Merge tag 'mm-stable-2022-10-08' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

Pull MM updates from Andrew Morton:

 - Yu Zhao's Multi-Gen LRU patches are here. They've been under test in
   linux-next for a couple of months without, to my knowledge, any
   negative reports (or any positive ones, come to that).

 - Also the Maple Tree from Liam Howlett. An overlapping range-based
   tree for vmas. It it apparently slightly more efficient in its own
   right, but is mainly targeted at enabling work to reduce mmap_lock
   contention.

   Liam has identified a number of other tree users in the kernel which
   could be beneficially onverted to mapletrees.

   Yu Zhao has identified a hard-to-hit but "easy to fix" lockdep splat
   at [1]. This has yet to be addressed due to Liam's unfortunately
   timed vacation. He is now back and we'll get this fixed up.

 - Dmitry Vyukov introduces KMSAN: the Kernel Memory Sanitizer. It uses
   clang-generated instrumentation to detect used-unintialized bugs down
   to the single bit level.

   KMSAN keeps finding bugs. New ones, as well as the legacy ones.

 - Yang Shi adds a userspace mechanism (madvise) to induce a collapse of
   memory into THPs.

 - Zach O'Keefe has expanded Yang Shi's madvise(MADV_COLLAPSE) to
   support file/shmem-backed pages.

 - userfaultfd updates from Axel Rasmussen

 - zsmalloc cleanups from Alexey Romanov

 - cleanups from Miaohe Lin: vmscan, hugetlb_cgroup, hugetlb and
   memory-failure

 - Huang Ying adds enhancements to NUMA balancing memory tiering mode's
   page promotion, with a new way of detecting hot pages.

 - memcg updates from Shakeel Butt: charging optimizations and reduced
   memory consumption.

 - memcg cleanups from Kairui Song.

 - memcg fixes and cleanups from Johannes Weiner.

 - Vishal Moola provides more folio conversions

 - Zhang Yi removed ll_rw_block() :(

 - migration enhancements from Peter Xu

 - migration error-path bugfixes from Huang Ying

 - Aneesh Kumar added ability for a device driver to alter the memory
   tiering promotion paths. For optimizations by PMEM drivers, DRM
   drivers, etc.

 - vma merging improvements from Jakub Matěn.

 - NUMA hinting cleanups from David Hildenbrand.

 - xu xin added aditional userspace visibility into KSM merging
   activity.

 - THP & KSM code consolidation from Qi Zheng.

 - more folio work from Matthew Wilcox.

 - KASAN updates from Andrey Konovalov.

 - DAMON cleanups from Kaixu Xia.

 - DAMON work from SeongJae Park: fixes, cleanups.

 - hugetlb sysfs cleanups from Muchun Song.

 - Mike Kravetz fixes locking issues in hugetlbfs and in hugetlb core.

Link: https://lkml.kernel.org/r/CAOUHufZabH85CeUN-MEMgL8gJGzJEWUrkiM58JkTbBhh-jew0Q@mail.gmail.com [1]

* tag 'mm-stable-2022-10-08' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm: (555 commits)
  hugetlb: allocate vma lock for all sharable vmas
  hugetlb: take hugetlb vma_lock when clearing vma_lock->vma pointer
  hugetlb: fix vma lock handling during split vma and range unmapping
  mglru: mm/vmscan.c: fix imprecise comments
  mm/mglru: don't sync disk for each aging cycle
  mm: memcontrol: drop dead CONFIG_MEMCG_SWAP config symbol
  mm: memcontrol: use do_memsw_account() in a few more places
  mm: memcontrol: deprecate swapaccounting=0 mode
  mm: memcontrol: don't allocate cgroup swap arrays when memcg is disabled
  mm/secretmem: remove reduntant return value
  mm/hugetlb: add available_huge_pages() func
  mm: remove unused inline functions from include/linux/mm_inline.h
  selftests/vm: add selftest for MADV_COLLAPSE of uffd-minor memory
  selftests/vm: add file/shmem MADV_COLLAPSE selftest for cleared pmd
  selftests/vm: add thp collapse shmem testing
  selftests/vm: add thp collapse file and tmpfs testing
  selftests/vm: modularize thp collapse memory operations
  selftests/vm: dedup THP helpers
  mm/khugepaged: add tracepoint to hpage_collapse_scan_file()
  mm/madvise: add file and shmem support to MADV_COLLAPSE
  ...

4 files changed, 166 insertions, 1 deletions

diff --git a/Documentation/mm/index.rst b/Documentation/mm/index.rst
index 575ccd40e30c..4aa12b8be278 100644
--- a/Documentation/mm/index.rst
+++ b/Documentation/mm/index.rst
@@ -51,6 +51,7 @@ above structured documentation, or deleted if it has served its purpose.
    ksm
    memory-model
    mmu_notifier
+   multigen_lru
    numa
    overcommit-accounting
    page_migration
diff --git a/Documentation/mm/ksm.rst b/Documentation/mm/ksm.rst
index 9e37add068e6..f83cfbc12f4c 100644
--- a/Documentation/mm/ksm.rst
+++ b/Documentation/mm/ksm.rst
@@ -26,7 +26,7 @@ tree.
 
 If a KSM page is shared between less than ``max_page_sharing`` VMAs,
 the node of the stable tree that represents such KSM page points to a
-list of struct rmap_item and the ``page->mapping`` of the
+list of struct ksm_rmap_item and the ``page->mapping`` of the
 KSM page points to the stable tree node.
 
 When the sharing passes this threshold, KSM adds a second dimension to
diff --git a/Documentation/mm/multigen_lru.rst b/Documentation/mm/multigen_lru.rst
new file mode 100644
index 000000000000..d7062c6a8946
--- /dev/null
+++ b/Documentation/mm/multigen_lru.rst
@@ -0,0 +1,159 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+=============
+Multi-Gen LRU
+=============
+The multi-gen LRU is an alternative LRU implementation that optimizes
+page reclaim and improves performance under memory pressure. Page
+reclaim decides the kernel's caching policy and ability to overcommit
+memory. It directly impacts the kswapd CPU usage and RAM efficiency.
+
+Design overview
+===============
+Objectives
+----------
+The design objectives are:
+
+* Good representation of access recency
+* Try to profit from spatial locality
+* Fast paths to make obvious choices
+* Simple self-correcting heuristics
+
+The representation of access recency is at the core of all LRU
+implementations. In the multi-gen LRU, each generation represents a
+group of pages with similar access recency. Generations establish a
+(time-based) common frame of reference and therefore help make better
+choices, e.g., between different memcgs on a computer or different
+computers in a data center (for job scheduling).
+
+Exploiting spatial locality improves efficiency when gathering the
+accessed bit. A rmap walk targets a single page and does not try to
+profit from discovering a young PTE. A page table walk can sweep all
+the young PTEs in an address space, but the address space can be too
+sparse to make a profit. The key is to optimize both methods and use
+them in combination.
+
+Fast paths reduce code complexity and runtime overhead. Unmapped pages
+do not require TLB flushes; clean pages do not require writeback.
+These facts are only helpful when other conditions, e.g., access
+recency, are similar. With generations as a common frame of reference,
+additional factors stand out. But obvious choices might not be good
+choices; thus self-correction is necessary.
+
+The benefits of simple self-correcting heuristics are self-evident.
+Again, with generations as a common frame of reference, this becomes
+attainable. Specifically, pages in the same generation can be
+categorized based on additional factors, and a feedback loop can
+statistically compare the refault percentages across those categories
+and infer which of them are better choices.
+
+Assumptions
+-----------
+The protection of hot pages and the selection of cold pages are based
+on page access channels and patterns. There are two access channels:
+
+* Accesses through page tables
+* Accesses through file descriptors
+
+The protection of the former channel is by design stronger because:
+
+1. The uncertainty in determining the access patterns of the former
+   channel is higher due to the approximation of the accessed bit.
+2. The cost of evicting the former channel is higher due to the TLB
+   flushes required and the likelihood of encountering the dirty bit.
+3. The penalty of underprotecting the former channel is higher because
+   applications usually do not prepare themselves for major page
+   faults like they do for blocked I/O. E.g., GUI applications
+   commonly use dedicated I/O threads to avoid blocking rendering
+   threads.
+
+There are also two access patterns:
+
+* Accesses exhibiting temporal locality
+* Accesses not exhibiting temporal locality
+
+For the reasons listed above, the former channel is assumed to follow
+the former pattern unless ``VM_SEQ_READ`` or ``VM_RAND_READ`` is
+present, and the latter channel is assumed to follow the latter
+pattern unless outlying refaults have been observed.
+
+Workflow overview
+=================
+Evictable pages are divided into multiple generations for each
+``lruvec``. The youngest generation number is stored in
+``lrugen->max_seq`` for both anon and file types as they are aged on
+an equal footing. The oldest generation numbers are stored in
+``lrugen->min_seq[]`` separately for anon and file types as clean file
+pages can be evicted regardless of swap constraints. These three
+variables are monotonically increasing.
+
+Generation numbers are truncated into ``order_base_2(MAX_NR_GENS+1)``
+bits in order to fit into the gen counter in ``folio->flags``. Each
+truncated generation number is an index to ``lrugen->lists[]``. The
+sliding window technique is used to track at least ``MIN_NR_GENS`` and
+at most ``MAX_NR_GENS`` generations. The gen counter stores a value
+within ``[1, MAX_NR_GENS]`` while a page is on one of
+``lrugen->lists[]``; otherwise it stores zero.
+
+Each generation is divided into multiple tiers. A page accessed ``N``
+times through file descriptors is in tier ``order_base_2(N)``. Unlike
+generations, tiers do not have dedicated ``lrugen->lists[]``. In
+contrast to moving across generations, which requires the LRU lock,
+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.
+
+There are two conceptually independent procedures: the aging and the
+eviction. They form a closed-loop system, i.e., the page reclaim.
+
+Aging
+-----
+The aging produces young generations. Given an ``lruvec``, it
+increments ``max_seq`` when ``max_seq-min_seq+1`` approaches
+``MIN_NR_GENS``. The aging promotes hot pages to the youngest
+generation when it finds them accessed through page tables; the
+demotion of cold pages happens consequently when it increments
+``max_seq``. The aging uses page table walks and rmap walks to find
+young PTEs. For the former, it iterates ``lruvec_memcg()->mm_list``
+and calls ``walk_page_range()`` with each ``mm_struct`` on this list
+to scan PTEs, and after each iteration, it increments ``max_seq``. For
+the latter, when the eviction walks the rmap and finds a young PTE,
+the aging scans the adjacent PTEs. For both, on finding a young PTE,
+the aging clears the accessed bit and updates the gen counter of the
+page mapped by this PTE to ``(max_seq%MAX_NR_GENS)+1``.
+
+Eviction
+--------
+The eviction consumes old generations. Given an ``lruvec``, it
+increments ``min_seq`` when ``lrugen->lists[]`` indexed by
+``min_seq%MAX_NR_GENS`` becomes empty. To select a type and a tier to
+evict from, it first compares ``min_seq[]`` to select the older type.
+If both types are equally old, it selects the one whose first tier has
+a lower refault percentage. The first tier contains single-use
+unmapped clean pages, which are the best bet. The eviction sorts a
+page according to its gen counter if the aging has found this page
+accessed through page tables and updated its gen counter. It also
+moves a page to the next generation, i.e., ``min_seq+1``, if this page
+was accessed multiple times through file descriptors and the feedback
+loop has detected outlying refaults from the tier this page is in. To
+this end, the feedback loop uses the first tier as the baseline, for
+the reason stated earlier.
+
+Summary
+-------
+The multi-gen LRU can be disassembled into the following parts:
+
+* Generations
+* Rmap walks
+* Page table walks
+* Bloom filters
+* PID controller
+
+The aging and the eviction form a producer-consumer model;
+specifically, the latter drives the former by the sliding window over
+generations. Within the aging, rmap walks drive page table walks by
+inserting hot densely populated page tables to the Bloom filters.
+Within the eviction, the PID controller uses refaults as the feedback
+to select types to evict and tiers to protect.
diff --git a/Documentation/mm/page_owner.rst b/Documentation/mm/page_owner.rst
index f5c954afe97c..f18fd8907049 100644
--- a/Documentation/mm/page_owner.rst
+++ b/Documentation/mm/page_owner.rst
@@ -94,6 +94,11 @@ Usage
 	Page allocated via order XXX, ...
 	PFN XXX ...
 	// Detailed stack
+    By default, it will do full pfn dump, to start with a given pfn,
+    page_owner supports fseek.
+
+    FILE *fp = fopen("/sys/kernel/debug/page_owner", "r");
+    fseek(fp, pfn_start, SEEK_SET);
 
    The ``page_owner_sort`` tool ignores ``PFN`` rows, puts the remaining rows
    in buf, uses regexp to extract the page order value, counts the times