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| author | Linus Torvalds <torvalds@linux-foundation.org> | 2018-06-04 12:34:27 -0700 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2018-06-04 12:34:27 -0700 |
| commit | eeee3149aaa022145b2659e3b0601dc705d69402 (patch) | |
| tree | 1b537cccc059cab62d7d2e22b7583b192d9e8c15 /Documentation/vm/overcommit-accounting | |
| parent | c5e7a7ea22d5677f7c70028908372cff6948ecdc (diff) | |
| parent | a49d9c0ae46e149a22aefa8251d07dddd5611851 (diff) | |
Merge tag 'docs-4.18' of git://git.lwn.net/linux
Pull documentation updates from Jonathan Corbet:
"There's been a fair amount of work in the docs tree this time around,
including:
- Extensive RST conversions and organizational work in the
memory-management docs thanks to Mike Rapoport.
- An update of Documentation/features from Andrea Parri and a script
to keep it updated.
- Various LICENSES updates from Thomas, along with a script to check
SPDX tags.
- Work to fix dangling references to documentation files; this
involved a fair number of one-liner comment changes outside of
Documentation/
... and the usual list of documentation improvements, typo fixes, etc"
* tag 'docs-4.18' of git://git.lwn.net/linux: (103 commits)
Documentation: document hung_task_panic kernel parameter
docs/admin-guide/mm: add high level concepts overview
docs/vm: move ksm and transhuge from "user" to "internals" section.
docs: Use the kerneldoc comments for memalloc_no*()
doc: document scope NOFS, NOIO APIs
docs: update kernel versions and dates in tables
docs/vm: transhuge: split userspace bits to admin-guide/mm/transhuge
docs/vm: transhuge: minor updates
docs/vm: transhuge: change sections order
Documentation: arm: clean up Marvell Berlin family info
Documentation: gpio: driver: Fix a typo and some odd grammar
docs: ranoops.rst: fix location of ramoops.txt
scripts/documentation-file-ref-check: rewrite it in perl with auto-fix mode
docs: uio-howto.rst: use a code block to solve a warning
mm, THP, doc: Add document for thp_swpout/thp_swpout_fallback
w1: w1_io.c: fix a kernel-doc warning
Documentation/process/posting: wrap text at 80 cols
docs: admin-guide: add cgroup-v2 documentation
Revert "Documentation/features/vm: Remove arch support status file for 'pte_special'"
Documentation: refcount-vs-atomic: Update reference to LKMM doc.
...
Diffstat (limited to 'Documentation/vm/overcommit-accounting')
| -rw-r--r-- | Documentation/vm/overcommit-accounting | 80 |
1 files changed, 0 insertions, 80 deletions
diff --git a/Documentation/vm/overcommit-accounting b/Documentation/vm/overcommit-accounting deleted file mode 100644 index cbfaaa674118..000000000000 --- a/Documentation/vm/overcommit-accounting +++ /dev/null @@ -1,80 +0,0 @@ -The Linux kernel supports the following overcommit handling modes - -0 - Heuristic overcommit handling. Obvious overcommits of - address space are refused. Used for a typical system. It - ensures a seriously wild allocation fails while allowing - overcommit to reduce swap usage. root is allowed to - allocate slightly more memory in this mode. This is the - default. - -1 - Always overcommit. Appropriate for some scientific - applications. Classic example is code using sparse arrays - and just relying on the virtual memory consisting almost - entirely of zero pages. - -2 - Don't overcommit. The total address space commit - for the system is not permitted to exceed swap + a - configurable amount (default is 50%) of physical RAM. - Depending on the amount you use, in most situations - this means a process will not be killed while accessing - pages but will receive errors on memory allocation as - appropriate. - - Useful for applications that want to guarantee their - memory allocations will be available in the future - without having to initialize every page. - -The overcommit policy is set via the sysctl `vm.overcommit_memory'. - -The overcommit amount can be set via `vm.overcommit_ratio' (percentage) -or `vm.overcommit_kbytes' (absolute value). - -The current overcommit limit and amount committed are viewable in -/proc/meminfo as CommitLimit and Committed_AS respectively. - -Gotchas -------- - -The C language stack growth does an implicit mremap. If you want absolute -guarantees and run close to the edge you MUST mmap your stack for the -largest size you think you will need. For typical stack usage this does -not matter much but it's a corner case if you really really care - -In mode 2 the MAP_NORESERVE flag is ignored. - - -How It Works ------------- - -The overcommit is based on the following rules - -For a file backed map - SHARED or READ-only - 0 cost (the file is the map not swap) - PRIVATE WRITABLE - size of mapping per instance - -For an anonymous or /dev/zero map - SHARED - size of mapping - PRIVATE READ-only - 0 cost (but of little use) - PRIVATE WRITABLE - size of mapping per instance - -Additional accounting - Pages made writable copies by mmap - shmfs memory drawn from the same pool - -Status ------- - -o We account mmap memory mappings -o We account mprotect changes in commit -o We account mremap changes in size -o We account brk -o We account munmap -o We report the commit status in /proc -o Account and check on fork -o Review stack handling/building on exec -o SHMfs accounting -o Implement actual limit enforcement - -To Do ------ -o Account ptrace pages (this is hard) |
