linux.git/mm/huge_memory.c, branch v6.17

mm/huge_memory: refactor after-split (page) cache code

2025-07-25T02:12:39+00:00

Smatch/coverity checkers report NULL mapping referencing issues[1][2][3]
every time the code is modified, because they do not understand that
mapping cannot be NULL when a folio is in page cache in the code. 
Refactor the code to make it explicit.

Remove "end = -1" for anonymous folios, since after code refactoring, end
is no longer used by anonymous folio handling code.

No functional change is intended.

Link: https://lkml.kernel.org/r/20250718023000.4044406-7-ziy@nvidia.com
Link: https://lore.kernel.org/linux-mm/2afe3d59-aca5-40f7-82a3-a6d976fb0f4f@stanley.mountain/ [1]
Link: https://lore.kernel.org/oe-kbuild/64b54034-f311-4e7d-b935-c16775dbb642@suswa.mountain/ [2]
Link: https://lore.kernel.org/linux-mm/20250716145804.4836-1-antonio@mandelbit.com/ [3]
Link: https://lkml.kernel.org/r/20250718183720.4054515-7-ziy@nvidia.com
Signed-off-by: Zi Yan 
Suggested-by: David Hildenbrand 
Acked-by: David Hildenbrand 
Reviewed-by: Lorenzo Stoakes 
Cc: Balbir Singh 
Cc: Baolin Wang 
Cc: Barry Song 
Cc: Dan Carpenter 
Cc: Dev Jain 
Cc: Hugh Dickins 
Cc: Kirill A. Shutemov 
Cc: Liam Howlett 
Cc: Mariano Pache 
Cc: Mathew Brost 
Cc: Ryan Roberts 
Signed-off-by: Andrew Morton

mm/huge_memory: get frozen folio refcount with folio_expected_ref_count()

2025-07-25T02:12:39+00:00

Instead of open coding the refcount calculation, use
folio_expected_ref_count() to calculate frozen folio refcount.  Because:

1. __folio_split() does not split a folio with PG_private, so no elevated
   refcount from PG_private;
2. a frozen folio in __folio_split() is fully unmapped, so folio_mapcount()
   in folio_expected_ref_count() is always 0;
3. (mapping || swap_cache) ? folio_nr_pages(folio) is taken care of by
   folio_expected_ref_count() too.

Link: https://lkml.kernel.org/r/20250718023000.4044406-6-ziy@nvidia.com
Link: https://lkml.kernel.org/r/20250718183720.4054515-6-ziy@nvidia.com
Signed-off-by: Zi Yan 
Suggested-by: David Hildenbrand 
Acked-by: Balbir Singh 
Acked-by: David Hildenbrand 
Reviewed-by: Lorenzo Stoakes 
Cc: Antonio Quartulli 
Cc: Baolin Wang 
Cc: Barry Song 
Cc: Dan Carpenter 
Cc: Dev Jain 
Cc: Hugh Dickins 
Cc: Kirill A. Shutemov 
Cc: Liam Howlett 
Cc: Mariano Pache 
Cc: Mathew Brost 
Cc: Ryan Roberts 
Signed-off-by: Andrew Morton

mm/huge_memory: convert VM_BUG* to VM_WARN* in __folio_split

2025-07-25T02:12:39+00:00

These VM_BUG* can be handled gracefully without crashing kernel.

Link: https://lkml.kernel.org/r/20250718023000.4044406-5-ziy@nvidia.com
Link: https://lkml.kernel.org/r/20250718183720.4054515-5-ziy@nvidia.com
Signed-off-by: Zi Yan 
Reviewed-by: Lorenzo Stoakes 
Acked-by: David Hildenbrand 
Cc: Antonio Quartulli 
Cc: Balbir Singh 
Cc: Baolin Wang 
Cc: Barry Song 
Cc: Dan Carpenter 
Cc: Dev Jain 
Cc: Hugh Dickins 
Cc: Kirill A. Shutemov 
Cc: Liam Howlett 
Cc: Mariano Pache 
Cc: Mathew Brost 
Cc: Ryan Roberts 
Signed-off-by: Andrew Morton

mm/huge_memory: deduplicate code in __folio_split()

2025-07-25T02:12:39+00:00

xas unlock, remap_page(), local_irq_enable() are moved out of if branches
to deduplicate the code.  While at it, add remap_flags to clean up
remap_page() call site.  nr_dropped is renamed to nr_shmem_dropped, as it
becomes a variable at __folio_split() scope.

Link: https://lkml.kernel.org/r/20250718183720.4054515-4-ziy@nvidia.com
Signed-off-by: Zi Yan 
Acked-by: David Hildenbrand 
Reviewed-by: Lorenzo Stoakes 
Cc: Antonio Quartulli 
Cc: Balbir Singh 
Cc: Baolin Wang 
Cc: Barry Song 
Cc: Dan Carpenter 
Cc: Dev Jain 
Cc: Hugh Dickins 
Cc: Kirill A. Shutemov 
Cc: Liam Howlett 
Cc: Mariano Pache 
Cc: Mathew Brost 
Cc: Ryan Roberts 
Signed-off-by: Andrew Morton

mm/huge_memory: remove after_split label in __split_unmapped_folio()

2025-07-25T02:12:38+00:00

Check stop_split instead to avoid the goto statement.

Link: https://lkml.kernel.org/r/20250718183720.4054515-3-ziy@nvidia.com
Signed-off-by: Zi Yan 
Acked-by: David Hildenbrand 
Reviewed-by: Lorenzo Stoakes 
Cc: Antonio Quartulli 
Cc: Balbir Singh 
Cc: Baolin Wang 
Cc: Barry Song 
Cc: Dan Carpenter 
Cc: Dev Jain 
Cc: Hugh Dickins 
Cc: Kirill A. Shutemov 
Cc: Liam Howlett 
Cc: Mariano Pache 
Cc: Mathew Brost 
Cc: Ryan Roberts 
Signed-off-by: Andrew Morton

mm/huge_memory: move unrelated code out of __split_unmapped_folio()

2025-07-25T02:12:38+00:00

Patch series "__folio_split() clean up", v5.

This patchset refactors __folio_split() and __split_unmapped_folio() to:
1. make __split_unmapped_folio() reusable for splitting unmapped
   folios.  It avoids the need for a new boolean unmapped parameter to
   guard mapping-related code when __split_unmapped_folio() is reused to
   split unmapped folios.
2. improve code readability and prevent smatch/coverity checkers from
   complaining about NULL mapping referencing.

An additional benefit for __split_unmapped_folio() refactoring is that
__split_unmapped_folio() could be called on after-split folios by
__folio_split().  It can enable new split methods.  For example, at
deferred split time, unmapped subpages can scatter arbitrarily within a
large folio, neither uniform nor non-uniform split can maximize
after-split folio orders for mapped subpages.  The hope is that by calling
__split_unmapped_folio() multiple times, a better split result can be
achieved.


This patch (of 6):

remap(), folio_ref_unfreeze(), lru_add_split_folio() are not relevant to
splitting unmapped folio operations.  Move them out to __folio_split() so
that __split_unmapped_folio() only handles unmapped folio splits.  This
makes __split_unmapped_folio() reusable.

Remove the swapcache folio split check code before
__split_unmapped_folio() call, since it is already checked at the
beginning of __folio_split() in uniform_split_supported() and
non_uniform_split_supported().

Along with the code move, there are some variable renames:

1. release is renamed to new_folio,
2. origin_folio is now folio, since __folio_split() has folio pointing to
   the original folio already.

Link: https://lkml.kernel.org/r/20250718023000.4044406-1-ziy@nvidia.com
Link: https://lkml.kernel.org/r/20250718023000.4044406-2-ziy@nvidia.com
Link: https://lkml.kernel.org/r/20250718183720.4054515-1-ziy@nvidia.com
Link: https://lkml.kernel.org/r/20250718183720.4054515-2-ziy@nvidia.com
Signed-off-by: Zi Yan 
Acked-by: David Hildenbrand 
Reviewed-by: Lorenzo Stoakes 
Cc: Antonio Quartulli 
Cc: Balbir Singh 
Cc: Baolin Wang 
Cc: Barry Song 
Cc: Dan Carpenter 
Cc: Dev Jain 
Cc: Hugh Dickins 
Cc: Kirill A. Shutemov 
Cc: Liam Howlett 
Cc: Mariano Pache 
Cc: Mathew Brost 
Cc: Ryan Roberts 
Cc: Zi Yan 
Signed-off-by: Andrew Morton

mm: remove callers of pfn_t functionality

2025-07-10T05:42:19+00:00

All PFN_* pfn_t flags have been removed.  Therefore there is no longer a
need for the pfn_t type and all uses can be replaced with normal pfns.

Link: https://lkml.kernel.org/r/bbedfa576c9822f8032494efbe43544628698b1f.1750323463.git-series.apopple@nvidia.com
Signed-off-by: Alistair Popple 
Reviewed-by: Christoph Hellwig 
Reviewed-by: Jason Gunthorpe 
Acked-by: David Hildenbrand 
Cc: Balbir Singh 
Cc: Björn Töpel 
Cc: Björn Töpel 
Cc: Chunyan Zhang 
Cc: Dan Williams 
Cc: Deepak Gupta 
Cc: Gerald Schaefer 
Cc: Inki Dae 
Cc: John Groves 
Cc: John Hubbard 
Cc: Lorenzo Stoakes 
Cc: Matthew Wilcox (Oracle) 
Cc: Will Deacon 
Signed-off-by: Andrew Morton

mm: remove redundant pXd_devmap calls

2025-07-10T05:42:17+00:00

DAX was the only thing that created pmd_devmap and pud_devmap entries
however it no longer does as DAX pages are now refcounted normally and
pXd_trans_huge() returns true for those.  Therefore checking both
pXd_devmap and pXd_trans_huge() is redundant and the former can be removed
without changing behaviour as it will always be false.

Link: https://lkml.kernel.org/r/d58f089dc16b7feb7c6728164f37dea65d64a0d3.1750323463.git-series.apopple@nvidia.com
Signed-off-by: Alistair Popple 
Cc: Balbir Singh 
Cc: Björn Töpel 
Cc: Björn Töpel 
Cc: Christoph Hellwig 
Cc: Chunyan Zhang 
Cc: Dan Williams 
Cc: David Hildenbrand 
Cc: Deepak Gupta 
Cc: Gerald Schaefer 
Cc: Inki Dae 
Cc: Jason Gunthorpe 
Cc: John Groves 
Cc: John Hubbard 
Cc: Lorenzo Stoakes 
Cc: Matthew Wilcox (Oracle) 
Cc: Will Deacon 
Signed-off-by: Andrew Morton

mm/huge_memory: remove pXd_devmap usage from insert_pXd_pfn()

2025-07-10T05:42:17+00:00

Nothing uses PFN_DEV anymore so no need to create devmap pXd's when
mapping a PFN.  Instead special mappings will be created which ensures
vm_normal_page_pXd() will not return pages which don't have an associated
page.  This could change behaviour slightly on architectures where
pXd_devmap() does not imply pXd_special() as the normal page checks would
have fallen through to checking VM_PFNMAP/MIXEDMAP instead, which in
theory at least could have returned a page.

However vm_normal_page_pXd() should never have been returning pages for
pXd_devmap() entries anyway, so anything relying on that would have been a
bug.

Link: https://lkml.kernel.org/r/cd8658f9ff10afcfffd8b145a39d98bf1c595ffa.1750323463.git-series.apopple@nvidia.com
Signed-off-by: Alistair Popple 
Cc: Balbir Singh 
Cc: Björn Töpel 
Cc: Björn Töpel 
Cc: Christoph Hellwig 
Cc: Chunyan Zhang 
Cc: Dan Williams 
Cc: David Hildenbrand 
Cc: Deepak Gupta 
Cc: Gerald Schaefer 
Cc: Inki Dae 
Cc: Jason Gunthorpe 
Cc: John Groves 
Cc: John Hubbard 
Cc: Lorenzo Stoakes 
Cc: Matthew Wilcox (Oracle) 
Cc: Will Deacon 
Signed-off-by: Andrew Morton

mm/gup: remove pXX_devmap usage from get_user_pages()

2025-07-10T05:42:16+00:00

GUP uses pXX_devmap() calls to see if it needs to a get a reference on the
associated pgmap data structure to ensure the pages won't go away. 
However it's a driver responsibility to ensure that if pages are mapped
(ie.  discoverable by GUP) that they are not offlined or removed from the
memmap so there is no need to hold a reference on the pgmap data structure
to ensure this.

Furthermore mappings with PFN_DEV are no longer created, hence this
effectively dead code anyway so can be removed.

Link: https://lkml.kernel.org/r/708b2be76876659ec5261fe5d059b07268b98b36.1750323463.git-series.apopple@nvidia.com
Signed-off-by: Alistair Popple 
Reviewed-by: Jason Gunthorpe 
Reviewed-by: Dan Williams 
Cc: Balbir Singh 
Cc: Björn Töpel 
Cc: Björn Töpel 
Cc: Christoph Hellwig 
Cc: Chunyan Zhang 
Cc: David Hildenbrand 
Cc: Deepak Gupta 
Cc: Gerald Schaefer 
Cc: Inki Dae 
Cc: John Groves 
Cc: John Hubbard 
Cc: Lorenzo Stoakes 
Cc: Matthew Wilcox (Oracle) 
Cc: Will Deacon 
Signed-off-by: Andrew Morton