mm/rmap: Refactor try_to_unmap_one

In preparation for batching anonymous large folio unmapping to optimize it, refactor try_to_unmap_one. This series refactors hugetlb, anon-lazyfree and anon-swapbacked logic into their own functions, significantly reducing the length of the huge try_to_unmap_one.

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Based on mm-unstable (d8c677ce1220b0db119ada6c6f9762c07c4d8aca).

Split out from
https://lore.kernel.org/all/[email protected]/

mm-selftests pass on arm64, built on arm64 and x86.

v3->v4:
- Tighten comment around TTU_HWPOISON
- try_to_unmap_hugetlb_one -> try_to_unmap_poisoned_hugetlb_one
- VM_WARN_ON -> VM_WARN_ON_ONCE

v2->v3:
- Patch 2: fix comment to say that TTU_HWPOISON can be true for small folios only in try_to_unmap_one, since hugetlb bits are now refactored away
- Patch 5: Directly do if (WARN_ON_ONCE())
- Rebase on latest mm-unstable to resolve conflicts with 30c83145c5b3 ("mm: rename uffd-wp PTE accessors to uffd")

v1->v2:
- constify ttu flags in try_to_unmap_hugetlb_one, move const variables up
- Assert address passed to try_to_unmap_hugetlb_one equals pvmw.address
- Patch 3: code and comment polishing, do the stat update in the function
- Remove unnecessary inline hints, remove set_swp_pte_at, instead have swp_pte_prepare + set_ptes. Rename subpage -> page. constify anon_exclusive.
- Do pte restoration in caller

Dev Jain (5):
mm/rmap: convert page -> folio for hwpoison checks mm/rmap: Add try_to_unmap_poisoned_hugetlb_one mm/rmap: refactor some code around lazyfree folio unmapping mm/rmap: refactor anon folio unmap in try_to_unmap_one mm/rmap: add anon folio unmap dispatcher

 include/linux/hugetlb.h |   1 +
 mm/rmap.c               | 415 ++++++++++++++++++++++------------------
 2 files changed, 232 insertions(+), 184 deletions(-)

2.43.0