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Message-ID: <c2d563b2-da9e-4e3b-989a-97f7eb828d6a@nvidia.com>
Date: Fri, 12 Sep 2025 14:51:53 +1000
From: Balbir Singh <balbirs@...dia.com>
To: SeongJae Park <sj@...nel.org>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org,
dri-devel@...ts.freedesktop.org, Andrew Morton <akpm@...ux-foundation.org>,
David Hildenbrand <david@...hat.com>, Zi Yan <ziy@...dia.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: [v5 03/15] mm/rmap: extend rmap and migration support
device-private entries
On 9/12/25 11:59, SeongJae Park wrote:
> On Mon, 8 Sep 2025 10:04:36 +1000 Balbir Singh <balbirs@...dia.com> 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.
>>
>> Cc: Andrew Morton <akpm@...ux-foundation.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>
>>
>> Signed-off-by: Balbir Singh <balbirs@...dia.com>
>> ---
>> mm/damon/ops-common.c | 20 +++++++++++++++++---
>> mm/huge_memory.c | 16 +++++++++++++++-
>> mm/page_idle.c | 5 +++--
>> mm/page_vma_mapped.c | 12 ++++++++++--
>> mm/rmap.c | 19 ++++++++++++++++---
>> 5 files changed, 61 insertions(+), 11 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);
>> + 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);
>
> Could you please elaborate more about why the above change is needed on the
> commit message?
>
> For example, I found below from v3 of this patch series:
>
> 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.
>
> Adding that kind of elaboration on the commit message would be helpful.
>
> Also, seems the DAMON part change is not really required to be made together
> with other changes. If I'm not wrong, could you make DAMON part change as a
> separate commit?
>
> The code looks good to me.
>
> Reviewed-by: SeongJae Park <sj@...nel.org>
>
>
Thanks SJ!
v3 had a separate flag during page vma mapped walk, so the walkers had to opt-in
with a flag, I removed that after David's review feedback
This change is required because we now support large folios in device private
and hence the DAMON changes are included in this patch
Balbir
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