6614a3c316
Lin, Yang Shi, Anshuman Khandual and Mike Rapoport
- Some kmemleak fixes from Patrick Wang and Waiman Long
- DAMON updates from SeongJae Park
- memcg debug/visibility work from Roman Gushchin
- vmalloc speedup from Uladzislau Rezki
- more folio conversion work from Matthew Wilcox
- enhancements for coherent device memory mapping from Alex Sierra
- addition of shared pages tracking and CoW support for fsdax, from
Shiyang Ruan
- hugetlb optimizations from Mike Kravetz
- Mel Gorman has contributed some pagealloc changes to improve latency
and realtime behaviour.
- mprotect soft-dirty checking has been improved by Peter Xu
- Many other singleton patches all over the place
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Merge tag 'mm-stable-2022-08-03' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
Pull MM updates from Andrew Morton:
"Most of the MM queue. A few things are still pending.
Liam's maple tree rework didn't make it. This has resulted in a few
other minor patch series being held over for next time.
Multi-gen LRU still isn't merged as we were waiting for mapletree to
stabilize. The current plan is to merge MGLRU into -mm soon and to
later reintroduce mapletree, with a view to hopefully getting both
into 6.1-rc1.
Summary:
- The usual batches of cleanups from Baoquan He, Muchun Song, Miaohe
Lin, Yang Shi, Anshuman Khandual and Mike Rapoport
- Some kmemleak fixes from Patrick Wang and Waiman Long
- DAMON updates from SeongJae Park
- memcg debug/visibility work from Roman Gushchin
- vmalloc speedup from Uladzislau Rezki
- more folio conversion work from Matthew Wilcox
- enhancements for coherent device memory mapping from Alex Sierra
- addition of shared pages tracking and CoW support for fsdax, from
Shiyang Ruan
- hugetlb optimizations from Mike Kravetz
- Mel Gorman has contributed some pagealloc changes to improve
latency and realtime behaviour.
- mprotect soft-dirty checking has been improved by Peter Xu
- Many other singleton patches all over the place"
[ XFS merge from hell as per Darrick Wong in
https://lore.kernel.org/all/YshKnxb4VwXycPO8@magnolia/ ]
* tag 'mm-stable-2022-08-03' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm: (282 commits)
tools/testing/selftests/vm/hmm-tests.c: fix build
mm: Kconfig: fix typo
mm: memory-failure: convert to pr_fmt()
mm: use is_zone_movable_page() helper
hugetlbfs: fix inaccurate comment in hugetlbfs_statfs()
hugetlbfs: cleanup some comments in inode.c
hugetlbfs: remove unneeded header file
hugetlbfs: remove unneeded hugetlbfs_ops forward declaration
hugetlbfs: use helper macro SZ_1{K,M}
mm: cleanup is_highmem()
mm/hmm: add a test for cross device private faults
selftests: add soft-dirty into run_vmtests.sh
selftests: soft-dirty: add test for mprotect
mm/mprotect: fix soft-dirty check in can_change_pte_writable()
mm: memcontrol: fix potential oom_lock recursion deadlock
mm/gup.c: fix formatting in check_and_migrate_movable_page()
xfs: fail dax mount if reflink is enabled on a partition
mm/memcontrol.c: remove the redundant updating of stats_flush_threshold
userfaultfd: don't fail on unrecognized features
hugetlb_cgroup: fix wrong hugetlb cgroup numa stat
...
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=====================
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Overcommit Accounting
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=====================
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The Linux kernel supports the following overcommit handling modes
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0
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Heuristic overcommit handling. Obvious overcommits of address
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space are refused. Used for a typical system. It ensures a
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seriously wild allocation fails while allowing overcommit to
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reduce swap usage. root is allowed to allocate slightly more
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memory in this mode. This is the default.
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1
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Always overcommit. Appropriate for some scientific
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applications. Classic example is code using sparse arrays and
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just relying on the virtual memory consisting almost entirely
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of zero pages.
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2
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Don't overcommit. The total address space commit for the
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system is not permitted to exceed swap + a configurable amount
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(default is 50%) of physical RAM. Depending on the amount you
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use, in most situations this means a process will not be
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killed while accessing pages but will receive errors on memory
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allocation as appropriate.
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Useful for applications that want to guarantee their memory
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allocations will be available in the future without having to
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initialize every page.
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The overcommit policy is set via the sysctl ``vm.overcommit_memory``.
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The overcommit amount can be set via ``vm.overcommit_ratio`` (percentage)
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or ``vm.overcommit_kbytes`` (absolute value). These only have an effect
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when ``vm.overcommit_memory`` is set to 2.
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The current overcommit limit and amount committed are viewable in
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``/proc/meminfo`` as CommitLimit and Committed_AS respectively.
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Gotchas
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=======
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The C language stack growth does an implicit mremap. If you want absolute
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guarantees and run close to the edge you MUST mmap your stack for the
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largest size you think you will need. For typical stack usage this does
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not matter much but it's a corner case if you really really care
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In mode 2 the MAP_NORESERVE flag is ignored.
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How It Works
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============
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The overcommit is based on the following rules
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For a file backed map
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| SHARED or READ-only - 0 cost (the file is the map not swap)
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| PRIVATE WRITABLE - size of mapping per instance
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For an anonymous or ``/dev/zero`` map
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| SHARED - size of mapping
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| PRIVATE READ-only - 0 cost (but of little use)
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| PRIVATE WRITABLE - size of mapping per instance
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Additional accounting
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| Pages made writable copies by mmap
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| shmfs memory drawn from the same pool
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Status
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======
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* We account mmap memory mappings
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* We account mprotect changes in commit
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* We account mremap changes in size
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* We account brk
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* We account munmap
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* We report the commit status in /proc
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* Account and check on fork
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* Review stack handling/building on exec
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* SHMfs accounting
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* Implement actual limit enforcement
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To Do
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=====
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* Account ptrace pages (this is hard)
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