Merge tag 'mm-stable-2023-04-27-15-30' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

Pull MM updates from Andrew Morton:

 - Nick Piggin's "shoot lazy tlbs" series, to improve the peformance of
   switching from a user process to a kernel thread.

 - More folio conversions from Kefeng Wang, Zhang Peng and Pankaj
   Raghav.

 - zsmalloc performance improvements from Sergey Senozhatsky.

 - Yue Zhao has found and fixed some data race issues around the
   alteration of memcg userspace tunables.

 - VFS rationalizations from Christoph Hellwig:
     - removal of most of the callers of write_one_page()
     - make __filemap_get_folio()'s return value more useful

 - Luis Chamberlain has changed tmpfs so it no longer requires swap
   backing. Use `mount -o noswap'.

 - Qi Zheng has made the slab shrinkers operate locklessly, providing
   some scalability benefits.

 - Keith Busch has improved dmapool's performance, making part of its
   operations O(1) rather than O(n).

 - Peter Xu adds the UFFD_FEATURE_WP_UNPOPULATED feature to userfaultd,
   permitting userspace to wr-protect anon memory unpopulated ptes.

 - Kirill Shutemov has changed MAX_ORDER's meaning to be inclusive
   rather than exclusive, and has fixed a bunch of errors which were
   caused by its unintuitive meaning.

 - Axel Rasmussen give userfaultfd the UFFDIO_CONTINUE_MODE_WP feature,
   which causes minor faults to install a write-protected pte.

 - Vlastimil Babka has done some maintenance work on vma_merge():
   cleanups to the kernel code and improvements to our userspace test
   harness.

 - Cleanups to do_fault_around() by Lorenzo Stoakes.

 - Mike Rapoport has moved a lot of initialization code out of various
   mm/ files and into mm/mm_init.c.

 - Lorenzo Stoakes removd vmf_insert_mixed_prot(), which was added for
   DRM, but DRM doesn't use it any more.

 - Lorenzo has also coverted read_kcore() and vread() to use iterators
   and has thereby removed the use of bounce buffers in some cases.

 - Lorenzo has also contributed further cleanups of vma_merge().

 - Chaitanya Prakash provides some fixes to the mmap selftesting code.

 - Matthew Wilcox changes xfs and afs so they no longer take sleeping
   locks in ->map_page(), a step towards RCUification of pagefaults.

 - Suren Baghdasaryan has improved mmap_lock scalability by switching to
   per-VMA locking.

 - Frederic Weisbecker has reworked the percpu cache draining so that it
   no longer causes latency glitches on cpu isolated workloads.

 - Mike Rapoport cleans up and corrects the ARCH_FORCE_MAX_ORDER Kconfig
   logic.

 - Liu Shixin has changed zswap's initialization so we no longer waste a
   chunk of memory if zswap is not being used.

 - Yosry Ahmed has improved the performance of memcg statistics
   flushing.

 - David Stevens has fixed several issues involving khugepaged,
   userfaultfd and shmem.

 - Christoph Hellwig has provided some cleanup work to zram's IO-related
   code paths.

 - David Hildenbrand has fixed up some issues in the selftest code's
   testing of our pte state changing.

 - Pankaj Raghav has made page_endio() unneeded and has removed it.

 - Peter Xu contributed some rationalizations of the userfaultfd
   selftests.

 - Yosry Ahmed has fixed an issue around memcg's page recalim
   accounting.

 - Chaitanya Prakash has fixed some arm-related issues in the
   selftests/mm code.

 - Longlong Xia has improved the way in which KSM handles hwpoisoned
   pages.

 - Peter Xu fixes a few issues with uffd-wp at fork() time.

 - Stefan Roesch has changed KSM so that it may now be used on a
   per-process and per-cgroup basis.

* tag 'mm-stable-2023-04-27-15-30' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm: (369 commits)
  mm,unmap: avoid flushing TLB in batch if PTE is inaccessible
  shmem: restrict noswap option to initial user namespace
  mm/khugepaged: fix conflicting mods to collapse_file()
  sparse: remove unnecessary 0 values from rc
  mm: move 'mmap_min_addr' logic from callers into vm_unmapped_area()
  hugetlb: pte_alloc_huge() to replace huge pte_alloc_map()
  maple_tree: fix allocation in mas_sparse_area()
  mm: do not increment pgfault stats when page fault handler retries
  zsmalloc: allow only one active pool compaction context
  selftests/mm: add new selftests for KSM
  mm: add new KSM process and sysfs knobs
  mm: add new api to enable ksm per process
  mm: shrinkers: fix debugfs file permissions
  mm: don't check VMA write permissions if the PTE/PMD indicates write permissions
  migrate_pages_batch: fix statistics for longterm pin retry
  userfaultfd: use helper function range_in_vma()
  lib/show_mem.c: use for_each_populated_zone() simplify code
  mm: correct arg in reclaim_pages()/reclaim_clean_pages_from_list()
  fs/buffer: convert create_page_buffers to folio_create_buffers
  fs/buffer: add folio_create_empty_buffers helper
  ...

Documentation/ABI/testing/sysfs-kernel-mm-ksm

@@ -51,3 +51,11 @@ Description:	Control merging pages across different NUMA nodes.
 
 		When it is set to 0 only pages from the same node are merged,
 		otherwise pages from all nodes can be merged together (default).
+
+What:		/sys/kernel/mm/ksm/general_profit
+Date:		April 2023
+KernelVersion:  6.4
+Contact:	Linux memory management mailing list <linux-mm@kvack.org>
+Description:	Measure how effective KSM is.
+		general_profit: how effective is KSM. The formula for the
+		calculation is in Documentation/admin-guide/mm/ksm.rst.

Documentation/admin-guide/kdump/vmcoreinfo.rst

@@ -172,7 +172,7 @@ variables.
 Offset of the free_list's member. This value is used to compute the number
 of free pages.
 
-Each zone has a free_area structure array called free_area[MAX_ORDER].
+Each zone has a free_area structure array called free_area[MAX_ORDER + 1].
 The free_list represents a linked list of free page blocks.
 
 (list_head, next|prev)
@@ -189,8 +189,8 @@ Offsets of the vmap_area's members. They carry vmalloc-specific
 information. Makedumpfile gets the start address of the vmalloc region
 from this.
 
-(zone.free_area, MAX_ORDER)
----------------------------
+(zone.free_area, MAX_ORDER + 1)
+-------------------------------
 
 Free areas descriptor. User-space tools use this value to iterate the
 free_area ranges. MAX_ORDER is used by the zone buddy allocator.

Documentation/admin-guide/kernel-parameters.txt

@@ -4012,7 +4012,7 @@
 			[KNL] Minimal page reporting order
 			Format: <integer>
 			Adjust the minimal page reporting order. The page
-			reporting is disabled when it exceeds (MAX_ORDER-1).
+			reporting is disabled when it exceeds MAX_ORDER.
 
 	panic=		[KNL] Kernel behaviour on panic: delay <timeout>
 			timeout > 0: seconds before rebooting

Documentation/admin-guide/mm/ksm.rst

@@ -157,6 +157,8 @@ stable_node_chains_prune_millisecs
 
 The effectiveness of KSM and MADV_MERGEABLE is shown in ``/sys/kernel/mm/ksm/``:
 
+general_profit
+        how effective is KSM. The calculation is explained below.
 pages_shared
         how many shared pages are being used
 pages_sharing
@@ -207,7 +209,8 @@ several times, which are unprofitable memory consumed.
 			  ksm_rmap_items * sizeof(rmap_item).
 
    where ksm_merging_pages is shown under the directory ``/proc/<pid>/``,
-   and ksm_rmap_items is shown in ``/proc/<pid>/ksm_stat``.
+   and ksm_rmap_items is shown in ``/proc/<pid>/ksm_stat``. The process profit
+   is also shown in ``/proc/<pid>/ksm_stat`` as ksm_process_profit.
 
 From the perspective of application, a high ratio of ``ksm_rmap_items`` to
 ``ksm_merging_pages`` means a bad madvise-applied policy, so developers or

Documentation/admin-guide/mm/userfaultfd.rst

@@ -219,6 +219,31 @@ former will have ``UFFD_PAGEFAULT_FLAG_WP`` set, the latter
 you still need to supply a page when ``UFFDIO_REGISTER_MODE_MISSING`` was
 used.
 
+Userfaultfd write-protect mode currently behave differently on none ptes
+(when e.g. page is missing) over different types of memories.
+
+For anonymous memory, ``ioctl(UFFDIO_WRITEPROTECT)`` will ignore none ptes
+(e.g. when pages are missing and not populated).  For file-backed memories
+like shmem and hugetlbfs, none ptes will be write protected just like a
+present pte.  In other words, there will be a userfaultfd write fault
+message generated when writing to a missing page on file typed memories,
+as long as the page range was write-protected before.  Such a message will
+not be generated on anonymous memories by default.
+
+If the application wants to be able to write protect none ptes on anonymous
+memory, one can pre-populate the memory with e.g. MADV_POPULATE_READ.  On
+newer kernels, one can also detect the feature UFFD_FEATURE_WP_UNPOPULATED
+and set the feature bit in advance to make sure none ptes will also be
+write protected even upon anonymous memory.
+
+When using ``UFFDIO_REGISTER_MODE_WP`` in combination with either
+``UFFDIO_REGISTER_MODE_MISSING`` or ``UFFDIO_REGISTER_MODE_MINOR``, when
+resolving missing / minor faults with ``UFFDIO_COPY`` or ``UFFDIO_CONTINUE``
+respectively, it may be desirable for the new page / mapping to be
+write-protected (so future writes will also result in a WP fault). These ioctls
+support a mode flag (``UFFDIO_COPY_MODE_WP`` or ``UFFDIO_CONTINUE_MODE_WP``
+respectively) to configure the mapping this way.
+
 QEMU/KVM
 ========
 

Documentation/core-api/printk-formats.rst

@@ -575,20 +575,26 @@ The field width is passed by value, the bitmap is passed by reference.
 Helper macros cpumask_pr_args() and nodemask_pr_args() are available to ease
 printing cpumask and nodemask.
 
-Flags bitfields such as page flags, gfp_flags
----------------------------------------------
+Flags bitfields such as page flags, page_type, gfp_flags
+--------------------------------------------------------
 
 ::
 
 	%pGp	0x17ffffc0002036(referenced|uptodate|lru|active|private|node=0|zone=2|lastcpupid=0x1fffff)
+	%pGt	0xffffff7f(buddy)
 	%pGg	GFP_USER|GFP_DMA32|GFP_NOWARN
 	%pGv	read|exec|mayread|maywrite|mayexec|denywrite
 
 For printing flags bitfields as a collection of symbolic constants that
 would construct the value. The type of flags is given by the third
-character. Currently supported are [p]age flags, [v]ma_flags (both
-expect ``unsigned long *``) and [g]fp_flags (expects ``gfp_t *``). The flag
-names and print order depends on the particular	type.
+character. Currently supported are:
+
+        - p - [p]age flags, expects value of type (``unsigned long *``)
+        - t - page [t]ype, expects value of type (``unsigned int *``)
+        - v - [v]ma_flags, expects value of type (``unsigned long *``)
+        - g - [g]fp_flags, expects value of type (``gfp_t *``)
+
+The flag names and print order depends on the particular type.
 
 Note that this format should not be used directly in the
 :c:func:`TP_printk()` part of a tracepoint. Instead, use the show_*_flags()

Documentation/filesystems/locking.rst

@@ -645,7 +645,7 @@ ops		mmap_lock	PageLocked(page)
 open:		yes
 close:		yes
 fault:		yes		can return with page locked
-map_pages:	yes
+map_pages:	read
 page_mkwrite:	yes		can return with page locked
 pfn_mkwrite:	yes
 access:		yes
@@ -661,7 +661,7 @@ locked. The VM will unlock the page.
 
 ->map_pages() is called when VM asks to map easy accessible pages.
 Filesystem should find and map pages associated with offsets from "start_pgoff"
-till "end_pgoff". ->map_pages() is called with page table locked and must
+till "end_pgoff". ->map_pages() is called with the RCU lock held and must
 not block.  If it's not possible to reach a page without blocking,
 filesystem should skip it. Filesystem should use do_set_pte() to setup
 page table entry. Pointer to entry associated with the page is passed in

Documentation/filesystems/proc.rst

@@ -996,6 +996,7 @@ Example output. You may not have all of these fields.
     VmallocUsed:       40444 kB
     VmallocChunk:          0 kB
     Percpu:            29312 kB
+    EarlyMemtestBad:       0 kB
     HardwareCorrupted:     0 kB
     AnonHugePages:   4149248 kB
     ShmemHugePages:        0 kB
@@ -1146,6 +1147,13 @@ VmallocChunk
 Percpu
               Memory allocated to the percpu allocator used to back percpu
               allocations. This stat excludes the cost of metadata.
+EarlyMemtestBad
+              The amount of RAM/memory in kB, that was identified as corrupted
+              by early memtest. If memtest was not run, this field will not
+              be displayed at all. Size is never rounded down to 0 kB.
+              That means if 0 kB is reported, you can safely assume
+              there was at least one pass of memtest and none of the passes
+              found a single faulty byte of RAM.
 HardwareCorrupted
               The amount of RAM/memory in KB, the kernel identifies as
               corrupted.

Documentation/filesystems/tmpfs.rst

@@ -13,17 +13,29 @@ everything stored therein is lost.
 
 tmpfs puts everything into the kernel internal caches and grows and
 shrinks to accommodate the files it contains and is able to swap
-unneeded pages out to swap space. It has maximum size limits which can
-be adjusted on the fly via 'mount -o remount ...'
+unneeded pages out to swap space, if swap was enabled for the tmpfs
+mount. tmpfs also supports THP.
 
-If you compare it to ramfs (which was the template to create tmpfs)
-you gain swapping and limit checking. Another similar thing is the RAM
-disk (/dev/ram*), which simulates a fixed size hard disk in physical
-RAM, where you have to create an ordinary filesystem on top. Ramdisks
-cannot swap and you do not have the possibility to resize them.
+tmpfs extends ramfs with a few userspace configurable options listed and
+explained further below, some of which can be reconfigured dynamically on the
+fly using a remount ('mount -o remount ...') of the filesystem. A tmpfs
+filesystem can be resized but it cannot be resized to a size below its current
+usage. tmpfs also supports POSIX ACLs, and extended attributes for the
+trusted.* and security.* namespaces. ramfs does not use swap and you cannot
+modify any parameter for a ramfs filesystem. The size limit of a ramfs
+filesystem is how much memory you have available, and so care must be taken if
+used so to not run out of memory.
 
-Since tmpfs lives completely in the page cache and on swap, all tmpfs
-pages will be shown as "Shmem" in /proc/meminfo and "Shared" in
+An alternative to tmpfs and ramfs is to use brd to create RAM disks
+(/dev/ram*), which allows you to simulate a block device disk in physical RAM.
+To write data you would just then need to create an regular filesystem on top
+this ramdisk. As with ramfs, brd ramdisks cannot swap. brd ramdisks are also
+configured in size at initialization and you cannot dynamically resize them.
+Contrary to brd ramdisks, tmpfs has its own filesystem, it does not rely on the
+block layer at all.
+
+Since tmpfs lives completely in the page cache and optionally on swap,
+all tmpfs pages will be shown as "Shmem" in /proc/meminfo and "Shared" in
 free(1). Notice that these counters also include shared memory
 (shmem, see ipcs(1)). The most reliable way to get the count is
 using df(1) and du(1).
@@ -72,6 +84,8 @@ nr_inodes  The maximum number of inodes for this instance. The default
            is half of the number of your physical RAM pages, or (on a
            machine with highmem) the number of lowmem RAM pages,
            whichever is the lower.
+noswap     Disables swap. Remounts must respect the original settings.
+           By default swap is enabled.
 =========  ============================================================
 
 These parameters accept a suffix k, m or g for kilo, mega and giga and
@@ -85,6 +99,36 @@ mount with such options, since it allows any user with write access to
 use up all the memory on the machine; but enhances the scalability of
 that instance in a system with many CPUs making intensive use of it.
 
+tmpfs also supports Transparent Huge Pages which requires a kernel
+configured with CONFIG_TRANSPARENT_HUGEPAGE and with huge supported for
+your system (has_transparent_hugepage(), which is architecture specific).
+The mount options for this are:
+
+======  ============================================================
+huge=0  never: disables huge pages for the mount
+huge=1  always: enables huge pages for the mount
+huge=2  within_size: only allocate huge pages if the page will be
+        fully within i_size, also respect fadvise()/madvise() hints.
+huge=3  advise: only allocate huge pages if requested with
+        fadvise()/madvise()
+======  ============================================================
+
+There is a sysfs file which you can also use to control system wide THP
+configuration for all tmpfs mounts, the file is:
+
+/sys/kernel/mm/transparent_hugepage/shmem_enabled
+
+This sysfs file is placed on top of THP sysfs directory and so is registered
+by THP code. It is however only used to control all tmpfs mounts with one
+single knob. Since it controls all tmpfs mounts it should only be used either
+for emergency or testing purposes. The values you can set for shmem_enabled are:
+
+==  ============================================================
+-1  deny: disables huge on shm_mnt and all mounts, for
+    emergency use
+-2  force: enables huge on shm_mnt and all mounts, w/o needing
+    option, for testing
+==  ============================================================
 
 tmpfs has a mount option to set the NUMA memory allocation policy for
 all files in that instance (if CONFIG_NUMA is enabled) - which can be

Documentation/mm/active_mm.rst

@@ -2,6 +2,12 @@
 Active MM
 =========
 
+Note, the mm_count refcount may no longer include the "lazy" users
+(running tasks with ->active_mm == mm && ->mm == NULL) on kernels
+with CONFIG_MMU_LAZY_TLB_REFCOUNT=n. Taking and releasing these lazy
+references must be done with mmgrab_lazy_tlb() and mmdrop_lazy_tlb()
+helpers, which abstract this config option.
+
 ::
 
  List:       linux-kernel

Documentation/mm/arch_pgtable_helpers.rst

@@ -214,7 +214,7 @@ HugeTLB Page Table Helpers
 +---------------------------+--------------------------------------------------+
 | pte_huge                  | Tests a HugeTLB                                  |
 +---------------------------+--------------------------------------------------+
-| pte_mkhuge                | Creates a HugeTLB                                |
+| arch_make_huge_pte        | Creates a HugeTLB                                |
 +---------------------------+--------------------------------------------------+
 | huge_pte_dirty            | Tests a dirty HugeTLB                            |
 +---------------------------+--------------------------------------------------+

Documentation/mm/multigen_lru.rst

@@ -103,7 +103,8 @@ moving across tiers only involves atomic operations on
 ``folio->flags`` and therefore has a negligible cost. A feedback loop
 modeled after the PID controller monitors refaults over all the tiers
 from anon and file types and decides which tiers from which types to
-evict or protect.
+evict or protect. The desired effect is to balance refault percentages
+between anon and file types proportional to the swappiness level.
 
 There are two conceptually independent procedures: the aging and the
 eviction. They form a closed-loop system, i.e., the page reclaim.
@@ -156,6 +157,27 @@ This time-based approach has the following advantages:
    and memory sizes.
 2. It is more reliable because it is directly wired to the OOM killer.
 
+``mm_struct`` list
+------------------
+An ``mm_struct`` list is maintained for each memcg, and an
+``mm_struct`` follows its owner task to the new memcg when this task
+is migrated.
+
+A page table walker iterates ``lruvec_memcg()->mm_list`` and calls
+``walk_page_range()`` with each ``mm_struct`` on this list to scan
+PTEs. When multiple page table walkers iterate the same list, each of
+them gets a unique ``mm_struct``, and therefore they can run in
+parallel.
+
+Page table walkers ignore any misplaced pages, e.g., if an
+``mm_struct`` was migrated, pages left in the previous memcg will be
+ignored when the current memcg is under reclaim. Similarly, page table
+walkers will ignore pages from nodes other than the one under reclaim.
+
+This infrastructure also tracks the usage of ``mm_struct`` between
+context switches so that page table walkers can skip processes that
+have been sleeping since the last iteration.
+
 Rmap/PT walk feedback
 ---------------------
 Searching the rmap for PTEs mapping each page on an LRU list (to test
@@ -170,7 +192,7 @@ promotes hot pages. If the scan was done cacheline efficiently, it
 adds the PMD entry pointing to the PTE table to the Bloom filter. This
 forms a feedback loop between the eviction and the aging.
 
-Bloom Filters
+Bloom filters
 -------------
 Bloom filters are a space and memory efficient data structure for set
 membership test, i.e., test if an element is not in the set or may be
@@ -186,6 +208,18 @@ is false positive, the cost is an additional scan of a range of PTEs,
 which may yield hot pages anyway. Parameters of the filter itself can
 control the false positive rate in the limit.
 
+PID controller
+--------------
+A feedback loop modeled after the Proportional-Integral-Derivative
+(PID) controller monitors refaults over anon and file types and
+decides which type to evict when both types are available from the
+same generation.
+
+The PID controller uses generations rather than the wall clock as the
+time domain because a CPU can scan pages at different rates under
+varying memory pressure. It calculates a moving average for each new
+generation to avoid being permanently locked in a suboptimal state.
+
 Memcg LRU
 ---------
 An memcg LRU is a per-node LRU of memcgs. It is also an LRU of LRUs,
@@ -223,9 +257,9 @@ parts:
 
 * Generations
 * Rmap walks
-* Page table walks
-* Bloom filters
-* PID controller
+* Page table walks via ``mm_struct`` list
+* Bloom filters for rmap/PT walk feedback
+* PID controller for refault feedback
 
 The aging and the eviction form a producer-consumer model;
 specifically, the latter drives the former by the sliding window over

Documentation/mm/unevictable-lru.rst

@@ -42,6 +42,8 @@ The unevictable list addresses the following classes of unevictable pages:
 
  * Those owned by ramfs.
 
+ * Those owned by tmpfs with the noswap mount option.
+
  * Those mapped into SHM_LOCK'd shared memory regions.
 
  * Those mapped into VM_LOCKED [mlock()ed] VMAs.

MAINTAINERS

@@ -13457,13 +13457,14 @@ F:	arch/powerpc/include/asm/membarrier.h
 F:	include/uapi/linux/membarrier.h
 F:	kernel/sched/membarrier.c
 
-MEMBLOCK
+MEMBLOCK AND MEMORY MANAGEMENT INITIALIZATION
 M:	Mike Rapoport <rppt@kernel.org>
 L:	linux-mm@kvack.org
 S:	Maintained
 F:	Documentation/core-api/boot-time-mm.rst
 F:	include/linux/memblock.h
 F:	mm/memblock.c
+F:	mm/mm_init.c
 F:	tools/testing/memblock/
 
 MEMORY CONTROLLER DRIVERS
@@ -13498,6 +13499,7 @@ F:	include/linux/memory_hotplug.h
 F:	include/linux/mm.h
 F:	include/linux/mmzone.h
 F:	include/linux/pagewalk.h
+F:	include/trace/events/ksm.h
 F:	mm/
 F:	tools/mm/
 F:	tools/testing/selftests/mm/
@@ -13506,6 +13508,7 @@ VMALLOC
 M:	Andrew Morton <akpm@linux-foundation.org>
 R:	Uladzislau Rezki <urezki@gmail.com>
 R:	Christoph Hellwig <hch@infradead.org>
+R:	Lorenzo Stoakes <lstoakes@gmail.com>
 L:	linux-mm@kvack.org
 S:	Maintained
 W:	http://www.linux-mm.org

arch/Kconfig

@@ -465,6 +465,38 @@ config ARCH_WANT_IRQS_OFF_ACTIVATE_MM
 	  irqs disabled over activate_mm. Architectures that do IPI based TLB
 	  shootdowns should enable this.
 
+# Use normal mm refcounting for MMU_LAZY_TLB kernel thread references.
+# MMU_LAZY_TLB_REFCOUNT=n can improve the scalability of context switching
+# to/from kernel threads when the same mm is running on a lot of CPUs (a large
+# multi-threaded application), by reducing contention on the mm refcount.
+#
+# This can be disabled if the architecture ensures no CPUs are using an mm as a
+# "lazy tlb" beyond its final refcount (i.e., by the time __mmdrop frees the mm
+# or its kernel page tables). This could be arranged by arch_exit_mmap(), or
+# final exit(2) TLB flush, for example.
+#
+# To implement this, an arch *must*:
+# Ensure the _lazy_tlb variants of mmgrab/mmdrop are used when manipulating
+# the lazy tlb reference of a kthread's ->active_mm (non-arch code has been
+# converted already).
+config MMU_LAZY_TLB_REFCOUNT
+	def_bool y
+	depends on !MMU_LAZY_TLB_SHOOTDOWN
+
+# This option allows MMU_LAZY_TLB_REFCOUNT=n. It ensures no CPUs are using an
+# mm as a lazy tlb beyond its last reference count, by shooting down these
+# users before the mm is deallocated. __mmdrop() first IPIs all CPUs that may
+# be using the mm as a lazy tlb, so that they may switch themselves to using
+# init_mm for their active mm. mm_cpumask(mm) is used to determine which CPUs
+# may be using mm as a lazy tlb mm.
+#
+# To implement this, an arch *must*:
+# - At the time of the final mmdrop of the mm, ensure mm_cpumask(mm) contains
+#   at least all possible CPUs in which the mm is lazy.
+# - It must meet the requirements for MMU_LAZY_TLB_REFCOUNT=n (see above).
+config MMU_LAZY_TLB_SHOOTDOWN
+	bool
+
 config ARCH_HAVE_NMI_SAFE_CMPXCHG
 	bool
 

arch/arc/Kconfig

@@ -556,7 +556,7 @@ endmenu	 # "ARC Architecture Configuration"
 
 config ARCH_FORCE_MAX_ORDER
 	int "Maximum zone order"
-	default "12" if ARC_HUGEPAGE_16M
-	default "11"
+	default "11" if ARC_HUGEPAGE_16M
+	default "10"
 
 source "kernel/power/Kconfig"

arch/arc/mm/init.c

@@ -74,11 +74,6 @@ void __init early_init_dt_add_memory_arch(u64 base, u64 size)
 		base, TO_MB(size), !in_use ? "Not used":"");
 }
 
-bool arch_has_descending_max_zone_pfns(void)
-{
-	return !IS_ENABLED(CONFIG_ARC_HAS_PAE40);
-}
-
 /*
  * First memory setup routine called from setup_arch()
  * 1. setup swapper's mm @init_mm

arch/arm/Kconfig

@@ -1352,20 +1352,19 @@ config ARM_MODULE_PLTS
 	  configurations. If unsure, say y.
 
 config ARCH_FORCE_MAX_ORDER
-	int "Maximum zone order"
-	default "12" if SOC_AM33XX
-	default "9" if SA1111
-	default "11"
+	int "Order of maximal physically contiguous allocations"
+	default "11" if SOC_AM33XX
+	default "8" if SA1111
+	default "10"
 	help
-	  The kernel memory allocator divides physically contiguous memory
-	  blocks into "zones", where each zone is a power of two number of
-	  pages.  This option selects the largest power of two that the kernel
-	  keeps in the memory allocator.  If you need to allocate very large
-	  blocks of physically contiguous memory, then you may need to
-	  increase this value.
+	  The kernel page allocator limits the size of maximal physically
+	  contiguous allocations. The limit is called MAX_ORDER and it
+	  defines the maximal power of two of number of pages that can be
+	  allocated as a single contiguous block. This option allows
+	  overriding the default setting when ability to allocate very
+	  large blocks of physically contiguous memory is required.
 
-	  This config option is actually maximum order plus one. For example,
-	  a value of 11 means that the largest free memory block is 2^10 pages.
+	  Don't change if unsure.
 
 config ALIGNMENT_TRAP
 	def_bool CPU_CP15_MMU

arch/arm/configs/imx_v6_v7_defconfig

@@ -31,7 +31,7 @@ CONFIG_SOC_VF610=y
 CONFIG_SMP=y
 CONFIG_ARM_PSCI=y
 CONFIG_HIGHMEM=y
-CONFIG_ARCH_FORCE_MAX_ORDER=14
+CONFIG_ARCH_FORCE_MAX_ORDER=13
 CONFIG_CMDLINE="noinitrd console=ttymxc0,115200"
 CONFIG_KEXEC=y
 CONFIG_CPU_FREQ=y

arch/arm/configs/milbeaut_m10v_defconfig

@@ -26,7 +26,7 @@ CONFIG_THUMB2_KERNEL=y
 # CONFIG_THUMB2_AVOID_R_ARM_THM_JUMP11 is not set
 # CONFIG_ARM_PATCH_IDIV is not set
 CONFIG_HIGHMEM=y
-CONFIG_ARCH_FORCE_MAX_ORDER=12
+CONFIG_ARCH_FORCE_MAX_ORDER=11
 CONFIG_SECCOMP=y
 CONFIG_KEXEC=y
 CONFIG_EFI=y