linux.git/Documentation/admin-guide/mm, branch v6.10-rc6

mm: drop the 'anon_' prefix for swap-out mTHP counters

2024-06-06T02:19:23+00:00

The mTHP swap related counters: 'anon_swpout' and 'anon_swpout_fallback'
are confusing with an 'anon_' prefix, since the shmem can swap out
non-anonymous pages.  So drop the 'anon_' prefix to keep consistent with
the old swap counter names.

This is needed in 6.10-rcX to avoid having an inconsistent ABI out in the
field.

Link: https://lkml.kernel.org/r/7a8989c13299920d7589007a30065c3e2c19f0e0.1716431702.git.baolin.wang@linux.alibaba.com
Fixes: d0f048ac39f6 ("mm: add per-order mTHP anon_swpout and anon_swpout_fallback counters")
Fixes: 42248b9d34ea ("mm: add docs for per-order mTHP counters and transhuge_page ABI")
Signed-off-by: Baolin Wang 
Suggested-by: "Huang, Ying" 
Acked-by: Barry Song 
Cc: David Hildenbrand 
Cc: Lance Yang 
Cc: Matthew Wilcox (Oracle) 
Cc: Ryan Roberts 
Cc: Zi Yan 
Signed-off-by: Andrew Morton

Merge tag 'mm-stable-2024-05-17-19-19' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

2024-05-19T16:21:03+00:00

Pull mm updates from Andrew Morton:
"The usual shower of singleton fixes and minor series all over MM,
documented (hopefully adequately) in the respective changelogs.
Notable series include:

- Lucas Stach has provided some page-mapping cleanup/consolidation/
maintainability work in the series "mm/treewide: Remove pXd_huge()
API".

- In the series "Allow migrate on protnone reference with
MPOL_PREFERRED_MANY policy", Donet Tom has optimized mempolicy's
MPOL_PREFERRED_MANY mode, yielding almost doubled performance in
one test.

- In their series "Memory allocation profiling" Kent Overstreet and
Suren Baghdasaryan have contributed a means of determining (via
/proc/allocinfo) whereabouts in the kernel memory is being
allocated: number of calls and amount of memory.

- Matthew Wilcox has provided the series "Various significant MM
patches" which does a number of rather unrelated things, but in
largely similar code sites.

- In his series "mm: page_alloc: freelist migratetype hygiene"
Johannes Weiner has fixed the page allocator's handling of
migratetype requests, with resulting improvements in compaction
efficiency.

- In the series "make the hugetlb migration strategy consistent"
Baolin Wang has fixed a hugetlb migration issue, which should
improve hugetlb allocation reliability.

- Liu Shixin has hit an I/O meltdown caused by readahead in a
memory-tight memcg. Addressed in the series "Fix I/O high when
memory almost met memcg limit".

- In the series "mm/filemap: optimize folio adding and splitting"
Kairui Song has optimized pagecache insertion, yielding ~10%
performance improvement in one test.

- Baoquan He has cleaned up and consolidated the early zone
initialization code in the series "mm/mm_init.c: refactor
free_area_init_core()".

- Baoquan has also redone some MM initializatio code in the series
"mm/init: minor clean up and improvement".

- MM helper cleanups from Christoph Hellwig in his series "remove
follow_pfn".

- More cleanups from Matthew Wilcox in the series "Various
page->flags cleanups".

- Vlastimil Babka has contributed maintainability improvements in the
series "memcg_kmem hooks refactoring".

- More folio conversions and cleanups in Matthew Wilcox's series:
"Convert huge_zero_page to huge_zero_folio"
"khugepaged folio conversions"
"Remove page_idle and page_young wrappers"
"Use folio APIs in procfs"
"Clean up __folio_put()"
"Some cleanups for memory-failure"
"Remove page_mapping()"
"More folio compat code removal"

- David Hildenbrand chipped in with "fs/proc/task_mmu: convert
hugetlb functions to work on folis".

- Code consolidation and cleanup work related to GUP's handling of
hugetlbs in Peter Xu's series "mm/gup: Unify hugetlb, part 2".

- Rick Edgecombe has developed some fixes to stack guard gaps in the
series "Cover a guard gap corner case".

- Jinjiang Tu has fixed KSM's behaviour after a fork+exec in the
series "mm/ksm: fix ksm exec support for prctl".

- Baolin Wang has implemented NUMA balancing for multi-size THPs.
This is a simple first-cut implementation for now. The series is
"support multi-size THP numa balancing".

- Cleanups to vma handling helper functions from Matthew Wilcox in
the series "Unify vma_address and vma_pgoff_address".

- Some selftests maintenance work from Dev Jain in the series
"selftests/mm: mremap_test: Optimizations and style fixes".

- Improvements to the swapping of multi-size THPs from Ryan Roberts
in the series "Swap-out mTHP without splitting".

- Kefeng Wang has significantly optimized the handling of arm64's
permission page faults in the series
"arch/mm/fault: accelerate pagefault when badaccess"
"mm: remove arch's private VM_FAULT_BADMAP/BADACCESS"

- GUP cleanups from David Hildenbrand in "mm/gup: consistently call
it GUP-fast".

- hugetlb fault code cleanups from Vishal Moola in "Hugetlb fault
path to use struct vm_fault".

- selftests build fixes from John Hubbard in the series "Fix
selftests/mm build without requiring "make headers"".

- Memory tiering fixes/improvements from Ho-Ren (Jack) Chuang in the
series "Improved Memory Tier Creation for CPUless NUMA Nodes".
Fixes the initialization code so that migration between different
memory types works as intended.

- David Hildenbrand has improved follow_pte() and fixed an errant
driver in the series "mm: follow_pte() improvements and acrn
follow_pte() fixes".

- David also did some cleanup work on large folio mapcounts in his
series "mm: mapcount for large folios + page_mapcount() cleanups".

- Folio conversions in KSM in Alex Shi's series "transfer page to
folio in KSM".

- Barry Song has added some sysfs stats for monitoring multi-size
THP's in the series "mm: add per-order mTHP alloc and swpout
counters".

- Some zswap cleanups from Yosry Ahmed in the series "zswap
same-filled and limit checking cleanups".

- Matthew Wilcox has been looking at buffer_head code and found the
documentation to be lacking. The series is "Improve buffer head
documentation".

- Multi-size THPs get more work, this time from Lance Yang. His
series "mm/madvise: enhance lazyfreeing with mTHP in madvise_free"
optimizes the freeing of these things.

- Kemeng Shi has added more userspace-visible writeback
instrumentation in the series "Improve visibility of writeback".

- Kemeng Shi then sent some maintenance work on top in the series
"Fix and cleanups to page-writeback".

- Matthew Wilcox reduces mmap_lock traffic in the anon vma code in
the series "Improve anon_vma scalability for anon VMAs". Intel's
test bot reported an improbable 3x improvement in one test.

- SeongJae Park adds some DAMON feature work in the series
"mm/damon: add a DAMOS filter type for page granularity access recheck"
"selftests/damon: add DAMOS quota goal test"

- Also some maintenance work in the series
"mm/damon/paddr: simplify page level access re-check for pageout"
"mm/damon: misc fixes and improvements"

- David Hildenbrand has disabled some known-to-fail selftests ni the
series "selftests: mm: cow: flag vmsplice() hugetlb tests as
XFAIL".

- memcg metadata storage optimizations from Shakeel Butt in "memcg:
reduce memory consumption by memcg stats".

- DAX fixes and maintenance work from Vishal Verma in the series
"dax/bus.c: Fixups for dax-bus locking""

* tag 'mm-stable-2024-05-17-19-19' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm: (426 commits)
memcg, oom: cleanup unused memcg_oom_gfp_mask and memcg_oom_order
selftests/mm: hugetlb_madv_vs_map: avoid test skipping by querying hugepage size at runtime
mm/hugetlb: add missing VM_FAULT_SET_HINDEX in hugetlb_wp
mm/hugetlb: add missing VM_FAULT_SET_HINDEX in hugetlb_fault
selftests: cgroup: add tests to verify the zswap writeback path
mm: memcg: make alloc_mem_cgroup_per_node_info() return bool
mm/damon/core: fix return value from damos_wmark_metric_value
mm: do not update memcg stats for NR_{FILE/SHMEM}_PMDMAPPED
selftests: cgroup: remove redundant enabling of memory controller
Docs/mm/damon/maintainer-profile: allow posting patches based on damon/next tree
Docs/mm/damon/maintainer-profile: change the maintainer's timezone from PST to PT
Docs/mm/damon/design: use a list for supported filters
Docs/admin-guide/mm/damon/usage: fix wrong schemes effective quota update command
Docs/admin-guide/mm/damon/usage: fix wrong example of DAMOS filter matching sysfs file
selftests/damon: classify tests for functionalities and regressions
selftests/damon/_damon_sysfs: use 'is' instead of '==' for 'None'
selftests/damon/_damon_sysfs: find sysfs mount point from /proc/mounts
selftests/damon/_damon_sysfs: check errors from nr_schemes file reads
mm/damon/core: initialize ->esz_bp from damos_quota_init_priv()
selftests/damon: add a test for DAMOS quota goal
...

Docs/admin-guide/mm/damon/usage: fix wrong schemes effective quota update command

2024-05-11T22:41:34+00:00

To update effective size quota of DAMOS schemes on DAMON sysfs file
interface, user should write 'update_schemes_effective_quotas' to the
kdamond 'state' file.  But the document is mistakenly saying the input
string as 'update_schemes_effective_bytes'.  Fix it (s/bytes/quotas/).

Link: https://lkml.kernel.org/r/20240503180318.72798-8-sj@kernel.org
Fixes: a6068d6dfa2f ("Docs/admin-guide/mm/damon/usage: document effective_bytes file")
Signed-off-by: SeongJae Park 
Cc: 	[6.9.x]
Cc: Jonathan Corbet 
Cc: Shuah Khan 
Signed-off-by: Andrew Morton

Docs/admin-guide/mm/damon/usage: fix wrong example of DAMOS filter matching sysfs file

2024-05-11T22:41:34+00:00

The example usage of DAMOS filter sysfs files, specifically the part of
'matching' file writing for memcg type filter, is wrong.  The intention is
to exclude pages of a memcg that already getting enough care from a given
scheme, but the example is setting the filter to apply the scheme to only
the pages of the memcg.  Fix it.

Link: https://lkml.kernel.org/r/20240503180318.72798-7-sj@kernel.org
Fixes: 9b7f9322a530 ("Docs/admin-guide/mm/damon/usage: document DAMOS filters of sysfs")
Closes: https://lore.kernel.org/r/20240317191358.97578-1-sj@kernel.org
Signed-off-by: SeongJae Park 
Cc: 	[6.3.x]
Cc: Jonathan Corbet 
Cc: Shuah Khan 
Signed-off-by: Andrew Morton

Docs/admin-guide/mm/damon/usage: update for young page type DAMOS filter

2024-05-06T00:53:55+00:00

Update DAMON usage document for the newly added DAMOS filter type, 'young
page'.

Link: https://lkml.kernel.org/r/20240426195247.100306-7-sj@kernel.org
Signed-off-by: SeongJae Park 
Cc: Honggyu Kim 
Cc: Jonathan Corbet 
Signed-off-by: Andrew Morton

mm/khugepaged: replace page_mapcount() check by folio_likely_mapped_shared()

2024-05-06T00:53:50+00:00

We want to limit the use of page_mapcount() to places where absolutely
required, to prepare for kernel configs where we won't keep track of
per-page mapcounts in large folios.

khugepaged is one of the remaining "more challenging" page_mapcount()
users, but we might be able to move away from page_mapcount() without
resulting in a significant behavior change that would warrant
special-casing based on kernel configs.

In 2020, we first added support to khugepaged for collapsing COW-shared
pages via commit 9445689f3b61 ("khugepaged: allow to collapse a page
shared across fork"), followed by support for collapsing PTE-mapped THP in
commit 5503fbf2b0b8 ("khugepaged: allow to collapse PTE-mapped compound
pages") and limiting the memory waste via the "page_count() > 1" check in
commit 71a2c112a0f6 ("khugepaged: introduce 'max_ptes_shared' tunable").

As a default, khugepaged will allow up to half of the PTEs to map shared
pages: where page_mapcount() > 1.  MADV_COLLAPSE ignores the khugepaged
setting.

khugepaged does currently not care about swapcache page references, and
does not check under folio lock: so in some corner cases the "shared vs. 
exclusive" detection might be a bit off, making us detect "exclusive" when
it's actually "shared".

Most of our anonymous folios in the system are usually exclusive.  We
frequently see sharing of anonymous folios for a short period of time,
after which our short-lived suprocesses either quit or exec().

There are some famous examples, though, where child processes exist for a
long time, and where memory is COW-shared with a lot of processes
(webservers, webbrowsers, sshd, ...) and COW-sharing is crucial for
reducing the memory footprint.  We don't want to suddenly change the
behavior to result in a significant increase in memory waste.

Interestingly, khugepaged will only collapse an anonymous THP if at least
one PTE is writable.  After fork(), that means that something (usually a
page fault) populated at least a single exclusive anonymous THP in that
PMD range.

So ...  what happens when we switch to "is this folio mapped shared"
instead of "is this page mapped shared" by using
folio_likely_mapped_shared()?

For "not-COW-shared" folios, small folios and for THPs (large folios) that
are completely mapped into at least one process, switching to
folio_likely_mapped_shared() will not result in a change.

We'll only see a change for COW-shared PTE-mapped THPs that are partially
mapped into all involved processes.

There are two cases to consider:

(A) folio_likely_mapped_shared() returns "false" for a PTE-mapped THP

  If the folio is detected as exclusive, and it actually is exclusive,
  there is no change: page_mapcount() == 1. This is the common case
  without fork() or with short-lived child processes.

  folio_likely_mapped_shared() might currently still detect a folio as
  exclusive although it is shared (false negatives): if the first page is
  not mapped multiple times and if the average per-page mapcount is smaller
  than 1, implying that (1) the folio is partially mapped and (2) if we are
  responsible for many mapcounts by mapping many pages others can't
  ("mostly exclusive") (3) if we are not responsible for many mapcounts by
  mapping little pages ("mostly shared") it won't make a big impact on the
  end result.

  So while we might now detect a page as "exclusive" although it isn't,
  it's not expected to make a big difference in common cases.

(B) folio_likely_mapped_shared() returns "true" for a PTE-mapped THP

  folio_likely_mapped_shared() will never detect a large anonymous folio
  as shared although it is exclusive: there are no false positives.

  If we detect a THP as shared, at least one page of the THP is mapped by
  another process. It could well be that some pages are actually exclusive.
  For example, our child processes could have unmapped/COW'ed some pages
  such that they would now be exclusive to out process, which we now
  would treat as still-shared.

  Examples:
  (1) Parent maps all pages of a THP, child maps some pages. We detect
      all pages in the parent as shared although some are actually
      exclusive.
  (2) Parent maps all but some page of a THP, child maps the remainder.
      We detect all pages of the THP that the parent maps as shared
      although they are all exclusive.

  In (1) we wouldn't collapse a THP right now already: no PTE
  is writable, because a write fault would have resulted in COW of a
  single page and the parent would no longer map all pages of that THP.

  For (2) we would have collapsed a THP in the parent so far, now we
  wouldn't as long as the child process is still alive: unless the child
  process unmaps the remaining THP pages or we decide to split that THP.

  Possibly, the child COW'ed many pages, meaning that it's likely that
  we can populate a THP for our child first, and then for our parent.

  For (2), we are making really bad use of the THP in the first
  place (not even mapped completely in at least one process). If the
  THP would be completely partially mapped, it would be on the deferred
  split queue where we would split it lazily later.

  For short-running child processes, we don't particularly care. For
  long-running processes, the expectation is that such scenarios are
  rather rare: further, a THP might be best placed if most data in the
  PMD range is actually written, implying that we'll have to COW more
  pages first before khugepaged would collapse it.

To summarize, in the common case, this change is not expected to matter
much.  The more common application of khugepaged operates on exclusive
pages, either before fork() or after a child quit.

Can we improve (A)?  Yes, if we implement more precise tracking of "mapped
shared" vs.  "mapped exclusively", we could get rid of the false negatives
completely.

Can we improve (B)?  We could count how many pages of a large folio we map
inside the current page table and detect that we are responsible for most
of the folio mapcount and conclude "as good as exclusive", which might
help in some cases.  ...  but likely, some other mechanism should detect
that the THP is not a good use in the scenario (not even mapped completely
in a single process) and try splitting that folio lazily etc.

We'll move the folio_test_anon() check before our "shared" check, so we
might get more expressive results for SCAN_EXCEED_SHARED_PTE: this order
of checks now matches the one in __collapse_huge_page_isolate().  Extend
documentation.

Link: https://lkml.kernel.org/r/20240424122630.495788-1-david@redhat.com
Signed-off-by: David Hildenbrand 
Cc: Jonathan Corbet 
Cc: Kirill A. Shutemov 
Cc: Zi Yan 
Cc: Yang Shi 
Cc: John Hubbard 
Cc: Ryan Roberts 
Signed-off-by: Andrew Morton

mm: zswap: remove same_filled module params

2024-05-06T00:53:38+00:00

These knobs offer more fine-grained control to userspace than needed and
directly expose/influence kernel implementation; remove them.

For disabling same_filled handling, there is no logical reason to refuse
storing same-filled pages more efficiently and opt for compression. 
Scanning pages for patterns may be an argument, but the page contents will
be read into the CPU cache anyway during compression.  Also, removing the
same_filled handling code does not move the needle significantly in terms
of performance anyway [1].

For disabling non_same_filled handling, it was added when the compressed
pages in zswap were not being properly charged to memcgs, as workloads
could escape the accounting with compression [2].  This is no longer the
case after commit f4840ccfca25 ("zswap: memcg accounting"), and using
zswap without compression does not make much sense.

[1]https://lore.kernel.org/lkml/CAJD7tkaySFP2hBQw4pnZHJJwe3bMdjJ1t9VC2VJd=khn1_TXvA@mail.gmail.com/
[2]https://lore.kernel.org/lkml/19d5cdee-2868-41bd-83d5-6da75d72e940@maciej.szmigiero.name/

[yosryahmed@google.com: remove same_filled_pages from docs]
  Link: https://lkml.kernel.org/r/ZhxFVggdyvCo79jc@google.com
Link: https://lkml.kernel.org/r/20240413022407.785696-5-yosryahmed@google.com
Signed-off-by: Yosry Ahmed 
Acked-by: Johannes Weiner 
Reviewed-by: Nhat Pham 
Reviewed-by: Chengming Zhou 
Cc: "Maciej S. Szmigiero" 
Signed-off-by: Andrew Morton

mm: correct the docs for thp_fault_alloc and thp_fault_fallback

2024-05-06T00:53:36+00:00

The documentation does not align with the code.  In
__do_huge_pmd_anonymous_page(), THP_FAULT_FALLBACK is incremented when
mem_cgroup_charge() fails, despite the allocation succeeding, whereas
THP_FAULT_ALLOC is only incremented after a successful charge.

Link: https://lkml.kernel.org/r/20240412114858.407208-5-21cnbao@gmail.com
Signed-off-by: Barry Song 
Reviewed-by: Ryan Roberts 
Reviewed-by: David Hildenbrand 
Cc: Chris Li 
Cc: Domenico Cerasuolo 
Cc: Kairui Song 
Cc: Matthew Wilcox (Oracle) 
Cc: Peter Xu 
Cc: Ryan Roberts 
Cc: Suren Baghdasaryan 
Cc: Yosry Ahmed 
Cc: Yu Zhao 
Cc: Jonathan Corbet 
Signed-off-by: Andrew Morton

mm: add docs for per-order mTHP counters and transhuge_page ABI

2024-05-06T00:53:36+00:00

This patch includes documentation for mTHP counters and an ABI file for
sys-kernel-mm-transparent-hugepage, which appears to have been missing for
some time.

[v-songbaohua@oppo.com: fix the name and unexpected indentation]
  Link: https://lkml.kernel.org/r/20240415054538.17071-1-21cnbao@gmail.com
Link: https://lkml.kernel.org/r/20240412114858.407208-4-21cnbao@gmail.com
Signed-off-by: Barry Song 
Reviewed-by: Ryan Roberts 
Reviewed-by: David Hildenbrand 
Cc: Chris Li 
Cc: Domenico Cerasuolo 
Cc: Kairui Song 
Cc: Matthew Wilcox (Oracle) 
Cc: Peter Xu 
Cc: Ryan Roberts 
Cc: Suren Baghdasaryan 
Cc: Yosry Ahmed 
Cc: Yu Zhao 
Cc: Jonathan Corbet 
Signed-off-by: Andrew Morton

Docs: typos/spelling

2024-05-02T16:02:29+00:00

Fix spelling and grammar in Docs descriptions

Signed-off-by: Remington Brasga 
Reviewed-by: Randy Dunlap 
Signed-off-by: Jonathan Corbet 
Link: https://lore.kernel.org/r/20240429225527.2329-1-rbrasga@uci.edu