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608c745597
Patch series "mm: preparatory patches for PMD level swap entries", v2.
This is the preparatory part of the PMD page table swapin work. The full
PMD swap entry series has been split into two parts:
1. this preparatory series, which contains the first 6 patches. Zi [1]
and Lance [2] suggested to separate this out from the core series.
2. the PMD swap entry core series, which depends on this one. I will
send this once the preparatory series is merged in mm-new as v3
as the combined is currently at v2 [1].
I have not marked this prep series as v3, as its not really adding
support for PMD swap entries.
This series does not introduce PMD swap entries and does not install any
new page-table entry type. It only cleans up existing PMD softleaf
helpers and call sites so the follow-up PMD swap entry series can be
smaller and easier to review.
It should be safe to merge independently. The patches are either helper
additions, refactors of existing open-coded logic, defensive checks that
preserve current migration/device-private behavior, or a mechanical rename
of the PMD softleaf Kconfig gate. The follow-up series depends on these
helpers, but this series does not depend on the follow-up series.
Patch breakdown:
1. mm: add softleaf_to_pmd() and convert existing callers
Add the PMD counterpart to softleaf_to_pte() and convert existing
swp_entry_to_pmd() users that are constructing PMD softleaf
entries.
2. mm: extract mm_prepare_for_swap_entries() helper
Hoist the "register mm with swapoff" double-checked-locking
pattern out of try_to_unmap_one() and copy_nonpresent_pte() so
future PMD-level users do not need another open-coded copy.
3. fs/proc: use softleaf_has_pfn() in pagemap PMD walker
Avoid assuming every non-present PMD softleaf entry encodes a PFN.
Existing migration/device-private behavior is preserved.
4. mm/huge_memory: move softleaf_to_folio() inside migration branch
Keep the folio lookup in change_non_present_huge_pmd() scoped to
the migration-entry branch that actually needs it.
5. mm/migrate_device: move softleaf_to_folio() inside device-private
branch
Apply the same ordering cleanup to migrate_vma_collect_pmd(): only
derive a folio after confirming the PMD entry is device-private.
6. mm: rename ARCH_ENABLE_THP_MIGRATION to ARCH_HAS_PMD_SOFTLEAVES
Rename the architecture gate to describe what it actually enables:
PMD softleaf entries. Migration remains the only current user in
this series; the follow-up series adds PMD swap entries.
This patch (of 6):
Add softleaf_to_pmd() as the PMD counterpart to softleaf_to_pte(),
completing the symmetry of the softleaf abstraction for page table leaf
entries.
The upcoming PMD swap entry support needs to construct PMD entries from
swap entries. Converting existing swp_entry_to_pmd() callers to
softleaf_to_pmd() in a prep patch keeps the feature patches focused on new
functionality rather than mixing refactoring with new code.
Link: https://lore.kernel.org/20260706114320.1643046-1-usama.arif@linux.dev
Link: https://lore.kernel.org/20260706114320.1643046-2-usama.arif@linux.dev
Link: https://lore.kernel.org/all/6E99CC4E-A026-4DE3-8A5A-34216771F521@nvidia.com/ [1]
Link: https://lore.kernel.org/all/b08cafbb-a4b7-4609-84ae-dbb2cfcfc8be@linux.dev/#t [2]
Link: https://lore.kernel.org/all/20260602142537.198755-1-usama.arif@linux.dev/ [3]
Signed-off-by: Usama Arif <usama.arif@linux.dev>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Reviewed-by: Lance Yang <lance.yang@linux.dev>
Cc: Alexandre Ghiti <alex@ghiti.fr>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Baoquan He <baoquan.he@linux.dev>
Cc: Barry Song <baohua@kernel.org>
Cc: Chris Li <chrisl@kernel.org>
Cc: Dev Jain <dev.jain@arm.com>
Cc: "Huang, Ying" <ying.huang@linux.alibaba.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Kairui Song <kasong@tencent.com>
Cc: Kemeng Shi <shikemeng@huaweicloud.com>
Cc: Kiryl Shutsemau <kas@kernel.org>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Nhat Pham <nphamcs@gmail.com>
Cc: Nico Pache <npache@redhat.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Vlastimil Babka <vbabka@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
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