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Message-ID: <1b896491-d9c0-4c8d-bc60-47579c773dce@nvidia.com>
Date: Tue, 23 Sep 2025 13:39:07 +1000
From: Balbir Singh <balbirs@...dia.com>
To: Zi Yan <ziy@...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 9/23/25 06:13, Zi Yan wrote:
> 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).
I'll protect it accordingly, thanks!
>
>> } 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 ...
>
>
Sure, can do and repeat the comment or just say look at the comments for !pte_present() :)
>> + 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.
>
I can't find any examples of mixing declarations and could not find any clear
guidance in the coding style
>> 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>
Thanks for the review,
Balbir
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