kernel/linux.git/Documentation/admin-guide/mm, branch v6.18.21

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() ...

Docs/admin-guide/mm/damon/start: add --target_pid to DAMOS example command

2025-09-21T21:22:37+00:00

The example command doesn't work [1] on the latest DAMON user-space tool, since --damos_action option is updated to receive multiple arguments, and hence cannot know if the final argument is for deductible monitoring target or an argument for --damos_action option. Add --target_pid option to let damo understand it is for target pid. Link: https://lkml.kernel.org/r/20250916032339.115817-5-sj@kernel.org Link: https://github.com/damonitor/damo/pull/32 [2] Signed-off-by: SeongJae Park Cc: David Hildenbrand Cc: Jonathan Corbet Cc: Joshua Hahn Cc: Liam Howlett Cc: Lorenzo Stoakes Cc: Michal Hocko Cc: Mike Rapoport Cc: Suren Baghdasaryan Cc: Vlastimil Babka Signed-off-by: Andrew Morton

mm: shmem: fix the strategy for the tmpfs 'huge=' options

2025-09-21T21:22:19+00:00

After commit acd7ccb284b8 ("mm: shmem: add large folio support for tmpfs"), we have extended tmpfs to allow any sized large folios, rather than just PMD-sized large folios. The strategy discussed previously was: : Considering that tmpfs already has the 'huge=' option to control the : PMD-sized large folios allocation, we can extend the 'huge=' option to : allow any sized large folios. The semantics of the 'huge=' mount option : are: : : huge=never: no any sized large folios : huge=always: any sized large folios : huge=within_size: like 'always' but respect the i_size : huge=advise: like 'always' if requested with madvise() : : Note: for tmpfs mmap() faults, due to the lack of a write size hint, still : allocate the PMD-sized huge folios if huge=always/within_size/advise is : set. : : Moreover, the 'deny' and 'force' testing options controlled by : '/sys/kernel/mm/transparent_hugepage/shmem_enabled', still retain the same : semantics. The 'deny' can disable any sized large folios for tmpfs, while : the 'force' can enable PMD sized large folios for tmpfs. This means that when tmpfs is mounted with 'huge=always' or 'huge=within_size', tmpfs will allow getting a highest order hint based on the size of write() and fallocate() paths. It will then try each allowable large order, rather than continually attempting to allocate PMD-sized large folios as before. However, this might break some user scenarios for those who want to use PMD-sized large folios, such as the i915 driver which did not supply a write size hint when allocating shmem [1]. Moreover, Hugh also complained that this will cause a regression in userspace with 'huge=always' or 'huge=within_size'. So, let's revisit the strategy for tmpfs large page allocation. A simple fix would be to always try PMD-sized large folios first, and if that fails, fall back to smaller large folios. This approach differs from the strategy for large folio allocation used by other file systems, however, tmpfs is somewhat different from other file systems, as quoted from David's opinion: : There were opinions in the past that tmpfs should just behave like any : other fs, and I think that's what we tried to satisfy here: use the write : size as an indication. : : I assume there will be workloads where either approach will be beneficial. : I also assume that workloads that use ordinary fs'es could benefit from : the same strategy (start with PMD), while others will clearly not. Link: https://lkml.kernel.org/r/10e7ac6cebe6535c137c064d5c5a235643eebb4a.1756888965.git.baolin.wang@linux.alibaba.com Link: https://lore.kernel.org/lkml/0d734549d5ed073c80b11601da3abdd5223e1889.1753689802.git.baolin.wang@linux.alibaba.com/ [1] Fixes: acd7ccb284b8 ("mm: shmem: add large folio support for tmpfs") Signed-off-by: Baolin Wang Cc: Barry Song Cc: David Hildenbrand Cc: Dev Jain Cc: Hugh Dickins Cc: Liam Howlett Cc: Lorenzo Stoakes Cc: Mariano Pache Cc: Matthew Wilcox (Oracle) Cc: Ryan Roberts Cc: Zi Yan Signed-off-by: Andrew Morton

mm: remove unused zpool layer

2025-09-21T21:21:59+00:00

With zswap using zsmalloc directly, there are no more in-tree users of this code. Remove it. With zpool gone, zsmalloc is now always a simple dependency and no longer something the user needs to configure. Hide CONFIG_ZSMALLOC from the user and have zswap and zram pull it in as needed. Link: https://lkml.kernel.org/r/20250829162212.208258-3-hannes@cmpxchg.org Signed-off-by: Johannes Weiner Acked-by: SeongJae Park Acked-by: Yosry Ahmed Cc: Chengming Zhou Cc: Nhat Pham Cc: Vitaly Wool 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: transhuge: document process level THP controls

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

This includes the PR_SET_THP_DISABLE/PR_GET_THP_DISABLE pair of prctl calls as well the newly introduced PR_THP_DISABLE_EXCEPT_ADVISED flag for the PR_SET_THP_DISABLE prctl call. Link: https://lkml.kernel.org/r/20250815135549.130506-5-usamaarif642@gmail.com Signed-off-by: Usama Arif Reviewed-by: Lorenzo Stoakes Reviewed-by: Zi Yan Cc: Arnd Bergmann Cc: Baolin Wang Cc: Barry Song Cc: David Hildenbrand 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

Documentation: Fix admin-guide typos

2025-08-18T16:31:19+00:00

Fix typos. Signed-off-by: Bjorn Helgaas Reviewed-by: Randy Dunlap Signed-off-by: Jonathan Corbet Link: https://lore.kernel.org/r/20250813200526.290420-4-helgaas@kernel.org

Merge tag 'mm-stable-2025-07-30-15-25' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

2025-07-31T21:57:54+00:00

Pull MM updates from Andrew Morton: "As usual, many cleanups. The below blurbiage describes 42 patchsets. 21 of those are partially or fully cleanup work. "cleans up", "cleanup", "maintainability", "rationalizes", etc. I never knew the MM code was so dirty. "mm: ksm: prevent KSM from breaking merging of new VMAs" (Lorenzo Stoakes) addresses an issue with KSM's PR_SET_MEMORY_MERGE mode: newly mapped VMAs were not eligible for merging with existing adjacent VMAs. "mm/damon: introduce DAMON_STAT for simple and practical access monitoring" (SeongJae Park) adds a new kernel module which simplifies the setup and usage of DAMON in production environments. "stop passing a writeback_control to swap/shmem writeout" (Christoph Hellwig) is a cleanup to the writeback code which removes a couple of pointers from struct writeback_control. "drivers/base/node.c: optimization and cleanups" (Donet Tom) contains largely uncorrelated cleanups to the NUMA node setup and management code. "mm: userfaultfd: assorted fixes and cleanups" (Tal Zussman) does some maintenance work on the userfaultfd code. "Readahead tweaks for larger folios" (Ryan Roberts) implements some tuneups for pagecache readahead when it is reading into order>0 folios. "selftests/mm: Tweaks to the cow test" (Mark Brown) provides some cleanups and consistency improvements to the selftests code. "Optimize mremap() for large folios" (Dev Jain) does that. A 37% reduction in execution time was measured in a memset+mremap+munmap microbenchmark. "Remove zero_user()" (Matthew Wilcox) expunges zero_user() in favor of the more modern memzero_page(). "mm/huge_memory: vmf_insert_folio_*() and vmf_insert_pfn_pud() fixes" (David Hildenbrand) addresses some warts which David noticed in the huge page code. These were not known to be causing any issues at this time. "mm/damon: use alloc_migrate_target() for DAMOS_MIGRATE_{HOT,COLD" (SeongJae Park) provides some cleanup and consolidation work in DAMON. "use vm_flags_t consistently" (Lorenzo Stoakes) uses vm_flags_t in places where we were inappropriately using other types. "mm/memfd: Reserve hugetlb folios before allocation" (Vivek Kasireddy) increases the reliability of large page allocation in the memfd code. "mm: Remove pXX_devmap page table bit and pfn_t type" (Alistair Popple) removes several now-unneeded PFN_* flags. "mm/damon: decouple sysfs from core" (SeongJae Park) implememnts some cleanup and maintainability work in the DAMON sysfs layer. "madvise cleanup" (Lorenzo Stoakes) does quite a lot of cleanup/maintenance work in the madvise() code. "madvise anon_name cleanups" (Vlastimil Babka) provides additional cleanups on top or Lorenzo's effort. "Implement numa node notifier" (Oscar Salvador) creates a standalone notifier for NUMA node memory state changes. Previously these were lumped under the more general memory on/offline notifier. "Make MIGRATE_ISOLATE a standalone bit" (Zi Yan) cleans up the pageblock isolation code and fixes a potential issue which doesn't seem to cause any problems in practice. "selftests/damon: add python and drgn based DAMON sysfs functionality tests" (SeongJae Park) adds additional drgn- and python-based DAMON selftests which are more comprehensive than the existing selftest suite. "Misc rework on hugetlb faulting path" (Oscar Salvador) fixes a rather obscure deadlock in the hugetlb fault code and follows that fix with a series of cleanups. "cma: factor out allocation logic from __cma_declare_contiguous_nid" (Mike Rapoport) rationalizes and cleans up the highmem-specific code in the CMA allocator. "mm/migration: rework movable_ops page migration (part 1)" (David Hildenbrand) provides cleanups and future-preparedness to the migration code. "mm/damon: add trace events for auto-tuned monitoring intervals and DAMOS quota" (SeongJae Park) adds some tracepoints to some DAMON auto-tuning code. "mm/damon: fix misc bugs in DAMON modules" (SeongJae Park) does that. "mm/damon: misc cleanups" (SeongJae Park) also does what it claims. "mm: folio_pte_batch() improvements" (David Hildenbrand) cleans up the large folio PTE batching code. "mm/damon/vaddr: Allow interleaving in migrate_{hot,cold} actions" (SeongJae Park) facilitates dynamic alteration of DAMON's inter-node allocation policy. "Remove unmap_and_put_page()" (Vishal Moola) provides a couple of page->folio conversions. "mm: per-node proactive reclaim" (Davidlohr Bueso) implements a per-node control of proactive reclaim - beyond the current memcg-based implementation. "mm/damon: remove damon_callback" (SeongJae Park) replaces the damon_callback interface with a more general and powerful damon_call()+damos_walk() interface. "mm/mremap: permit mremap() move of multiple VMAs" (Lorenzo Stoakes) implements a number of mremap cleanups (of course) in preparation for adding new mremap() functionality: newly permit the remapping of multiple VMAs when the user is specifying MREMAP_FIXED. It still excludes some specialized situations where this cannot be performed reliably. "drop hugetlb_free_pgd_range()" (Anthony Yznaga) switches some sparc hugetlb code over to the generic version and removes the thus-unneeded hugetlb_free_pgd_range(). "mm/damon/sysfs: support periodic and automated stats update" (SeongJae Park) augments the present userspace-requested update of DAMON sysfs monitoring files. Automatic update is now provided, along with a tunable to control the update interval. "Some randome fixes and cleanups to swapfile" (Kemeng Shi) does what is claims. "mm: introduce snapshot_page" (Luiz Capitulino and David Hildenbrand) provides (and uses) a means by which debug-style functions can grab a copy of a pageframe and inspect it locklessly without tripping over the races inherent in operating on the live pageframe directly. "use per-vma locks for /proc/pid/maps reads" (Suren Baghdasaryan) addresses the large contention issues which can be triggered by reads from that procfs file. Latencies are reduced by more than half in some situations. The series also introduces several new selftests for the /proc/pid/maps interface. "__folio_split() clean up" (Zi Yan) cleans up __folio_split()! "Optimize mprotect() for large folios" (Dev Jain) provides some quite large (>3x) speedups to mprotect() when dealing with large folios. "selftests/mm: reuse FORCE_READ to replace "asm volatile("" : "+r" (XXX));" and some cleanup" (wang lian) does some cleanup work in the selftests code. "tools/testing: expand mremap testing" (Lorenzo Stoakes) extends the mremap() selftest in several ways, including adding more checking of Lorenzo's recently added "permit mremap() move of multiple VMAs" feature. "selftests/damon/sysfs.py: test all parameters" (SeongJae Park) extends the DAMON sysfs interface selftest so that it tests all possible user-requested parameters. Rather than the present minimal subset" * tag 'mm-stable-2025-07-30-15-25' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm: (370 commits) MAINTAINERS: add missing headers to mempory policy & migration section MAINTAINERS: add missing file to cgroup section MAINTAINERS: add MM MISC section, add missing files to MISC and CORE MAINTAINERS: add missing zsmalloc file MAINTAINERS: add missing files to page alloc section MAINTAINERS: add missing shrinker files MAINTAINERS: move memremap.[ch] to hotplug section MAINTAINERS: add missing mm_slot.h file THP section MAINTAINERS: add missing interval_tree.c to memory mapping section MAINTAINERS: add missing percpu-internal.h file to per-cpu section mm/page_alloc: remove trace_mm_alloc_contig_migrate_range_info() selftests/damon: introduce _common.sh to host shared function selftests/damon/sysfs.py: test runtime reduction of DAMON parameters selftests/damon/sysfs.py: test non-default parameters runtime commit selftests/damon/sysfs.py: generalize DAMON context commit assertion selftests/damon/sysfs.py: generalize monitoring attributes commit assertion selftests/damon/sysfs.py: generalize DAMOS schemes commit assertion selftests/damon/sysfs.py: test DAMOS filters commitment selftests/damon/sysfs.py: generalize DAMOS scheme commit assertion selftests/damon/sysfs.py: test DAMOS destinations commitment ...

docs: update THP documentation to clarify sysfs "never" setting

2025-07-25T02:12:43+00:00

Rather confusingly, setting all Transparent Huge Page sysfs settings to "never" does not in fact result in THP being globally disabled. Rather, it results in khugepaged being disabled, but one can still obtain THP pages using madvise(..., MADV_COLLAPSE). This is something that has remained poorly documented for some time, and it is likely the received wisdom of most users of THP that never does, in fact, mean never. It is therefore important to highlight, very clearly, that this is not the case. [lorenzo.stoakes@oracle.com: update transhuge page to mention MADV_COLLAPSE] Link: https://lkml.kernel.org/r/d54d1dfb-f06d-4979-983b-73998f05867e@lucifer.local Link: https://lkml.kernel.org/r/20250721155530.75944-1-lorenzo.stoakes@oracle.com Signed-off-by: Lorenzo Stoakes Acked-by: SeongJae Park Reviewed-by: Zi Yan Reviewed-by: Baolin Wang Reviewed-by: Barry Song Acked-by: David Hildenbrand Cc: Dev Jain Cc: Jonathan Corbet Cc: Liam Howlett Cc: Mariano Pache Cc: Ryan Roberts Signed-off-by: Andrew Morton

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

2025-07-25T02:12:33+00:00

Document the new DAMON sysfs file, refresh_ms, on the usage document. Link: https://lkml.kernel.org/r/20250717055448.56976-4-sj@kernel.org Signed-off-by: SeongJae Park Cc: Jonathan Corbet Signed-off-by: Andrew Morton