[PATCH 0/3] mm: fixes for THP migration, swap-in and device-private smaps

[Usama Arif <usama.arif@linux.dev>]

This series contains three fixes for existing THP migration, PTE swap-in
and smaps paths. They were extracted from the work on PMD swap entries
for anonymous THPs [1] and can be merged independently. Sending this
separately as requested by Andrew (should have sent them separately
anyways, my bad).

1. Avoid a folio reference leak when concurrent MADV_DONTNEED clears
   or splits a migration PMD before the device migration split helper
   acquires the PMD lock.

2. Prevent PTE swap-in batching from mapping poisoned subpages of a
   large swap-cache folio. Include the subpage scan helper with this
   fix so it can be applied on its own.

3. Account device-private PMDs using mapcounts in smaps, matching the
   PTE path. Shared mappings get proportional PSS, and exclusive
   mappings are counted as private.

[1] PMD-level swap entries for anonymous THPs:
https://lore.kernel.org/r/20261002095503.3585565-1-usama.arif@linux.dev/

Usama Arif (3):
  mm: don't PTE-batch a swap-in over a hardware-poisoned subpage
  fs/proc/task_mmu: don't read young/dirty from a non-present PMD in
    smaps
  fs/proc/task_mmu: account device-private PMDs as present in smaps

 fs/proc/task_mmu.c | 12 ++++++++----
 mm/internal.h      | 15 +++++++++++++++
 mm/memory.c        |  4 ++++
 3 files changed, 27 insertions(+), 4 deletions(-)

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