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Message-ID: <f625e98a-ae1e-4327-8646-a8e5913000d2@redhat.com>
Date: Tue, 8 Jul 2025 07:30:06 +0300
From: Mika Penttilä <mpenttil@...hat.com>
To: Balbir Singh <balbirs@...dia.com>, linux-mm@...ck.org
Cc: akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
Karol Herbst <kherbst@...hat.com>, Lyude Paul <lyude@...hat.com>,
Danilo Krummrich <dakr@...nel.org>, David Airlie <airlied@...il.com>,
Simona Vetter <simona@...ll.ch>, Jérôme Glisse
<jglisse@...hat.com>, Shuah Khan <shuah@...nel.org>,
David Hildenbrand <david@...hat.com>, Barry Song <baohua@...nel.org>,
Baolin Wang <baolin.wang@...ux.alibaba.com>,
Ryan Roberts <ryan.roberts@....com>, Matthew Wilcox <willy@...radead.org>,
Peter Xu <peterx@...hat.com>, Zi Yan <ziy@...dia.com>,
Kefeng Wang <wangkefeng.wang@...wei.com>, Jane Chu <jane.chu@...cle.com>,
Alistair Popple <apopple@...dia.com>, Donet Tom <donettom@...ux.ibm.com>
Subject: Re: [v1 resend 03/12] mm/thp: zone_device awareness in THP handling
code
On 7/8/25 07:20, Balbir Singh wrote:
> On 7/7/25 13:49, Mika Penttilä wrote:
>> On 7/4/25 02:35, Balbir Singh wrote:
>>> Make THP handling code in the mm subsystem for THP pages
>>> aware of zone device pages. Although the code is
>>> designed to be generic when it comes to handling splitting
>>> of pages, the code is designed to work for THP page sizes
>>> corresponding to HPAGE_PMD_NR.
>>>
>>> Modify page_vma_mapped_walk() to return true when a zone
>>> device huge entry is present, enabling try_to_migrate()
>>> and other code migration paths to appropriately process the
>>> entry
>>>
>>> pmd_pfn() does not work well with zone device entries, use
>>> pfn_pmd_entry_to_swap() for checking and comparison as for
>>> zone device entries.
>>>
>>> try_to_map_to_unused_zeropage() does not apply to zone device
>>> entries, zone device entries are ignored in the call.
>>>
>>> Cc: Karol Herbst <kherbst@...hat.com>
>>> 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: "Jérôme Glisse" <jglisse@...hat.com>
>>> Cc: Shuah Khan <shuah@...nel.org>
>>> Cc: David Hildenbrand <david@...hat.com>
>>> Cc: Barry Song <baohua@...nel.org>
>>> Cc: Baolin Wang <baolin.wang@...ux.alibaba.com>
>>> Cc: Ryan Roberts <ryan.roberts@....com>
>>> Cc: Matthew Wilcox <willy@...radead.org>
>>> Cc: Peter Xu <peterx@...hat.com>
>>> Cc: Zi Yan <ziy@...dia.com>
>>> Cc: Kefeng Wang <wangkefeng.wang@...wei.com>
>>> Cc: Jane Chu <jane.chu@...cle.com>
>>> Cc: Alistair Popple <apopple@...dia.com>
>>> Cc: Donet Tom <donettom@...ux.ibm.com>
>>>
>>> Signed-off-by: Balbir Singh <balbirs@...dia.com>
>>> ---
>>> mm/huge_memory.c | 153 +++++++++++++++++++++++++++++++------------
>>> mm/migrate.c | 2 +
>>> mm/page_vma_mapped.c | 10 +++
>>> mm/pgtable-generic.c | 6 ++
>>> mm/rmap.c | 19 +++++-
>>> 5 files changed, 146 insertions(+), 44 deletions(-)
>>>
>>> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
>>> index ce130225a8e5..e6e390d0308f 100644
>>> --- a/mm/huge_memory.c
>>> +++ b/mm/huge_memory.c
>>> @@ -1711,7 +1711,8 @@ int copy_huge_pmd(struct mm_struct *dst_mm, struct mm_struct *src_mm,
>>> if (unlikely(is_swap_pmd(pmd))) {
>>> swp_entry_t entry = pmd_to_swp_entry(pmd);
>>>
>>> - VM_BUG_ON(!is_pmd_migration_entry(pmd));
>>> + VM_BUG_ON(!is_pmd_migration_entry(pmd) &&
>>> + !is_device_private_entry(entry));
>>> if (!is_readable_migration_entry(entry)) {
>>> entry = make_readable_migration_entry(
>>> swp_offset(entry));
>>> @@ -2222,10 +2223,17 @@ int zap_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
>>> } else if (thp_migration_supported()) {
>>> swp_entry_t entry;
>>>
>>> - VM_BUG_ON(!is_pmd_migration_entry(orig_pmd));
>>> entry = pmd_to_swp_entry(orig_pmd);
>>> folio = pfn_swap_entry_folio(entry);
>>> flush_needed = 0;
>>> +
>>> + VM_BUG_ON(!is_pmd_migration_entry(*pmd) &&
>>> + !folio_is_device_private(folio));
>>> +
>>> + if (folio_is_device_private(folio)) {
>>> + folio_remove_rmap_pmd(folio, folio_page(folio, 0), vma);
>>> + WARN_ON_ONCE(folio_mapcount(folio) < 0);
>>> + }
>>> } else
>>> WARN_ONCE(1, "Non present huge pmd without pmd migration enabled!");
>>>
>>> @@ -2247,6 +2255,15 @@ int zap_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
>>> folio_mark_accessed(folio);
>>> }
>>>
>>> + /*
>>> + * Do a folio put on zone device private pages after
>>> + * changes to mm_counter, because the folio_put() will
>>> + * clean folio->mapping and the folio_test_anon() check
>>> + * will not be usable.
>>> + */
>>> + if (folio_is_device_private(folio))
>>> + folio_put(folio);
>>> +
>>> spin_unlock(ptl);
>>> if (flush_needed)
>>> tlb_remove_page_size(tlb, &folio->page, HPAGE_PMD_SIZE);
>>> @@ -2375,7 +2392,8 @@ int change_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
>>> struct folio *folio = pfn_swap_entry_folio(entry);
>>> pmd_t newpmd;
>>>
>>> - VM_BUG_ON(!is_pmd_migration_entry(*pmd));
>>> + VM_BUG_ON(!is_pmd_migration_entry(*pmd) &&
>>> + !folio_is_device_private(folio));
>>> if (is_writable_migration_entry(entry)) {
>>> /*
>>> * A protection check is difficult so
>>> @@ -2388,9 +2406,11 @@ int change_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
>>> newpmd = swp_entry_to_pmd(entry);
>>> if (pmd_swp_soft_dirty(*pmd))
>>> newpmd = pmd_swp_mksoft_dirty(newpmd);
>>> - } else {
>>> + } else if (is_writable_device_private_entry(entry)) {
>>> + newpmd = swp_entry_to_pmd(entry);
>>> + entry = make_device_exclusive_entry(swp_offset(entry));
>>> + } else
>>> newpmd = *pmd;
>>> - }
>>>
>>> if (uffd_wp)
>>> newpmd = pmd_swp_mkuffd_wp(newpmd);
>>> @@ -2842,16 +2862,20 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
>>> struct page *page;
>>> pgtable_t pgtable;
>>> pmd_t old_pmd, _pmd;
>>> - bool young, write, soft_dirty, pmd_migration = false, uffd_wp = false;
>>> - bool anon_exclusive = false, dirty = false;
>>> + bool young, write, soft_dirty, uffd_wp = false;
>>> + bool anon_exclusive = false, dirty = false, present = false;
>>> unsigned long addr;
>>> pte_t *pte;
>>> int i;
>>> + swp_entry_t swp_entry;
>>>
>>> VM_BUG_ON(haddr & ~HPAGE_PMD_MASK);
>>> VM_BUG_ON_VMA(vma->vm_start > haddr, vma);
>>> VM_BUG_ON_VMA(vma->vm_end < haddr + HPAGE_PMD_SIZE, vma);
>>> - VM_BUG_ON(!is_pmd_migration_entry(*pmd) && !pmd_trans_huge(*pmd));
>>> +
>>> + VM_BUG_ON(!is_pmd_migration_entry(*pmd) && !pmd_trans_huge(*pmd)
>>> + && !(is_swap_pmd(*pmd) &&
>>> + is_device_private_entry(pmd_to_swp_entry(*pmd))));
>>>
>>> count_vm_event(THP_SPLIT_PMD);
>>>
>>> @@ -2899,20 +2923,25 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
>>> return __split_huge_zero_page_pmd(vma, haddr, pmd);
>>> }
>>>
>>> - pmd_migration = is_pmd_migration_entry(*pmd);
>>> - if (unlikely(pmd_migration)) {
>>> - swp_entry_t entry;
>>>
>>> + present = pmd_present(*pmd);
>>> + if (unlikely(!present)) {
>>> + swp_entry = pmd_to_swp_entry(*pmd);
>>> old_pmd = *pmd;
>>> - entry = pmd_to_swp_entry(old_pmd);
>>> - page = pfn_swap_entry_to_page(entry);
>>> - write = is_writable_migration_entry(entry);
>>> +
>>> + folio = pfn_swap_entry_folio(swp_entry);
>>> + VM_BUG_ON(!is_migration_entry(swp_entry) &&
>>> + !is_device_private_entry(swp_entry));
>>> + page = pfn_swap_entry_to_page(swp_entry);
>>> + write = is_writable_migration_entry(swp_entry);
>>> +
>>> if (PageAnon(page))
>>> - anon_exclusive = is_readable_exclusive_migration_entry(entry);
>>> - young = is_migration_entry_young(entry);
>>> - dirty = is_migration_entry_dirty(entry);
>>> + anon_exclusive =
>>> + is_readable_exclusive_migration_entry(swp_entry);
>>> soft_dirty = pmd_swp_soft_dirty(old_pmd);
>>> uffd_wp = pmd_swp_uffd_wp(old_pmd);
>>> + young = is_migration_entry_young(swp_entry);
>>> + dirty = is_migration_entry_dirty(swp_entry);
>>> } else {
>> This is where folio_try_share_anon_rmap_pmd() is skipped for device private pages, to which I referred in
>> https://lore.kernel.org/linux-mm/f1e26e18-83db-4c0e-b8d8-0af8ffa8a206@redhat.com/
>>
> Does it matter for device private pages/folios? It does not affect the freeze value.
I think ClearPageAnonExclusive is needed.
>
> Balbir Singh
>
--Mika
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