio;
> + bool young = false;
> + unsigned long pfn;
> +
> + if (likely(pmd_present(pmdval)))
> + pfn = pmd_pfn(pmdval);
> + else
> + pfn = swp_offset_pfn(pmd_to_swp_entry(pmdval));
>
> + folio = damon_get_folio(pfn);
> if (!folio)
> return;
>
> - if (pmdp_clear_young_notify(vma, addr, pmd))
> + if (likely(pmd_present(pmdval)))
> + young |= pmdp_clear_young_notify(vma, addr, pmd);
> + young |= mmu_notifier_clear_young(vma->vm_mm, addr, addr + PAGE_SIZE);
This should be HPAGE_PMD_SIZE (it is guarded in CONFIG_TRANSPARENT_HUGEPAGE,
so HPAGE_PMD_SIZE will not trigger a build bug like the one below).
> + if (young)
> folio_set_young(folio);
>
> folio_set_idle(folio);
> @@ -203,7 +215,9 @@ static bool damon_folio_young_one(struct folio *folio,
> mmu_notifier_test_young(vma->vm_mm, addr);
> } else {
> #ifdef CONFIG_TRANSPARENT_HUGEPAGE
> - *accessed = pmd_young(pmdp_get(pvmw.pmd)) ||
> + pmd_t pmd = pmdp_get(pvmw.pmd);
> +
> + *accessed = (pmd_present(pmd) && pmd_young(pmd)) ||
> !folio_test_idle(folio) ||
> mmu_notifier_test_young(vma->vm_mm, addr);
> #else
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index a5e4c2aef191..78166db72f4d 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -4637,7 +4637,10 @@ int set_pmd_migration_entry(struct page_vma_mapped_walk *pvmw,
> return 0;
>
> flush_cache_range(vma, address, address + HPAGE_PMD_SIZE);
> - pmdval = pmdp_invalidate(vma, address, pvmw->pmd);
> + if (unlikely(!pmd_present(*pvmw->pmd)))
> + pmdval = pmdp_huge_get_and_clear(vma->vm_mm, address, pvmw->pmd);
> + else
> + pmdval = pmdp_invalidate(vma, address, pvmw->pmd);
>
> /* See folio_try_share_anon_rmap_pmd(): invalidate PMD first. */
> anon_exclusive = folio_test_anon(folio) && PageAnonExclusive(page);
> @@ -4687,6 +4690,17 @@ void remove_migration_pmd(struct page_vma_mapped_walk *pvmw, struct page *new)
> entry = pmd_to_swp_entry(*pvmw->pmd);
> folio_get(folio);
> pmde = folio_mk_pmd(folio, READ_ONCE(vma->vm_page_prot));
> +
> + if (folio_is_device_private(folio)) {
> + if (pmd_write(pmde))
> + entry = make_writable_device_private_entry(
> + page_to_pfn(new));
> + else
> + entry = make_readable_device_private_entry(
> + page_to_pfn(new));
> + pmde = swp_entry_to_pmd(entry);
> + }
> +
> if (pmd_swp_soft_dirty(*pvmw->pmd))
> pmde = pmd_mksoft_dirty(pmde);
> if (is_writable_migration_entry(entry))
> diff --git a/mm/page_idle.c b/mm/page_idle.c
> index a82b340dc204..3bf0fbe05cc2 100644
> --- a/mm/page_idle.c
> +++ b/mm/page_idle.c
> @@ -71,8 +71,11 @@ static bool page_idle_clear_pte_refs_one(struct folio *folio,
> referenced |= ptep_test_and_clear_young(vma, addr, pvmw.pte);
> referenced |= mmu_notifier_clear_young(vma->vm_mm, addr, addr + PAGE_SIZE);
> } else if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE)) {
> - if (pmdp_clear_young_notify(vma, addr, pvmw.pmd))
> - referenced = true;
> + pmd_t pmdval = pmdp_get(pvmw.pmd);
> +
> + if (likely(pmd_present(pmdval)))
> + referenced |= pmdp_clear_young_notify(vma, addr, pvmw.pmd);
> + referenced |= mmu_notifier_clear_young(vma->vm_mm, addr, addr + PAGE_SIZE);
This should be HPAGE_PMD_SIZE (or PMD_SIZE, since the code is not compiled
out when CONFIG_TRANSPARENT_HUGEPAGE is not selected and HPAGE_PMD_SIZE
will cause a build bug when CONFIG_PGTABLE_HAS_HUGE_LEAVES is not selected).
> } else {
> /* unexpected pmd-mapped page? */
> WARN_ON_ONCE(1);
> diff --git a/mm/page_vma_mapped.c b/mm/page_vma_mapped.c
> index e981a1a292d2..159953c590cc 100644
> --- a/mm/page_vma_mapped.c
> +++ b/mm/page_vma_mapped.c
> @@ -277,6 +277,13 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw)
> * cannot return prematurely, while zap_huge_pmd() has
> * cleared *pmd but not decremented compound_mapcount().
> */
> + swp_entry_t entry = pmd_to_swp_entry(pmde);
> +
> + if (is_device_private_entry(entry)) {
> + pvmw->ptl = pmd_lock(mm, pvmw->pmd);
> + return true;
> + }
> +
> if ((pvmw->flags & PVMW_SYNC) &&
> thp_vma_suitable_order(vma, pvmw->address,
> PMD_ORDER) &&
> diff --git a/mm/rmap.c b/mm/rmap.c
> index 9a2aabfaea6f..080fc4048431 100644
> --- a/mm/rmap.c
> +++ b/mm/rmap.c
> @@ -1063,9 +1063,11 @@ static int page_vma_mkclean_one(struct page_vma_mapped_walk *pvmw)
> } else {
> #ifdef CONFIG_TRANSPARENT_HUGEPAGE
> pmd_t *pmd = pvmw->pmd;
> - pmd_t entry;
> + pmd_t entry = pmdp_get(pmd);
>
> - if (!pmd_dirty(*pmd) && !pmd_write(*pmd))
It is better to add a similar comment as the one above !pte_present().
Something like:
PFN swap PMDs, such as ...
> + if (!pmd_present(entry))
> + continue;
> + if (!pmd_dirty(entry) && !pmd_write(entry))
> continue;
>
> flush_cache_range(vma, address,
> @@ -2330,6 +2332,11 @@ static bool try_to_migrate_one(struct folio *folio, struct vm_area_struct *vma,
> while (page_vma_mapped_walk(&pvmw)) {
> /* PMD-mapped THP migration entry */
> if (!pvmw.pte) {
> +#ifdef CONFIG_ARCH_ENABLE_THP_MIGRATION
> + unsigned long pfn;
> + pmd_t pmdval;
> +#endif
> +
This looks ugly. IIRC, we now can put variable definition in the middle.
Maybe for this case, these two can be moved to the below ifdef region.
> if (flags & TTU_SPLIT_HUGE_PMD) {
> split_huge_pmd_locked(vma, pvmw.address,
> pvmw.pmd, true);
> @@ -2338,8 +2345,14 @@ static bool try_to_migrate_one(struct folio *folio, struct vm_area_struct *vma,
> break;
> }
> #ifdef CONFIG_ARCH_ENABLE_THP_MIGRATION
> - subpage = folio_page(folio,
> - pmd_pfn(*pvmw.pmd) - folio_pfn(folio));
> + pmdval = pmdp_get(pvmw.pmd);
> + if (likely(pmd_present(pmdval)))
> + pfn = pmd_pfn(pmdval);
> + else
> + pfn = swp_offset_pfn(pmd_to_swp_entry(pmdval));
> +
> + subpage = folio_page(folio, pfn - folio_pfn(folio));
> +
> VM_BUG_ON_FOLIO(folio_test_hugetlb(folio) ||
> !folio_test_pmd_mappable(folio), folio);
>
> --
> 2.50.1
Otherwise, LGTM. Acked-by: Zi Yan <ziy@...dia.com>
Best Regards,
Yan, Zi
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