kernel/linux.git/Documentation/mm, branch v6.18.33

Documentation: fix a hugetlbfs reservation statement

2026-05-23T11:06:41+00:00

[ Upstream commit 7a197d346a44384a1a858a98ef03766840e561d4 ] Documentation/mm/hugetlbfs_reserv.rst has if (resv_needed <= (resv_huge_pages - free_huge_pages)) resv_huge_pages += resv_needed; which describes this code in gather_surplus_pages() needed = (h->resv_huge_pages + delta) - h->free_huge_pages; if (needed <= 0) { h->resv_huge_pages += delta; return 0; } which means if there are enough free hugepages to account for the new reservation, simply update the global reservation count without further action. But the description is backwards, it should be if (resv_needed <= (free_huge_pages - resv_huge_pages)) instead. Link: https://lkml.kernel.org/r/20260302201015.1824798-1-jane.chu@oracle.com Fixes: 70bc0dc578b3 ("Documentation: vm, add hugetlbfs reservation overview") Signed-off-by: Jane Chu Cc: David Hildenbrand Cc: Hillf Danton Cc: Jonathan Corbet Cc: Liam Howlett Cc: Lorenzo Stoakes Cc: Michal Hocko Cc: Mike Rapoport Cc: Muchun Song Cc: Oscar Salvador Cc: Shuah Khan Cc: Suren Baghdasaryan Cc: Vlastimil Babka Signed-off-by: Andrew Morton Signed-off-by: Sasha Levin

Merge tag 'mm-stable-2025-10-03-16-49' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

2025-10-05T19:11:07+00:00

Pull more MM updates from Andrew Morton: "Only two patch series in this pull request: - "mm/memory_hotplug: fixup crash during uevent handling" from Hannes Reinecke fixes a race that was causing udev to trigger a crash in the memory hotplug code - "mm_slot: following fixup for usage of mm_slot_entry()" from Wei Yang adds some touchups to the just-merged mm_slot changes" * tag 'mm-stable-2025-10-03-16-49' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm: mm/khugepaged: use KMEM_CACHE() mm/ksm: cleanup mm_slot_entry() invocation Documentation/mm: drop pxx_mkdevmap() descriptions from page table helpers mm: clean up is_guard_pte_marker() drivers/base: move memory_block_add_nid() into the caller mm/memory_hotplug: activate node before adding new memory blocks drivers/base/memory: add node id parameter to add_memory_block()

Merge tag 'docs-6.18' of git://git.lwn.net/linux

2025-10-04T00:16:13+00:00

Pull documentation updates from Jonathan Corbet: "It has been a relatively busy cycle in docsland, with changes all over: - Bring the kernel memory-model docs into the Sphinx build in the "literal include" mode. - Lots of build-infrastructure work, further cleaning up long-term kernel-doc technical debt. The sphinx-pre-install tool has been converted to Python and updated for current systems. - A new tool to detect when documents have been moved and generate HTML redirects; this can be used on kernel.org (or any other site hosting the rendered docs) to avoid breaking links. - Automated processing of the YAML files describing the netlink protocol. - A significant update of the maintainer's PGP guide. ... and a seemingly endless series of typo fixes, build-problem fixes, etc" * tag 'docs-6.18' of git://git.lwn.net/linux: (193 commits) Documentation/features: Update feature lists for 6.17-rc7 docs: remove cdomain.py Documentation/process: submitting-patches: fix typo in "were do" docs: dev-tools/lkmm: Fix typo of missing file extension Documentation: trace: histogram: Convert ftrace docs cross-reference Documentation: trace: histogram-design: Wrap introductory note in note:: directive Documentation: trace: historgram-design: Separate sched_waking histogram section heading and the following diagram Documentation: trace: histogram-design: Trim trailing vertices in diagram explanation text Documentation: trace: histogram: Fix histogram trigger subsection number order docs: driver-api: fix spelling of "buses". Documentation: fbcon: Use admonition directives Documentation: fbcon: Reindent 8th step of attach/detach/unload Documentation: fbcon: Add boot options and attach/detach/unload section headings docs: filesystems: sysfs: add remaining top level sysfs directory descriptions docs: filesystems: sysfs: clarify symlink destinations in dev and bus/devices descriptions docs: filesystems: sysfs: remove top level sysfs net directory docs: maintainer: Fix ambiguous subheading formatting docs: kdoc: a few more dump_typedef() tweaks docs: kdoc: remove redundant comment stripping in dump_typedef() docs: kdoc: remove some dead code in dump_typedef() ...

Documentation/mm: drop pxx_mkdevmap() descriptions from page table helpers

2025-10-03T23:42:44+00:00

Remove pxx_mkdevmap() descriptions, as these helper functions have already been dropped (including DEBUG_VM_PGTABLE test) via the commit d438d2734170 ("mm: remove devmap related functions and page table bits"). Link: https://lkml.kernel.org/r/20250929120045.1109707-1-anshuman.khandual@arm.com Signed-off-by: Anshuman Khandual Acked-by: David Hildenbrand Reviewed-by: Dev Jain Cc: Lorenzo Stoakes Cc: Alistair Popple Signed-off-by: Andrew Morton

Docs/mm/damon/maintainer-profile: update community meetup for reservation requirements

2025-09-21T21:22:36+00:00

DAMON community meetup was having two different kinds of meetups: reservation required ones and unrequired ones. Now the reservation unrequested one is gone, but the documentation on the maintainer-profile is not updated. Update. Link: https://lkml.kernel.org/r/20250916032339.115817-4-sj@kernel.org Signed-off-by: SeongJae Park Reviewed-by: Joshua Hahn Cc: David Hildenbrand Cc: Jonathan Corbet Cc: Liam Howlett Cc: Lorenzo Stoakes Cc: Michal Hocko Cc: Mike Rapoport Cc: Suren Baghdasaryan Cc: Vlastimil Babka Signed-off-by: Andrew Morton

docs/mm: add document for swap table

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

Patch series "mm, swap: introduce swap table as swap cache (phase I)", v4. This is the first phase of the bigger series implementing basic infrastructures for the Swap Table idea proposed at the LSF/MM/BPF topic "Integrate swap cache, swap maps with swap allocator" [1]. To give credit where it is due, this is based on Chris Li's idea and a prototype of using cluster size atomic arrays to implement swap cache. This phase I contains 15 patches, introduces the swap table infrastructure and uses it as the swap cache backend. By doing so, we have up to ~5-20% performance gain in throughput, RPS or build time for benchmark and workload tests. The speed up is due to less contention on the swap cache access and shallower swap cache lookup path. The cluster size is much finer-grained than the 64M address space split, which is removed in this phase I. It also unifies and cleans up the swap code base. Each swap cluster will dynamically allocate the swap table, which is an atomic array to cover every swap slot in the cluster. It replaces the swap cache backed by XArray. In phase I, the static allocated swap_map still co-exists with the swap table. The memory usage is about the same as the original on average. A few exception test cases show about 1% higher in memory usage. In the following phases of the series, swap_map will merge into the swap table without additional memory allocation. It will result in net memory reduction compared to the original swap cache. Testing has shown that phase I has a significant performance improvement from 8c/1G ARM machine to 48c96t/128G x86_64 servers in many practical workloads. The full picture with a summary can be found at [2]. An older bigger series of 28 patches is posted at [3]. vm-scability test: ================== Test with: usemem --init-time -O -y -x -n 31 1G (4G memcg, PMEM as swap) Before: After: System time: 219.12s 158.16s (-27.82%) Sum Throughput: 4767.13 MB/s 6128.59 MB/s (+28.55%) Single process Throughput: 150.21 MB/s 196.52 MB/s (+30.83%) Free latency: 175047.58 us 131411.87 us (-24.92%) usemem --init-time -O -y -x -n 32 1536M (16G memory, global pressure, PMEM as swap) Before: After: System time: 356.16s 284.68s (-20.06%) Sum Throughput: 4648.35 MB/s 5453.52 MB/s (+17.32%) Single process Throughput: 141.63 MB/s 168.35 MB/s (+18.86%) Free latency: 499907.71 us 484977.03 us (-2.99%) This shows an improvement of more than 20% improvement in most readings. Build kernel test: ================== The following result matrix is from building kernel with defconfig on tmpfs with ZSWAP / ZRAM, using different memory pressure and setups. Measuring sys and real time in seconds, less is better (user time is almost identical as expected): -j / Mem | Sys before / after | Real before / after Using 16G ZRAM with memcg limit: 6 / 192M | 9686 / 9472 -2.21% | 2130 / 2096 -1.59% 12 / 256M | 6610 / 6451 -2.41% | 827 / 812 -1.81% 24 / 384M | 5938 / 5701 -3.37% | 414 / 405 -2.17% 48 / 768M | 4696 / 4409 -6.11% | 188 / 182 -3.19% With 64k folio: 24 / 512M | 4222 / 4162 -1.42% | 326 / 321 -1.53% 48 / 1G | 3688 / 3622 -1.79% | 151 / 149 -1.32% With ZSWAP with 3G memcg (using higher limit due to kmem account): 48 / 3G | 603 / 581 -3.65% | 81 / 80 -1.23% Testing extremely high global memory and schedule pressure: Using ZSWAP with 32G NVMEs in a 48c VM that has 4G memory, no memcg limit, system components take up about 1.5G already, using make -j48 to build defconfig: Before: sys time: 2069.53s real time: 135.76s After: sys time: 2021.13s (-2.34%) real time: 134.23s (-1.12%) On another 48c 4G memory VM, using 16G ZRAM as swap, testing make -j48 with same config: Before: sys time: 1756.96s real time: 111.01s After: sys time: 1715.90s (-2.34%) real time: 109.51s (-1.35%) All cases are more or less faster, and no regression even under extremely heavy global memory pressure. Redis / Valkey bench: ===================== The test machine is a ARM64 VM with 1536M memory 12 cores, Redis is set to use 2500M memory, and ZRAM swap size is set to 5G: Testing with: redis-benchmark -r 2000000 -n 2000000 -d 1024 -c 12 -P 32 -t get no BGSAVE with BGSAVE Before: 487576.06 RPS 280016.02 RPS After: 487541.76 RPS (-0.01%) 300155.32 RPS (+7.19%) Testing with: redis-benchmark -r 2500000 -n 2500000 -d 1024 -c 12 -P 32 -t get no BGSAVE with BGSAVE Before: 466789.59 RPS 281213.92 RPS After: 466402.89 RPS (-0.08%) 298411.84 RPS (+6.12%) With BGSAVE enabled, most Redis memory will have a swap count > 1 so swap cache is heavily in use. We can see a about 6% performance gain. No BGSAVE is very slightly slower (<0.1%) due to the higher memory pressure of the co-existence of swap_map and swap table. This will be optimzed into a net gain and up to 20% gain in BGSAVE case in the following phases. HDD swap is also ~40% faster with usemem because we removed an old contention workaround. This patch (of 15): Swap table is the new swap cache. [chrisl@kernel.org: move swap table document, redo swap table size sentence] Link: https://lkml.kernel.org/r/CACePvbXjaUyzB_9RSSSgR6BNvz+L9anvn0vcNf_J0jD7-4Yy6Q@mail.gmail.com Link: https://lkml.kernel.org/r/20250916160100.31545-1-ryncsn@gmail.com Link: https://lore.kernel.org/linux-mm/20250514201729.48420-1-ryncsn@gmail.com/ [3] Link: https://lkml.kernel.org/r/20250916160100.31545-2-ryncsn@gmail.com Link: https://lore.kernel.org/CAMgjq7BvQ0ZXvyLGp2YP96+i+6COCBBJCYmjXHGBnfisCAb8VA@mail.gmail.com [1] Link: https://github.com/ryncsn/linux/tree/kasong/devel/swap-table [2] Signed-off-by: Chris Li Signed-off-by: Kairui Song Suggested-by: Chris Li Cc: Baolin Wang Cc: Baoquan He Cc: Barry Song Cc: David Hildenbrand Cc: "Huang, Ying" Cc: Hugh Dickins Cc: Johannes Weiner Cc: Kemeng Shi Cc: Lorenzo Stoakes Cc: Matthew Wilcox (Oracle) Cc: Nhat Pham Cc: Yosry Ahmed Cc: Zi Yan Cc: kernel test robot Cc: SeongJae Park Signed-off-by: Andrew Morton

Docs/admin-guide/mm/damon/usage: document addr_unit file

2025-09-13T23:55:23+00:00

Document addr_unit DAMON sysfs file on DAMON usage document. Link: https://lkml.kernel.org/r/20250828171242.59810-10-sj@kernel.org Signed-off-by: SeongJae Park Signed-off-by: Quanmin Yan Reviewed-by: SeongJae Park Cc: David Hildenbrand Cc: Jonathan Corbet Cc: Kefeng Wang Cc: Liam Howlett Cc: Lorenzo Stoakes Cc: Michal Hocko Cc: Mike Rapoport Cc: Suren Baghdasaryan Cc: Vlastimil Babka Cc: ze zuo Signed-off-by: Andrew Morton

Docs/mm/damon/design: document 'address unit' parameter

2025-09-13T23:55:23+00:00

Add 'addr_unit' parameter description on DAMON design document. Link: https://lkml.kernel.org/r/20250828171242.59810-9-sj@kernel.org Signed-off-by: SeongJae Park Signed-off-by: Quanmin Yan Reviewed-by: SeongJae Park Cc: David Hildenbrand Cc: Jonathan Corbet Cc: Kefeng Wang Cc: Liam Howlett Cc: Lorenzo Stoakes Cc: Michal Hocko Cc: Mike Rapoport Cc: Suren Baghdasaryan Cc: Vlastimil Babka Cc: ze zuo Signed-off-by: Andrew Morton

docs/mm/damon/design: fix typo: s/sz_trtied/sz_tried/

2025-09-13T23:54:49+00:00

There are some typo in statistics section of DAMON design docs - sz_trtied -> sz_tried Link: https://lkml.kernel.org/r/20250729144414.31958-1-ekffu200098@gmail.com Signed-off-by: Sang-Heon Jeon Signed-off-by: SeongJae Park Reviewed-by: SeongJae Park Reviewed-by: Dev Jain Reviewed-by: Honggyu Kim Signed-off-by: Andrew Morton

docs: update physical memory documentation by adding N_GENERIC_INITIATOR to enum node_states

2025-08-11T17:03:37+00:00

While reading physical_memory.rst, I noticed that N_GENERIC_INITIATOR has not been update from the node_states list, even though it's already added in commit 894c26a1c274b8eafbb4b1dad67e70e51a106061. Signed-off-by: Kim Tae Hyun Acked-by: Mike Rapoport (Microsoft) Signed-off-by: Jonathan Corbet Link: https://lore.kernel.org/r/20250802125801.10068-1-kimth0312@gmail.com