linux-toradex.git/Documentation/admin-guide/mm, branch v6.7

Merge tag 'mm-stable-2023-11-01-14-33' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

2023-11-03T05:38:47+00:00

Pull MM updates from Andrew Morton:
 "Many singleton patches against the MM code. The patch series which are
  included in this merge do the following:

   - Kemeng Shi has contributed some compation maintenance work in the
     series 'Fixes and cleanups to compaction'

   - Joel Fernandes has a patchset ('Optimize mremap during mutual
     alignment within PMD') which fixes an obscure issue with mremap()'s
     pagetable handling during a subsequent exec(), based upon an
     implementation which Linus suggested

   - More DAMON/DAMOS maintenance and feature work from SeongJae Park i
     the following patch series:

	mm/damon: misc fixups for documents, comments and its tracepoint
	mm/damon: add a tracepoint for damos apply target regions
	mm/damon: provide pseudo-moving sum based access rate
	mm/damon: implement DAMOS apply intervals
	mm/damon/core-test: Fix memory leaks in core-test
	mm/damon/sysfs-schemes: Do DAMOS tried regions update for only one apply interval

   - In the series 'Do not try to access unaccepted memory' Adrian
     Hunter provides some fixups for the recently-added 'unaccepted
     memory' feature. To increase the feature's checking coverage. 'Plug
     a few gaps where RAM is exposed without checking if it is
     unaccepted memory'

   - In the series 'cleanups for lockless slab shrink' Qi Zheng has done
     some maintenance work which is preparation for the lockless slab
     shrinking code

   - Qi Zheng has redone the earlier (and reverted) attempt to make slab
     shrinking lockless in the series 'use refcount+RCU method to
     implement lockless slab shrink'

   - David Hildenbrand contributes some maintenance work for the rmap
     code in the series 'Anon rmap cleanups'

   - Kefeng Wang does more folio conversions and some maintenance work
     in the migration code. Series 'mm: migrate: more folio conversion
     and unification'

   - Matthew Wilcox has fixed an issue in the buffer_head code which was
     causing long stalls under some heavy memory/IO loads. Some cleanups
     were added on the way. Series 'Add and use bdev_getblk()'

   - In the series 'Use nth_page() in place of direct struct page
     manipulation' Zi Yan has fixed a potential issue with the direct
     manipulation of hugetlb page frames

   - In the series 'mm: hugetlb: Skip initialization of gigantic tail
     struct pages if freed by HVO' has improved our handling of gigantic
     pages in the hugetlb vmmemmep optimizaton code. This provides
     significant boot time improvements when significant amounts of
     gigantic pages are in use

   - Matthew Wilcox has sent the series 'Small hugetlb cleanups' - code
     rationalization and folio conversions in the hugetlb code

   - Yin Fengwei has improved mlock()'s handling of large folios in the
     series 'support large folio for mlock'

   - In the series 'Expose swapcache stat for memcg v1' Liu Shixin has
     added statistics for memcg v1 users which are available (and
     useful) under memcg v2

   - Florent Revest has enhanced the MDWE (Memory-Deny-Write-Executable)
     prctl so that userspace may direct the kernel to not automatically
     propagate the denial to child processes. The series is named 'MDWE
     without inheritance'

   - Kefeng Wang has provided the series 'mm: convert numa balancing
     functions to use a folio' which does what it says

   - In the series 'mm/ksm: add fork-exec support for prctl' Stefan
     Roesch makes is possible for a process to propagate KSM treatment
     across exec()

   - Huang Ying has enhanced memory tiering's calculation of memory
     distances. This is used to permit the dax/kmem driver to use 'high
     bandwidth memory' in addition to Optane Data Center Persistent
     Memory Modules (DCPMM). The series is named 'memory tiering:
     calculate abstract distance based on ACPI HMAT'

   - In the series 'Smart scanning mode for KSM' Stefan Roesch has
     optimized KSM by teaching it to retain and use some historical
     information from previous scans

   - Yosry Ahmed has fixed some inconsistencies in memcg statistics in
     the series 'mm: memcg: fix tracking of pending stats updates
     values'

   - In the series 'Implement IOCTL to get and optionally clear info
     about PTEs' Peter Xu has added an ioctl to /proc//pagemap
     which permits us to atomically read-then-clear page softdirty
     state. This is mainly used by CRIU

   - Hugh Dickins contributed the series 'shmem,tmpfs: general
     maintenance', a bunch of relatively minor maintenance tweaks to
     this code

   - Matthew Wilcox has increased the use of the VMA lock over
     file-backed page faults in the series 'Handle more faults under the
     VMA lock'. Some rationalizations of the fault path became possible
     as a result

   - In the series 'mm/rmap: convert page_move_anon_rmap() to
     folio_move_anon_rmap()' David Hildenbrand has implemented some
     cleanups and folio conversions

   - In the series 'various improvements to the GUP interface' Lorenzo
     Stoakes has simplified and improved the GUP interface with an eye
     to providing groundwork for future improvements

   - Andrey Konovalov has sent along the series 'kasan: assorted fixes
     and improvements' which does those things

   - Some page allocator maintenance work from Kemeng Shi in the series
     'Two minor cleanups to break_down_buddy_pages'

   - In thes series 'New selftest for mm' Breno Leitao has developed
     another MM self test which tickles a race we had between madvise()
     and page faults

   - In the series 'Add folio_end_read' Matthew Wilcox provides cleanups
     and an optimization to the core pagecache code

   - Nhat Pham has added memcg accounting for hugetlb memory in the
     series 'hugetlb memcg accounting'

   - Cleanups and rationalizations to the pagemap code from Lorenzo
     Stoakes, in the series 'Abstract vma_merge() and split_vma()'

   - Audra Mitchell has fixed issues in the procfs page_owner code's new
     timestamping feature which was causing some misbehaviours. In the
     series 'Fix page_owner's use of free timestamps'

   - Lorenzo Stoakes has fixed the handling of new mappings of sealed
     files in the series 'permit write-sealed memfd read-only shared
     mappings'

   - Mike Kravetz has optimized the hugetlb vmemmap optimization in the
     series 'Batch hugetlb vmemmap modification operations'

   - Some buffer_head folio conversions and cleanups from Matthew Wilcox
     in the series 'Finish the create_empty_buffers() transition'

   - As a page allocator performance optimization Huang Ying has added
     automatic tuning to the allocator's per-cpu-pages feature, in the
     series 'mm: PCP high auto-tuning'

   - Roman Gushchin has contributed the patchset 'mm: improve
     performance of accounted kernel memory allocations' which improves
     their performance by ~30% as measured by a micro-benchmark

   - folio conversions from Kefeng Wang in the series 'mm: convert page
     cpupid functions to folios'

   - Some kmemleak fixups in Liu Shixin's series 'Some bugfix about
     kmemleak'

   - Qi Zheng has improved our handling of memoryless nodes by keeping
     them off the allocation fallback list. This is done in the series
     'handle memoryless nodes more appropriately'

   - khugepaged conversions from Vishal Moola in the series 'Some
     khugepaged folio conversions'"

[ bcachefs conflicts with the dynamically allocated shrinkers have been
  resolved as per Stephen Rothwell in

     https://lore.kernel.org/all/20230913093553.4290421e@canb.auug.org.au/

  with help from Qi Zheng.

  The clone3 test filtering conflict was half-arsed by yours truly ]

* tag 'mm-stable-2023-11-01-14-33' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm: (406 commits)
  mm/damon/sysfs: update monitoring target regions for online input commit
  mm/damon/sysfs: remove requested targets when online-commit inputs
  selftests: add a sanity check for zswap
  Documentation: maple_tree: fix word spelling error
  mm/vmalloc: fix the unchecked dereference warning in vread_iter()
  zswap: export compression failure stats
  Documentation: ubsan: drop "the" from article title
  mempolicy: migration attempt to match interleave nodes
  mempolicy: mmap_lock is not needed while migrating folios
  mempolicy: alloc_pages_mpol() for NUMA policy without vma
  mm: add page_rmappable_folio() wrapper
  mempolicy: remove confusing MPOL_MF_LAZY dead code
  mempolicy: mpol_shared_policy_init() without pseudo-vma
  mempolicy trivia: use pgoff_t in shared mempolicy tree
  mempolicy trivia: slightly more consistent naming
  mempolicy trivia: delete those ancient pr_debug()s
  mempolicy: fix migrate_pages(2) syscall return nr_failed
  kernfs: drop shared NUMA mempolicy hooks
  hugetlbfs: drop shared NUMA mempolicy pretence
  mm/damon/sysfs-test: add a unit test for damon_sysfs_set_targets()
  ...

Merge tag 'docs-6.7' of git://git.lwn.net/linux

2023-11-02T03:11:41+00:00

Pull documentation updates from Jonathan Corbet:
 "The number of commits for documentation is not huge this time around,
  but there are some significant changes nonetheless:

   - Some more Spanish-language and Chinese translations

   - The much-discussed documentation of the confidential-computing
     threat model

   - Powerpc and RISCV documentation move under Documentation/arch -
     these complete this particular bit of documentation churn

   - A large traditional-Chinese documentation update

   - A new document on backporting and conflict resolution

   - Some kernel-doc and Sphinx fixes

  Plus the usual smattering of smaller updates and typo fixes"

* tag 'docs-6.7' of git://git.lwn.net/linux: (40 commits)
  scripts/kernel-doc: Fix the regex for matching -Werror flag
  docs: backporting: address feedback
  Documentation: driver-api: pps: Update PPS generator documentation
  speakup: Document USB support
  doc: blk-ioprio: Bring the doc in line with the implementation
  docs: usb: fix reference to nonexistent file in UVC Gadget
  docs: doc-guide: mention 'make refcheckdocs'
  Documentation: fix typo in dynamic-debug howto
  scripts/kernel-doc: match -Werror flag strictly
  Documentation/sphinx: Remove the repeated word "the" in comments.
  docs: sparse: add SPDX-License-Identifier
  docs/zh_CN: Add subsystem-apis Chinese translation
  docs/zh_TW: update contents for zh_TW
  docs: submitting-patches: encourage direct notifications to commenters
  docs: add backporting and conflict resolution document
  docs: move riscv under arch
  docs: update link to powerpc/vmemmap_dedup.rst
  mm/memory-hotplug: fix typo in documentation
  docs: move powerpc under arch
  PCI: Update the devres documentation regarding to pcim_*()
  ...

Docs/admin-guide/mm/damon/usage: update for tried regions update time interval

2023-10-18T21:34:19+00:00

The documentation says DAMOS tried regions update feature of DAMON sysfs
interface is doing the update for one aggregation interval after the
request is made.  Since the introduction of the per-scheme apply interval,
that behavior makes no much sense.  Hence the implementation has changed
to update the regions for each scheme for only its apply interval. 
Further update the document to reflect the real behavior.

Link: https://lkml.kernel.org/r/20231012192256.33556-4-sj@kernel.org
Signed-off-by: SeongJae Park 
Cc: Jonathan Corbet 
Signed-off-by: Andrew Morton

mm/pagemap: add documentation of PAGEMAP_SCAN IOCTL

2023-10-18T21:34:13+00:00

Add some explanation and method to use write-protection and written-to
on memory range.

Link: https://lkml.kernel.org/r/20230821141518.870589-6-usama.anjum@collabora.com
Signed-off-by: Muhammad Usama Anjum 
Cc: Alex Sierra 
Cc: Al Viro 
Cc: Andrei Vagin 
Cc: Axel Rasmussen 
Cc: Christian Brauner 
Cc: Cyrill Gorcunov 
Cc: Dan Williams 
Cc: David Hildenbrand 
Cc: Greg Kroah-Hartman 
Cc: Gustavo A. R. Silva 
Cc: "Liam R. Howlett" 
Cc: Matthew Wilcox 
Cc: Michal Miroslaw 
Cc: Michał Mirosław 
Cc: Mike Rapoport (IBM) 
Cc: Nadav Amit 
Cc: Pasha Tatashin 
Cc: Paul Gofman 
Cc: Peter Xu 
Cc: Shuah Khan 
Cc: Suren Baghdasaryan 
Cc: Vlastimil Babka 
Cc: Yang Shi 
Cc: Yun Zhou 
Signed-off-by: Andrew Morton

userfaultfd: UFFD_FEATURE_WP_ASYNC

2023-10-18T21:34:12+00:00

Patch series "Implement IOCTL to get and optionally clear info about
PTEs", v33.

*Motivation*
The real motivation for adding PAGEMAP_SCAN IOCTL is to emulate Windows
GetWriteWatch() and ResetWriteWatch() syscalls [1].  The GetWriteWatch()
retrieves the addresses of the pages that are written to in a region of
virtual memory.

This syscall is used in Windows applications and games etc.  This syscall
is being emulated in pretty slow manner in userspace.  Our purpose is to
enhance the kernel such that we translate it efficiently in a better way. 
Currently some out of tree hack patches are being used to efficiently
emulate it in some kernels.  We intend to replace those with these
patches.  So the whole gaming on Linux can effectively get benefit from
this.  It means there would be tons of users of this code.

CRIU use case [2] was mentioned by Andrei and Danylo:
> Use cases for migrating sparse VMAs are binaries sanitized with ASAN,
> MSAN or TSAN [3]. All of these sanitizers produce sparse mappings of
> shadow memory [4]. Being able to migrate such binaries allows to highly
> reduce the amount of work needed to identify and fix post-migration
> crashes, which happen constantly.

Andrei defines the following uses of this code:
* it is more granular and allows us to track changed pages more
  effectively. The current interface can clear dirty bits for the entire
  process only. In addition, reading info about pages is a separate
  operation. It means we must freeze the process to read information
  about all its pages, reset dirty bits, only then we can start dumping
  pages. The information about pages becomes more and more outdated,
  while we are processing pages. The new interface solves both these
  downsides. First, it allows us to read pte bits and clear the
  soft-dirty bit atomically. It means that CRIU will not need to freeze
  processes to pre-dump their memory. Second, it clears soft-dirty bits
  for a specified region of memory. It means CRIU will have actual info
  about pages to the moment of dumping them.
* The new interface has to be much faster because basic page filtering
  is happening in the kernel. With the old interface, we have to read
  pagemap for each page.

*Implementation Evolution (Short Summary)*
From the definition of GetWriteWatch(), we feel like kernel's soft-dirty
feature can be used under the hood with some additions like:
* reset soft-dirty flag for only a specific region of memory instead of
clearing the flag for the entire process
* get and clear soft-dirty flag for a specific region atomically

So we decided to use ioctl on pagemap file to read or/and reset soft-dirty
flag. But using soft-dirty flag, sometimes we get extra pages which weren't
even written. They had become soft-dirty because of VMA merging and
VM_SOFTDIRTY flag. This breaks the definition of GetWriteWatch(). We were
able to by-pass this short coming by ignoring VM_SOFTDIRTY until David
reported that mprotect etc messes up the soft-dirty flag while ignoring
VM_SOFTDIRTY [5]. This wasn't happening until [6] got introduced. We
discussed if we can revert these patches. But we could not reach to any
conclusion. So at this point, I made couple of tries to solve this whole
VM_SOFTDIRTY issue by correcting the soft-dirty implementation:
* [7] Correct the bug fixed wrongly back in 2014. It had potential to cause
regression. We left it behind.
* [8] Keep a list of soft-dirty part of a VMA across splits and merges. I
got the reply don't increase the size of the VMA by 8 bytes.

At this point, we left soft-dirty considering it is too much delicate and
userfaultfd [9] seemed like the only way forward. From there onward, we
have been basing soft-dirty emulation on userfaultfd wp feature where
kernel resolves the faults itself when WP_ASYNC feature is used. It was
straight forward to add WP_ASYNC feature in userfautlfd. Now we get only
those pages dirty or written-to which are really written in reality. (PS
There is another WP_UNPOPULATED userfautfd feature is required which is
needed to avoid pre-faulting memory before write-protecting [9].)

All the different masks were added on the request of CRIU devs to create
interface more generic and better.

[1] https://learn.microsoft.com/en-us/windows/win32/api/memoryapi/nf-memoryapi-getwritewatch
[2] https://lore.kernel.org/all/20221014134802.1361436-1-mdanylo@google.com
[3] https://github.com/google/sanitizers
[4] https://github.com/google/sanitizers/wiki/AddressSanitizerAlgorithm#64-bit
[5] https://lore.kernel.org/all/bfcae708-db21-04b4-0bbe-712badd03071@redhat.com
[6] https://lore.kernel.org/all/20220725142048.30450-1-peterx@redhat.com/
[7] https://lore.kernel.org/all/20221122115007.2787017-1-usama.anjum@collabora.com
[8] https://lore.kernel.org/all/20221220162606.1595355-1-usama.anjum@collabora.com
[9] https://lore.kernel.org/all/20230306213925.617814-1-peterx@redhat.com
[10] https://lore.kernel.org/all/20230125144529.1630917-1-mdanylo@google.com


This patch (of 6):

Add a new userfaultfd-wp feature UFFD_FEATURE_WP_ASYNC, that allows
userfaultfd wr-protect faults to be resolved by the kernel directly.

It can be used like a high accuracy version of soft-dirty, without vma
modifications during tracking, and also with ranged support by default
rather than for a whole mm when reset the protections due to existence of
ioctl(UFFDIO_WRITEPROTECT).

Several goals of such a dirty tracking interface:

1. All types of memory should be supported and tracable. This is nature
   for soft-dirty but should mention when the context is userfaultfd,
   because it used to only support anon/shmem/hugetlb. The problem is for
   a dirty tracking purpose these three types may not be enough, and it's
   legal to track anything e.g. any page cache writes from mmap.

2. Protections can be applied to partial of a memory range, without vma
   split/merge fuss.  The hope is that the tracking itself should not
   affect any vma layout change.  It also helps when reset happens because
   the reset will not need mmap write lock which can block the tracee.

3. Accuracy needs to be maintained.  This means we need pte markers to work
   on any type of VMA.

One could question that, the whole concept of async dirty tracking is not
really close to fundamentally what userfaultfd used to be: it's not "a
fault to be serviced by userspace" anymore. However, using userfaultfd-wp
here as a framework is convenient for us in at least:

1. VM_UFFD_WP vma flag, which has a very good name to suite something like
   this, so we don't need VM_YET_ANOTHER_SOFT_DIRTY. Just use a new
   feature bit to identify from a sync version of uffd-wp registration.

2. PTE markers logic can be leveraged across the whole kernel to maintain
   the uffd-wp bit as long as an arch supports, this also applies to this
   case where uffd-wp bit will be a hint to dirty information and it will
   not go lost easily (e.g. when some page cache ptes got zapped).

3. Reuse ioctl(UFFDIO_WRITEPROTECT) interface for either starting or
   resetting a range of memory, while there's no counterpart in the old
   soft-dirty world, hence if this is wanted in a new design we'll need a
   new interface otherwise.

We can somehow understand that commonality because uffd-wp was
fundamentally a similar idea of write-protecting pages just like
soft-dirty.

This implementation allows WP_ASYNC to imply WP_UNPOPULATED, because so
far WP_ASYNC seems to not usable if without WP_UNPOPULATE.  This also
gives us chance to modify impl of WP_ASYNC just in case it could be not
depending on WP_UNPOPULATED anymore in the future kernels.  It's also fine
to imply that because both features will rely on PTE_MARKER_UFFD_WP config
option, so they'll show up together (or both missing) in an UFFDIO_API
probe.

vma_can_userfault() now allows any VMA if the userfaultfd registration is
only about async uffd-wp.  So we can track dirty for all kinds of memory
including generic file systems (like XFS, EXT4 or BTRFS).

One trick worth mention in do_wp_page() is that we need to manually update
vmf->orig_pte here because it can be used later with a pte_same() check -
this path always has FAULT_FLAG_ORIG_PTE_VALID set in the flags.

The major defect of this approach of dirty tracking is we need to populate
the pgtables when tracking starts.  Soft-dirty doesn't do it like that. 
It's unwanted in the case where the range of memory to track is huge and
unpopulated (e.g., tracking updates on a 10G file with mmap() on top,
without having any page cache installed yet).  One way to improve this is
to allow pte markers exist for larger than PTE level for PMD+.  That will
not change the interface if to implemented, so we can leave that for
later.

Link: https://lkml.kernel.org/r/20230821141518.870589-1-usama.anjum@collabora.com
Link: https://lkml.kernel.org/r/20230821141518.870589-2-usama.anjum@collabora.com
Signed-off-by: Peter Xu 
Co-developed-by: Muhammad Usama Anjum 
Signed-off-by: Muhammad Usama Anjum 
Cc: Alex Sierra 
Cc: Al Viro 
Cc: Andrei Vagin 
Cc: Axel Rasmussen 
Cc: Christian Brauner 
Cc: Cyrill Gorcunov 
Cc: Dan Williams 
Cc: David Hildenbrand 
Cc: Greg Kroah-Hartman 
Cc: Gustavo A. R. Silva 
Cc: "Liam R. Howlett" 
Cc: Matthew Wilcox 
Cc: Michal Miroslaw 
Cc: Mike Rapoport (IBM) 
Cc: Nadav Amit 
Cc: Pasha Tatashin 
Cc: Paul Gofman 
Cc: Shuah Khan 
Cc: Suren Baghdasaryan 
Cc: Vlastimil Babka 
Cc: Yang Shi 
Cc: Yun Zhou 
Cc: Michał Mirosław 
Signed-off-by: Andrew Morton

mm/ksm: document pages_skipped sysfs knob

2023-10-16T22:44:39+00:00

This adds documentation for the new metric pages_skipped.

Link: https://lkml.kernel.org/r/20230926040939.516161-5-shr@devkernel.io
Signed-off-by: Stefan Roesch 
Reviewed-by: David Hildenbrand 
Cc: Johannes Weiner 
Cc: Rik van Riel 
Signed-off-by: Andrew Morton

mm/ksm: document smart scan mode

2023-10-16T22:44:39+00:00

This adds documentation for the smart scan mode of KSM.

[akpm@linux-foundation.org: fix typo]
[akpm@linux-foundation.org: document that smart_scan defaults to on]
Link: https://lkml.kernel.org/r/20230926040939.516161-4-shr@devkernel.io
Signed-off-by: Stefan Roesch 
Reviewed-by: David Hildenbrand 
Cc: Johannes Weiner 
Cc: Rik van Riel 
Signed-off-by: Andrew Morton

mm/memory-hotplug: fix typo in documentation

2023-10-10T19:35:55+00:00

I'm 90% sure memory hotunplugging doesn't involve a "fist" phase

Signed-off-by: Amos Wenger 
Reviewed-by: David Hildenbrand 
Signed-off-by: Jonathan Corbet 
Link: https://lore.kernel.org/r/20231006112636.97128-1-amos@bearcove.net

Docs/admin-guide/mm/damon/usage: update for DAMOS apply intervals

2023-10-04T17:32:31+00:00

Update DAMON usage document's DAMON sysfs interface section for the newly
added DAMOS apply intervals support (apply_interval_us file).

Link: https://lkml.kernel.org/r/20230916020945.47296-9-sj@kernel.org
Signed-off-by: SeongJae Park 
Cc: Jonathan Corbet 
Cc: Shuah Khan 
Cc: Steven Rostedt (Google) 
Signed-off-by: Andrew Morton

Docs/admin-guide/mm/damon/usage: document damos_before_apply tracepoint

2023-10-04T17:32:28+00:00

Document damos_before_apply tracepoint on the usage document.

Link: https://lkml.kernel.org/r/20230913022050.2109-3-sj@kernel.org
Signed-off-by: SeongJae Park 
Cc: Jonathan Corbet 
Cc: Steven Rostedt (Google) 
Signed-off-by: Andrew Morton