mm: consolidate anonymous folio PTE mapping into helpers

Patch series "mm: khugepaged cleanups and mTHP prerequisites", v4.

The following series contains cleanups and prerequisites for my work on
khugepaged mTHP support [1]. These have been separated out to ease
review.

The first patch in the series refactors the page fault folio to pte
mapping and follows a similar convention as defined by
map_anon_folio_pmd_(no)pf(). This not only cleans up the current
implementation of do_anonymous_page(), but will allow for reuse later in
the khugepaged mTHP implementation.

The second patch adds a small is_pmd_order() helper to check if an order
is the PMD order. This check is open-coded in a number of places. This
patch aims to clean this up and will be used more in the khugepaged mTHP
work. The third patch also adds a small DEFINE for (HPAGE_PMD_NR - 1)
which is used often across the khugepaged code.

The fourth and fifth patch come from the khugepaged mTHP patchset [1].
These two patches include the rename of function prefixes, and the
unification of khugepaged and madvise_collapse via a new
collapse_single_pmd function.

Patch 1: refactor do_anonymous_page into map_anon_folio_pte_(no)pf
Patch 2: add is_pmd_order helper
Patch 3: Add define for (HPAGE_PMD_NR - 1)
Patch 4: Refactor/rename hpage_collapse
Patch 5: Refactoring to combine madvise_collapse and khugepaged

A big thanks to everyone that has reviewed, tested, and participated in
the development process.


This patch (of 5):

The anonymous page fault handler in do_anonymous_page() open-codes the
sequence to map a newly allocated anonymous folio at the PTE level:

- construct the PTE entry
- add rmap
- add to LRU
- set the PTEs
- update the MMU cache.

Introduce two helpers to consolidate this duplicated logic, mirroring the
existing map_anon_folio_pmd_nopf() pattern for PMD-level mappings:

map_anon_folio_pte_nopf(): constructs the PTE entry, takes folio
references, adds anon rmap and LRU. This function also handles the
uffd_wp that can occur in the pf variant. The future khugepaged mTHP code
calls this to handle mapping the new collapsed mTHP to its folio.

map_anon_folio_pte_pf(): extends the nopf variant to handle MM_ANONPAGES
counter updates, and mTHP fault allocation statistics for the page fault
path.

The zero-page read path in do_anonymous_page() is also untangled from the
shared setpte label, since it does not allocate a folio and should not
share the same mapping sequence as the write path. We can now leave
nr_pages undeclared at the function intialization, and use the single page
update_mmu_cache function to handle the zero page update.

This refactoring will also help reduce code duplication between
mm/memory.c and mm/khugepaged.c, and provides a clean API for PTE-level
anonymous folio mapping that can be reused by future callers (like
khugpeaged mTHP support)

Link: https://lkml.kernel.org/r/20260325114022.444081-1-npache@redhat.com
Link: https://lkml.kernel.org/r/20260325114022.444081-2-npache@redhat.com
Link: https://lore.kernel.org/all/20260122192841.128719-1-npache@redhat.com
Signed-off-by: Nico Pache <npache@redhat.com>
Suggested-by: Lorenzo Stoakes (Oracle) <ljs@kernel.org>
Reviewed-by: Lorenzo Stoakes (Oracle) <ljs@kernel.org>
Reviewed-by: Dev Jain <dev.jain@arm.com>
Reviewed-by: Lance Yang <lance.yang@linux.dev>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Barry Song <baohua@kernel.org>
Cc: Brendan Jackman <jackmanb@google.com>
Cc: Byungchul Park <byungchul@sk.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Gregory Price <gourry@gourry.net>
Cc: "Huang, Ying" <ying.huang@linux.alibaba.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Jann Horn <jannh@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Joshua Hahn <joshua.hahnjy@gmail.com>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: "Masami Hiramatsu (Google)" <mhiramat@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Matthew Brost <matthew.brost@intel.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Nanyong Sun <sunnanyong@huawei.com>
Cc: Pedro Falcato <pfalcato@suse.de>
Cc: Peter Xu <peterx@redhat.com>
Cc: Rafael Aquini <raquini@redhat.com>
Cc: Rakie Kim <rakie.kim@sk.com>
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Shivank Garg <shivankg@amd.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Takashi Iwai (SUSE) <tiwai@suse.de>
Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Cc: Usama Arif <usamaarif642@gmail.com>
Cc: Vishal Moola (Oracle) <vishal.moola@gmail.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Wei Yang <richard.weiyang@gmail.com>
Cc: Will Deacon <will@kernel.org>
Cc: Yang Shi <yang@os.amperecomputing.com>
Cc: Zach O'Keefe <zokeefe@google.com>
Cc: Zi Yan <ziy@nvidia.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>