linux-toradex.git/mm/memory.c, branch v6.18-rc4

mm/fault: try to map the entire file folio in finish_fault()

2025-09-28T18:51:30+00:00

finish_fault() uses per-page fault for file folios.  This only occurs for
file folios smaller than PMD_SIZE.

The comment suggests that this approach prevents RSS inflation.  However,
it only prevents RSS accounting.  The folio is still mapped to the
process, and the fact that it is mapped by a single PTE does not affect
memory pressure.  Additionally, the kernel's ability to map large folios
as PMD if they are large enough does not support this argument.

When possible, map large folios in one shot.  This reduces the number of
minor page faults and allows for TLB coalescing.

Mapping large folios at once will allow the rmap code to mlock it on add,
as it will recognize that it is fully mapped and mlocking is safe.

Link: https://lkml.kernel.org/r/20250923110711.690639-5-kirill@shutemov.name
Signed-off-by: Kiryl Shutsemau 
Reviewed-by: Shakeel Butt 
Reviewed-by: Baolin Wang 
Cc: David Hildenbrand 
Cc: Johannes Weiner 
Cc: Lorenzo Stoakes 
Signed-off-by: Andrew Morton

mm: remove redundant test in validate_page_before_insert()

2025-09-21T21:22:32+00:00

The page_has_type() call would have included slab since commit
46df8e73a4a3 and now we don't even get that far because slab pages have a
zero refcount since commit 9aec2fb0fd5e.

Link: https://lkml.kernel.org/r/20250910142923.2465470-3-willy@infradead.org
Signed-off-by: Matthew Wilcox (Oracle) 
Acked-by: David Hildenbrand 
Acked-by: Vlastimil Babka 
Signed-off-by: Andrew Morton

mm, swap: cleanup swap cache API and add kerneldoc

2025-09-21T21:22:23+00:00

In preparation for replacing the swap cache backend with the swap table,
clean up and add proper kernel doc for all swap cache APIs.  Now all swap
cache APIs are well-defined with consistent names.

No feature change, only renaming and documenting.

Link: https://lkml.kernel.org/r/20250916160100.31545-9-ryncsn@gmail.com
Signed-off-by: Kairui Song 
Acked-by: Chris Li 
Reviewed-by: Barry Song 
Reviewed-by: Baolin Wang 
Acked-by: David Hildenbrand 
Suggested-by: Chris Li 
Cc: Baoquan He 
Cc: "Huang, Ying" 
Cc: Hugh Dickins 
Cc: Johannes Weiner 
Cc: Kemeng Shi 
Cc: kernel test robot 
Cc: Lorenzo Stoakes 
Cc: Matthew Wilcox (Oracle) 
Cc: Nhat Pham 
Cc: Yosry Ahmed 
Cc: Zi Yan 
Cc: SeongJae Park 
Signed-off-by: Andrew Morton

mm, swap: always lock and check the swap cache folio before use

2025-09-21T21:22:23+00:00

Swap cache lookup only increases the reference count of the returned
folio.  That's not enough to ensure a folio is stable in the swap cache,
so the folio could be removed from the swap cache at any time.  The caller
should always lock and check the folio before using it.

We have just documented this in kerneldoc, now introduce a helper for swap
cache folio verification with proper sanity checks.

Also, sanitize a few current users to use this convention and the new
helper for easier debugging.  They were not having observable problems
yet, only trivial issues like wasted CPU cycles on swapoff or reclaiming. 
They would fail in some other way, but it is still better to always follow
this convention to make things robust and make later commits easier to do.

Link: https://lkml.kernel.org/r/20250916160100.31545-6-ryncsn@gmail.com
Signed-off-by: Kairui Song 
Acked-by: David Hildenbrand 
Acked-by: Chris Li 
Acked-by: Nhat Pham 
Suggested-by: Chris Li 
Reviewed-by: Barry Song 
Cc: Baolin Wang 
Cc: Baoquan He 
Cc: "Huang, Ying" 
Cc: Hugh Dickins 
Cc: Johannes Weiner 
Cc: Kemeng Shi 
Cc: kernel test robot 
Cc: Lorenzo Stoakes 
Cc: Matthew Wilcox (Oracle) 
Cc: Yosry Ahmed 
Cc: Zi Yan 
Cc: SeongJae Park 
Signed-off-by: Andrew Morton

mm, swap: check page poison flag after locking it

2025-09-21T21:22:22+00:00

Instead of checking the poison flag only in the fast swap cache lookup
path, always check the poison flags after locking a swap cache folio.

There are two reasons to do so.

The folio is unstable and could be removed from the swap cache anytime, so
it's totally possible that the folio is no longer the backing folio of a
swap entry, and could be an irrelevant poisoned folio.  We might
mistakenly kill a faulting process.

And it's totally possible or even common for the slow swap in path
(swapin_readahead) to bring in a cached folio.  The cache folio could be
poisoned, too.  Only checking the poison flag in the fast path will miss
such folios.

The race window is tiny, so it's very unlikely to happen, though.  While
at it, also add a unlikely prefix.

Link: https://lkml.kernel.org/r/20250916160100.31545-5-ryncsn@gmail.com
Signed-off-by: Kairui Song 
Acked-by: Chris Li 
Acked-by: David Hildenbrand 
Acked-by: Nhat Pham 
Suggested-by: Chris Li 
Cc: Baolin Wang 
Cc: Baoquan He 
Cc: Barry Song 
Cc: "Huang, Ying" 
Cc: Hugh Dickins 
Cc: Johannes Weiner 
Cc: Kemeng Shi 
Cc: kernel test robot 
Cc: Lorenzo Stoakes 
Cc: Matthew Wilcox (Oracle) 
Cc: Yosry Ahmed 
Cc: Zi Yan 
Cc: SeongJae Park 
Signed-off-by: Andrew Morton

mm, swap: use unified helper for swap cache look up

2025-09-21T21:22:22+00:00

The swap cache lookup helper swap_cache_get_folio currently does readahead
updates as well, so callers that are not doing swapin from any VMA or
mapping are forced to reuse filemap helpers instead, and have to access
the swap cache space directly.

So decouple readahead update with swap cache lookup.  Move the readahead
update part into a standalone helper.  Let the caller call the readahead
update helper if they do readahead.  And convert all swap cache lookups to
use swap_cache_get_folio.

After this commit, there are only three special cases for accessing swap
cache space now: huge memory splitting, migration, and shmem replacing,
because they need to lock the XArray.  The following commits will wrap
their accesses to the swap cache too, with special helpers.

And worth noting, currently dropbehind is not supported for anon folio,
and we will never see a dropbehind folio in swap cache.  The unified
helper can be updated later to handle that.

While at it, add proper kernedoc for touched helpers.

No functional change.

Link: https://lkml.kernel.org/r/20250916160100.31545-3-ryncsn@gmail.com
Signed-off-by: Kairui Song 
Reviewed-by: Baolin Wang 
Reviewed-by: Barry Song 
Acked-by: David Hildenbrand 
Acked-by: Chris Li 
Acked-by: Nhat Pham 
Suggested-by: Chris Li 
Cc: Baoquan He 
Cc: "Huang, Ying" 
Cc: Hugh Dickins 
Cc: Johannes Weiner 
Cc: Kemeng Shi 
Cc: kernel test robot 
Cc: Lorenzo Stoakes 
Cc: Matthew Wilcox (Oracle) 
Cc: Yosry Ahmed 
Cc: Zi Yan 
Cc: SeongJae Park 
Signed-off-by: Andrew Morton

mm/huge_memory: respect MADV_COLLAPSE with PR_THP_DISABLE_EXCEPT_ADVISED

2025-09-13T23:55:05+00:00

Let's allow for making MADV_COLLAPSE succeed on areas that neither have
VM_HUGEPAGE nor VM_NOHUGEPAGE when we have THP disabled unless explicitly
advised (PR_THP_DISABLE_EXCEPT_ADVISED).

MADV_COLLAPSE is a clear advice that we want to collapse.

Note that we still respect the VM_NOHUGEPAGE flag, just like
MADV_COLLAPSE always does. So consequently, MADV_COLLAPSE is now only
refused on VM_NOHUGEPAGE with PR_THP_DISABLE_EXCEPT_ADVISED,
including for shmem.

Link: https://lkml.kernel.org/r/20250815135549.130506-4-usamaarif642@gmail.com
Co-developed-by: Usama Arif 
Signed-off-by: Usama Arif 
Signed-off-by: David Hildenbrand 
Reviewed-by: Baolin Wang 
Reviewed-by: Lorenzo Stoakes 
Reviewed-by: Zi Yan 
Cc: Arnd Bergmann 
Cc: Barry Song 
Cc: Dev Jain 
Cc: Jann Horn 
Cc: Johannes Weiner 
Cc: Jonathan Corbet 
Cc: Liam Howlett 
Cc: Mariano Pache 
Cc: Michal Hocko 
Cc: Mike Rapoport 
Cc: Rik van Riel 
Cc: Ryan Roberts 
Cc: SeongJae Park 
Cc: Shakeel Butt 
Cc: Suren Baghdasaryan 
Cc: Vlastimil Babka 
Cc: Yafang 
Signed-off-by: Andrew Morton

mm/huge_memory: convert "tva_flags" to "enum tva_type"

2025-09-13T23:55:05+00:00

When determining which THP orders are eligible for a VMA mapping, we have
previously specified tva_flags, however it turns out it is really not
necessary to treat these as flags.

Rather, we distinguish between distinct modes.

The only case where we previously combined flags was with
TVA_ENFORCE_SYSFS, but we can avoid this by observing that this is the
default, except for MADV_COLLAPSE or an edge cases in
collapse_pte_mapped_thp() and hugepage_vma_revalidate(), and adding a mode
specifically for this case - TVA_FORCED_COLLAPSE.

We have:
* smaps handling for showing "THPeligible"
* Pagefault handling
* khugepaged handling
* Forced collapse handling: primarily MADV_COLLAPSE, but also for
  an edge case in collapse_pte_mapped_thp()

Disregarding the edge cases, we only want to ignore sysfs settings only
when we are forcing a collapse through MADV_COLLAPSE, otherwise we want to
enforce it, hence this patch does the following flag to enum conversions:

* TVA_SMAPS | TVA_ENFORCE_SYSFS -> TVA_SMAPS
* TVA_IN_PF | TVA_ENFORCE_SYSFS -> TVA_PAGEFAULT
* TVA_ENFORCE_SYSFS             -> TVA_KHUGEPAGED
* 0                             -> TVA_FORCED_COLLAPSE

With this change, we immediately know if we are in the forced collapse
case, which will be valuable next.

Link: https://lkml.kernel.org/r/20250815135549.130506-3-usamaarif642@gmail.com
Signed-off-by: David Hildenbrand 
Signed-off-by: Usama Arif 
Acked-by: Usama Arif 
Reviewed-by: Baolin Wang 
Reviewed-by: Lorenzo Stoakes 
Reviewed-by: Zi Yan 
Cc: Arnd Bergmann 
Cc: Barry Song 
Cc: Dev Jain 
Cc: Jann Horn 
Cc: Johannes Weiner 
Cc: Jonathan Corbet 
Cc: Liam Howlett 
Cc: Mariano Pache 
Cc: Michal Hocko 
Cc: Mike Rapoport 
Cc: Rik van Riel 
Cc: Ryan Roberts 
Cc: SeongJae Park 
Cc: Shakeel Butt 
Cc: Suren Baghdasaryan 
Cc: Vlastimil Babka 
Cc: Yafang 
Signed-off-by: Andrew Morton

mm: rename vm_ops->find_special_page() to vm_ops->find_normal_page()

2025-09-13T23:54:53+00:00

...  and hide it behind a kconfig option.  There is really no need for any
!xen code to perform this check.

The naming is a bit off: we want to find the "normal" page when a PTE was
marked "special".  So it's really not "finding a special" page.

Improve the documentation, and add a comment in the code where XEN ends up
performing the pte_mkspecial() through a hypercall.  More details can be
found in commit 923b2919e2c3 ("xen/gntdev: mark userspace PTEs as special
on x86 PV guests").

Link: https://lkml.kernel.org/r/20250811112631.759341-12-david@redhat.com
Signed-off-by: David Hildenbrand 
Reviewed-by: Oscar Salvador 
Reviewed-by: Lorenzo Stoakes 
Reviewed-by: Wei Yang 
Cc: David Vrabel 
Cc: Alistair Popple 
Cc: Al Viro 
Cc: Baolin Wang 
Cc: Barry Song 
Cc: Christian Brauner 
Cc: Christophe Leroy 
Cc: Dan Williams 
Cc: Dev Jain 
Cc: Hugh Dickins 
Cc: Jan Kara 
Cc: Jann Horn 
Cc: Juegren Gross 
Cc: Lance Yang 
Cc: Liam Howlett 
Cc: Madhavan Srinivasan 
Cc: Mariano Pache 
Cc: Matthew Wilcox (Oracle) 
Cc: Michael Ellerman 
Cc: Michal Hocko 
Cc: Mike Rapoport 
Cc: Nicholas Piggin 
Cc: Oleksandr Tyshchenko 
Cc: Ryan Roberts 
Cc: Stefano Stabellini 
Cc: Suren Baghdasaryan 
Cc: Vlastimil Babka 
Cc: Zi Yan 
Signed-off-by: Andrew Morton

mm: introduce and use vm_normal_page_pud()

2025-09-13T23:54:52+00:00

Let's introduce vm_normal_page_pud(), which ends up being fairly simple
because of our new common helpers and there not being a PUD-sized zero
folio.

Use vm_normal_page_pud() in folio_walk_start() to resolve a TODO,
structuring the code like the other (pmd/pte) cases.  Defer introducing
vm_normal_folio_pud() until really used.

Note that we can so far get PUDs with hugetlb, daxfs and PFNMAP entries.

Link: https://lkml.kernel.org/r/20250811112631.759341-11-david@redhat.com
Reviewed-by: Wei Yang 
Reviewed-by: Oscar Salvador 
Signed-off-by: David Hildenbrand 
Reviewed-by: Lorenzo Stoakes 
Cc: Alistair Popple 
Cc: Al Viro 
Cc: Baolin Wang 
Cc: Barry Song 
Cc: Christian Brauner 
Cc: Christophe Leroy 
Cc: Dan Williams 
Cc: David Vrabel 
Cc: Dev Jain 
Cc: Hugh Dickins 
Cc: Jan Kara 
Cc: Jann Horn 
Cc: Juegren Gross 
Cc: Lance Yang 
Cc: Liam Howlett 
Cc: Madhavan Srinivasan 
Cc: Mariano Pache 
Cc: Matthew Wilcox (Oracle) 
Cc: Michael Ellerman 
Cc: Michal Hocko 
Cc: Mike Rapoport 
Cc: Nicholas Piggin 
Cc: Oleksandr Tyshchenko 
Cc: Ryan Roberts 
Cc: Stefano Stabellini 
Cc: Suren Baghdasaryan 
Cc: Vlastimil Babka 
Cc: Zi Yan 
Signed-off-by: Andrew Morton