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 ===============================
 Documentation for /proc/sys/vm/
 ===============================
 
 kernel version 2.6.29
 
 Copyright (c) 1998, 1999,  Rik van Riel <riel@nl.linux.org>
 
 Copyright (c) 2008         Peter W. Morreale <pmorreale@novell.com>
 
 For general info and legal blurb, please look in index.rst.
 
 ------------------------------------------------------------------------------
 
 This file contains the documentation for the sysctl files in
 /proc/sys/vm and is valid for Linux kernel version 2.6.29.
 
 The files in this directory can be used to tune the operation
 of the virtual memory (VM) subsystem of the Linux kernel and
 the writeout of dirty data to disk.
 
 Default values and initialization routines for most of these
 files can be found in mm/swap.c.
 
 Currently, these files are in /proc/sys/vm:
 
 - admin_reserve_kbytes
 - compact_memory
 - compaction_proactiveness
 - compact_unevictable_allowed
 - dirty_background_bytes
 - dirty_background_ratio
 - dirty_bytes
 - dirty_expire_centisecs
 - dirty_ratio
 - dirtytime_expire_seconds
 - dirty_writeback_centisecs
 - drop_caches
 - extfrag_threshold
 - highmem_is_dirtyable
 - hugetlb_shm_group
 - laptop_mode
 - legacy_va_layout
 - lowmem_reserve_ratio
 - max_map_count
 - memory_failure_early_kill
 - memory_failure_recovery
 - min_free_kbytes
 - min_slab_ratio
 - min_unmapped_ratio
 - mmap_min_addr
 - mmap_rnd_bits
 - mmap_rnd_compat_bits
 - nr_hugepages
 - nr_hugepages_mempolicy
 - nr_overcommit_hugepages
 - nr_trim_pages         (only if CONFIG_MMU=n)
 - numa_zonelist_order
 - oom_dump_tasks
 - oom_kill_allocating_task
 - overcommit_kbytes
 - overcommit_memory
 - overcommit_ratio
 - page-cluster
 - page_lock_unfairness
 - panic_on_oom
 - percpu_pagelist_high_fraction
 - stat_interval
 - stat_refresh
 - numa_stat
 - swappiness
 - unprivileged_userfaultfd
 - user_reserve_kbytes
 - vfs_cache_pressure
 - watermark_boost_factor
 - watermark_scale_factor
 - zone_reclaim_mode
 
 
 admin_reserve_kbytes
 ====================
 
 The amount of free memory in the system that should be reserved for users
 with the capability cap_sys_admin.
 
 admin_reserve_kbytes defaults to min(3% of free pages, 8MB)
 
 That should provide enough for the admin to log in and kill a process,
 if necessary, under the default overcommit 'guess' mode.
 
 Systems running under overcommit 'never' should increase this to account
 for the full Virtual Memory Size of programs used to recover. Otherwise,
 root may not be able to log in to recover the system.
 
 How do you calculate a minimum useful reserve?
 
 sshd or login + bash (or some other shell) + top (or ps, kill, etc.)
 
 For overcommit 'guess', we can sum resident set sizes (RSS).
 On x86_64 this is about 8MB.
 
 For overcommit 'never', we can take the max of their virtual sizes (VSZ)
 and add the sum of their RSS.
 On x86_64 this is about 128MB.
 
 Changing this takes effect whenever an application requests memory.
 
 
 compact_memory
 ==============
 
 Available only when CONFIG_COMPACTION is set. When 1 is written to the file,
 all zones are compacted such that free memory is available in contiguous
 blocks where possible. This can be important for example in the allocation of
 huge pages although processes will also directly compact memory as required.
 
 compaction_proactiveness
 ========================
 
 This tunable takes a value in the range [0, 100] with a default value of
 20. This tunable determines how aggressively compaction is done in the
 background. Write of a non zero value to this tunable will immediately
 trigger the proactive compaction. Setting it to 0 disables proactive compaction.
 
 Note that compaction has a non-trivial system-wide impact as pages
 belonging to different processes are moved around, which could also lead
 to latency spikes in unsuspecting applications. The kernel employs
 various heuristics to avoid wasting CPU cycles if it detects that
 proactive compaction is not being effective.
 
 Be careful when setting it to extreme values like 100, as that may
 cause excessive background compaction activity.
 
 compact_unevictable_allowed
 ===========================
 
 Available only when CONFIG_COMPACTION is set. When set to 1, compaction is
 allowed to examine the unevictable lru (mlocked pages) for pages to compact.
 This should be used on systems where stalls for minor page faults are an
 acceptable trade for large contiguous free memory.  Set to 0 to prevent
 compaction from moving pages that are unevictable.  Default value is 1.
 On CONFIG_PREEMPT_RT the default value is 0 in order to avoid a page fault, due
 to compaction, which would block the task from becoming active until the fault
 is resolved.
 
 
 dirty_background_bytes
 ======================
 
 Contains the amount of dirty memory at which the background kernel
 flusher threads will start writeback.
 
 Note:
   dirty_background_bytes is the counterpart of dirty_background_ratio. Only
   one of them may be specified at a time. When one sysctl is written it is
   immediately taken into account to evaluate the dirty memory limits and the
   other appears as 0 when read.
 
 
 dirty_background_ratio
 ======================
 
 Contains, as a percentage of total available memory that contains free pages
 and reclaimable pages, the number of pages at which the background kernel
 flusher threads will start writing out dirty data.
 
 The total available memory is not equal to total system memory.
 
 
 dirty_bytes
 ===========
 
 Contains the amount of dirty memory at which a process generating disk writes
 will itself start writeback.
 
 Note: dirty_bytes is the counterpart of dirty_ratio. Only one of them may be
 specified at a time. When one sysctl is written it is immediately taken into
 account to evaluate the dirty memory limits and the other appears as 0 when
 read.
 
 Note: the minimum value allowed for dirty_bytes is two pages (in bytes); any
 value lower than this limit will be ignored and the old configuration will be
 retained.
 
 
 dirty_expire_centisecs
 ======================
 
 This tunable is used to define when dirty data is old enough to be eligible
 for writeout by the kernel flusher threads.  It is expressed in 100'ths
 of a second.  Data which has been dirty in-memory for longer than this
 interval will be written out next time a flusher thread wakes up.
 
 
 dirty_ratio
 ===========
 
 Contains, as a percentage of total available memory that contains free pages
 and reclaimable pages, the number of pages at which a process which is
 generating disk writes will itself start writing out dirty data.
 
 The total available memory is not equal to total system memory.
 
 
 dirtytime_expire_seconds
 ========================
 
 When a lazytime inode is constantly having its pages dirtied, the inode with
 an updated timestamp will never get chance to be written out.  And, if the
 only thing that has happened on the file system is a dirtytime inode caused
 by an atime update, a worker will be scheduled to make sure that inode
 eventually gets pushed out to disk.  This tunable is used to define when dirty
 inode is old enough to be eligible for writeback by the kernel flusher threads.
 And, it is also used as the interval to wakeup dirtytime_writeback thread.
 
 
 dirty_writeback_centisecs
 =========================
 
 The kernel flusher threads will periodically wake up and write `old` data
 out to disk.  This tunable expresses the interval between those wakeups, in
 100'ths of a second.
 
 Setting this to zero disables periodic writeback altogether.
 
 
 drop_caches
 ===========
 
 Writing to this will cause the kernel to drop clean caches, as well as
 reclaimable slab objects like dentries and inodes.  Once dropped, their
 memory becomes free.
 
 To free pagecache::
 
         echo 1 > /proc/sys/vm/drop_caches
 
 To free reclaimable slab objects (includes dentries and inodes)::
 
         echo 2 > /proc/sys/vm/drop_caches
 
 To free slab objects and pagecache::
 
         echo 3 > /proc/sys/vm/drop_caches
 
 This is a non-destructive operation and will not free any dirty objects.
 To increase the number of objects freed by this operation, the user may run
 `sync` prior to writing to /proc/sys/vm/drop_caches.  This will minimize the
 number of dirty objects on the system and create more candidates to be
 dropped.
 
 This file is not a means to control the growth of the various kernel caches
 (inodes, dentries, pagecache, etc...)  These objects are automatically
 reclaimed by the kernel when memory is needed elsewhere on the system.
 
 Use of this file can cause performance problems.  Since it discards cached
 objects, it may cost a significant amount of I/O and CPU to recreate the
 dropped objects, especially if they were under heavy use.  Because of this,
 use outside of a testing or debugging environment is not recommended.
 
 You may see informational messages in your kernel log when this file is
 used::
 
         cat (1234): drop_caches: 3
 
 These are informational only.  They do not mean that anything is wrong
 with your system.  To disable them, echo 4 (bit 2) into drop_caches.
 
 
 extfrag_threshold
 =================
 
 This parameter affects whether the kernel will compact memory or direct
 reclaim to satisfy a high-order allocation. The extfrag/extfrag_index file in
 debugfs shows what the fragmentation index for each order is in each zone in
 the system. Values tending towards 0 imply allocations would fail due to lack
 of memory, values towards 1000 imply failures are due to fragmentation and -1
 implies that the allocation will succeed as long as watermarks are met.
 
 The kernel will not compact memory in a zone if the
 fragmentation index is <= extfrag_threshold. The default value is 500.
 
 
 highmem_is_dirtyable
 ====================
 
 Available only for systems with CONFIG_HIGHMEM enabled (32b systems).
 
 This parameter controls whether the high memory is considered for dirty
 writers throttling.  This is not the case by default which means that
 only the amount of memory directly visible/usable by the kernel can
 be dirtied. As a result, on systems with a large amount of memory and
 lowmem basically depleted writers might be throttled too early and
 streaming writes can get very slow.
 
 Changing the value to non zero would allow more memory to be dirtied
 and thus allow writers to write more data which can be flushed to the
 storage more effectively. Note this also comes with a risk of pre-mature
 OOM killer because some writers (e.g. direct block device writes) can
 only use the low memory and they can fill it up with dirty data without
 any throttling.
 
 
 hugetlb_shm_group
 =================
 
 hugetlb_shm_group contains group id that is allowed to create SysV
 shared memory segment using hugetlb page.
 
 
 laptop_mode
 ===========
 
 laptop_mode is a knob that controls "laptop mode". All the things that are
 controlled by this knob are discussed in Documentation/admin-guide/laptops/laptop-mode.rst.
 
 
 legacy_va_layout
 ================
 
 If non-zero, this sysctl disables the new 32-bit mmap layout - the kernel
 will use the legacy (2.4) layout for all processes.
 
 
 lowmem_reserve_ratio
 ====================
 
 For some specialised workloads on highmem machines it is dangerous for
 the kernel to allow process memory to be allocated from the "lowmem"
 zone.  This is because that memory could then be pinned via the mlock()
 system call, or by unavailability of swapspace.
 
 And on large highmem machines this lack of reclaimable lowmem memory
 can be fatal.
 
 So the Linux page allocator has a mechanism which prevents allocations
 which *could* use highmem from using too much lowmem.  This means that
 a certain amount of lowmem is defended from the possibility of being
 captured into pinned user memory.
 
 (The same argument applies to the old 16 megabyte ISA DMA region.  This
 mechanism will also defend that region from allocations which could use
 highmem or lowmem).
 
 The `lowmem_reserve_ratio` tunable determines how aggressive the kernel is
 in defending these lower zones.
 
 If you have a machine which uses highmem or ISA DMA and your
 applications are using mlock(), or if you are running with no swap then
 you probably should change the lowmem_reserve_ratio setting.
 
 The lowmem_reserve_ratio is an array. You can see them by reading this file::
 
         % cat /proc/sys/vm/lowmem_reserve_ratio
         256     256     32
 
 But, these values are not used directly. The kernel calculates # of protection
 pages for each zones from them. These are shown as array of protection pages
 in /proc/zoneinfo like followings. (This is an example of x86-64 box).
 Each zone has an array of protection pages like this::
 
   Node 0, zone      DMA
     pages free     1355
           min      3
           low      3
           high     4
         :
         :
       numa_other   0
           protection: (0, 2004, 2004, 2004)
         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
     pagesets
       cpu: 0 pcp: 0
           :
 
 These protections are added to score to judge whether this zone should be used
 for page allocation or should be reclaimed.
 
 In this example, if normal pages (index=2) are required to this DMA zone and
 watermark[WMARK_HIGH] is used for watermark, the kernel judges this zone should
 not be used because pages_free(1355) is smaller than watermark + protection[2]
 (4 + 2004 = 2008). If this protection value is 0, this zone would be used for
 normal page requirement. If requirement is DMA zone(index=0), protection[0]
 (=0) is used.
 
 zone[i]'s protection[j] is calculated by following expression::
 
   (i < j):
     zone[i]->protection[j]
     = (total sums of managed_pages from zone[i+1] to zone[j] on the node)
       / lowmem_reserve_ratio[i];
   (i = j):
      (should not be protected. = 0;
   (i > j):
      (not necessary, but looks 0)
 
 The default values of lowmem_reserve_ratio[i] are
 
     === ====================================
     256 (if zone[i] means DMA or DMA32 zone)
     32  (others)
     === ====================================
 
 As above expression, they are reciprocal number of ratio.
 256 means 1/256. # of protection pages becomes about "0.39%" of total managed
 pages of higher zones on the node.
 
 If you would like to protect more pages, smaller values are effective.
 The minimum value is 1 (1/1 -> 100%). The value less than 1 completely
 disables protection of the pages.
 
 
 max_map_count:
 ==============
 
 This file contains the maximum number of memory map areas a process
 may have. Memory map areas are used as a side-effect of calling
 malloc, directly by mmap, mprotect, and madvise, and also when loading
 shared libraries.
 
 While most applications need less than a thousand maps, certain
 programs, particularly malloc debuggers, may consume lots of them,
 e.g., up to one or two maps per allocation.
 
 The default value is 65530.
 
 
 memory_failure_early_kill:
 ==========================
 
 Control how to kill processes when uncorrected memory error (typically
 a 2bit error in a memory module) is detected in the background by hardware
 that cannot be handled by the kernel. In some cases (like the page
 still having a valid copy on disk) the kernel will handle the failure
 transparently without affecting any applications. But if there is
 no other uptodate copy of the data it will kill to prevent any data
 corruptions from propagating.
 
 1: Kill all processes that have the corrupted and not reloadable page mapped
 as soon as the corruption is detected.  Note this is not supported
 for a few types of pages, like kernel internally allocated data or
 the swap cache, but works for the majority of user pages.
 
 0: Only unmap the corrupted page from all processes and only kill a process
 who tries to access it.
 
 The kill is done using a catchable SIGBUS with BUS_MCEERR_AO, so processes can
 handle this if they want to.
 
 This is only active on architectures/platforms with advanced machine
 check handling and depends on the hardware capabilities.
 
 Applications can override this setting individually with the PR_MCE_KILL prctl
 
 
 memory_failure_recovery
 =======================
 
 Enable memory failure recovery (when supported by the platform)
 
 1: Attempt recovery.
 
 0: Always panic on a memory failure.
 
 
 min_free_kbytes
 ===============
 
 This is used to force the Linux VM to keep a minimum number
 of kilobytes free.  The VM uses this number to compute a
 watermark[WMARK_MIN] value for each lowmem zone in the system.
 Each lowmem zone gets a number of reserved free pages based
 proportionally on its size.
 
 Some minimal amount of memory is needed to satisfy PF_MEMALLOC
 allocations; if you set this to lower than 1024KB, your system will
 become subtly broken, and prone to deadlock under high loads.
 
 Setting this too high will OOM your machine instantly.
 
 
 min_slab_ratio
 ==============
 
 This is available only on NUMA kernels.
 
 A percentage of the total pages in each zone.  On Zone reclaim
 (fallback from the local zone occurs) slabs will be reclaimed if more
 than this percentage of pages in a zone are reclaimable slab pages.
 This insures that the slab growth stays under control even in NUMA
 systems that rarely perform global reclaim.
 
 The default is 5 percent.
 
 Note that slab reclaim is triggered in a per zone / node fashion.
 The process of reclaiming slab memory is currently not node specific
 and may not be fast.
 
 
 min_unmapped_ratio
 ==================
 
 This is available only on NUMA kernels.
 
 This is a percentage of the total pages in each zone. Zone reclaim will
 only occur if more than this percentage of pages are in a state that
 zone_reclaim_mode allows to be reclaimed.
 
 If zone_reclaim_mode has the value 4 OR'd, then the percentage is compared
 against all file-backed unmapped pages including swapcache pages and tmpfs
 files. Otherwise, only unmapped pages backed by normal files but not tmpfs
 files and similar are considered.
 
 The default is 1 percent.
 
 
 mmap_min_addr
 =============
 
 This file indicates the amount of address space  which a user process will
 be restricted from mmapping.  Since kernel null dereference bugs could
 accidentally operate based on the information in the first couple of pages
 of memory userspace processes should not be allowed to write to them.  By
 default this value is set to 0 and no protections will be enforced by the
 security module.  Setting this value to something like 64k will allow the
 vast majority of applications to work correctly and provide defense in depth
 against future potential kernel bugs.
 
 
 mmap_rnd_bits
 =============
 
 This value can be used to select the number of bits to use to
 determine the random offset to the base address of vma regions
 resulting from mmap allocations on architectures which support
 tuning address space randomization.  This value will be bounded
 by the architecture's minimum and maximum supported values.
 
 This value can be changed after boot using the
 /proc/sys/vm/mmap_rnd_bits tunable
 
 
 mmap_rnd_compat_bits
 ====================
 
 This value can be used to select the number of bits to use to
 determine the random offset to the base address of vma regions
 resulting from mmap allocations for applications run in
 compatibility mode on architectures which support tuning address
 space randomization.  This value will be bounded by the
 architecture's minimum and maximum supported values.
 
 This value can be changed after boot using the
 /proc/sys/vm/mmap_rnd_compat_bits tunable
 
 
 nr_hugepages
 ============
 
 Change the minimum size of the hugepage pool.
 
 See Documentation/admin-guide/mm/hugetlbpage.rst
 
 
 hugetlb_optimize_vmemmap
 ========================
 
 This knob is not available when the size of 'struct page' (a structure defined
 in include/linux/mm_types.h) is not power of two (an unusual system config could
 result in this).
 
 Enable (set to 1) or disable (set to 0) HugeTLB Vmemmap Optimization (HVO).
 
 Once enabled, the vmemmap pages of subsequent allocation of HugeTLB pages from
 buddy allocator will be optimized (7 pages per 2MB HugeTLB page and 4095 pages
 per 1GB HugeTLB page), whereas already allocated HugeTLB pages will not be
 optimized.  When those optimized HugeTLB pages are freed from the HugeTLB pool
 to the buddy allocator, the vmemmap pages representing that range needs to be
 remapped again and the vmemmap pages discarded earlier need to be rellocated
 again.  If your use case is that HugeTLB pages are allocated 'on the fly' (e.g.
 never explicitly allocating HugeTLB pages with 'nr_hugepages' but only set
 'nr_overcommit_hugepages', those overcommitted HugeTLB pages are allocated 'on
 the fly') instead of being pulled from the HugeTLB pool, you should weigh the
 benefits of memory savings against the more overhead (~2x slower than before)
 of allocation or freeing HugeTLB pages between the HugeTLB pool and the buddy
 allocator.  Another behavior to note is that if the system is under heavy memory
 pressure, it could prevent the user from freeing HugeTLB pages from the HugeTLB
 pool to the buddy allocator since the allocation of vmemmap pages could be
 failed, you have to retry later if your system encounter this situation.
 
 Once disabled, the vmemmap pages of subsequent allocation of HugeTLB pages from
 buddy allocator will not be optimized meaning the extra overhead at allocation
 time from buddy allocator disappears, whereas already optimized HugeTLB pages
 will not be affected.  If you want to make sure there are no optimized HugeTLB
 pages, you can set "nr_hugepages" to 0 first and then disable this.  Note that
 writing 0 to nr_hugepages will make any "in use" HugeTLB pages become surplus
 pages.  So, those surplus pages are still optimized until they are no longer
 in use.  You would need to wait for those surplus pages to be released before
 there are no optimized pages in the system.
 
 
 nr_hugepages_mempolicy
 ======================
 
 Change the size of the hugepage pool at run-time on a specific
 set of NUMA nodes.
 
 See Documentation/admin-guide/mm/hugetlbpage.rst
 
 
 nr_overcommit_hugepages
 =======================
 
 Change the maximum size of the hugepage pool. The maximum is
 nr_hugepages + nr_overcommit_hugepages.
 
 See Documentation/admin-guide/mm/hugetlbpage.rst
 
 
 nr_trim_pages
 =============
 
 This is available only on NOMMU kernels.
 
 This value adjusts the excess page trimming behaviour of power-of-2 aligned
 NOMMU mmap allocations.
 
 A value of 0 disables trimming of allocations entirely, while a value of 1
 trims excess pages aggressively. Any value >= 1 acts as the watermark where
 trimming of allocations is initiated.
 
 The default value is 1.
 
 See Documentation/admin-guide/mm/nommu-mmap.rst for more information.
 
 
 numa_zonelist_order
 ===================
 
 This sysctl is only for NUMA and it is deprecated. Anything but
 Node order will fail!
 
 'where the memory is allocated from' is controlled by zonelists.
 
 (This documentation ignores ZONE_HIGHMEM/ZONE_DMA32 for simple explanation.
 you may be able to read ZONE_DMA as ZONE_DMA32...)
 
 In non-NUMA case, a zonelist for GFP_KERNEL is ordered as following.
 ZONE_NORMAL -> ZONE_DMA
 This means that a memory allocation request for GFP_KERNEL will
 get memory from ZONE_DMA only when ZONE_NORMAL is not available.
 
 In NUMA case, you can think of following 2 types of order.
 Assume 2 node NUMA and below is zonelist of Node(0)'s GFP_KERNEL::
 
   (A) Node(0) ZONE_NORMAL -> Node(0) ZONE_DMA -> Node(1) ZONE_NORMAL
   (B) Node(0) ZONE_NORMAL -> Node(1) ZONE_NORMAL -> Node(0) ZONE_DMA.
 
 Type(A) offers the best locality for processes on Node(0), but ZONE_DMA
 will be used before ZONE_NORMAL exhaustion. This increases possibility of
 out-of-memory(OOM) of ZONE_DMA because ZONE_DMA is tend to be small.
 
 Type(B) cannot offer the best locality but is more robust against OOM of
 the DMA zone.
 
 Type(A) is called as "Node" order. Type (B) is "Zone" order.
 
 "Node order" orders the zonelists by node, then by zone within each node.
 Specify "[Nn]ode" for node order
 
 "Zone Order" orders the zonelists by zone type, then by node within each
 zone.  Specify "[Zz]one" for zone order.
 
 Specify "[Dd]efault" to request automatic configuration.
 
 On 32-bit, the Normal zone needs to be preserved for allocations accessible
 by the kernel, so "zone" order will be selected.
 
 On 64-bit, devices that require DMA32/DMA are relatively rare, so "node"
 order will be selected.
 
 Default order is recommended unless this is causing problems for your
 system/application.
 
 
 oom_dump_tasks
 ==============
 
 Enables a system-wide task dump (excluding kernel threads) to be produced
 when the kernel performs an OOM-killing and includes such information as
 pid, uid, tgid, vm size, rss, pgtables_bytes, swapents, oom_score_adj
 score, and name.  This is helpful to determine why the OOM killer was
 invoked, to identify the rogue task that caused it, and to determine why
 the OOM killer chose the task it did to kill.
 
 If this is set to zero, this information is suppressed.  On very
 large systems with thousands of tasks it may not be feasible to dump
 the memory state information for each one.  Such systems should not
 be forced to incur a performance penalty in OOM conditions when the
 information may not be desired.
 
 If this is set to non-zero, this information is shown whenever the
 OOM killer actually kills a memory-hogging task.
 
 The default value is 1 (enabled).
 
 
 oom_kill_allocating_task
 ========================
 
 This enables or disables killing the OOM-triggering task in
 out-of-memory situations.
 
 If this is set to zero, the OOM killer will scan through the entire
 tasklist and select a task based on heuristics to kill.  This normally
 selects a rogue memory-hogging task that frees up a large amount of
 memory when killed.
 
 If this is set to non-zero, the OOM killer simply kills the task that
 triggered the out-of-memory condition.  This avoids the expensive
 tasklist scan.
 
 If panic_on_oom is selected, it takes precedence over whatever value
 is used in oom_kill_allocating_task.
 
 The default value is 0.
 
 
 overcommit_kbytes
 =================
 
 When overcommit_memory is set to 2, the committed address space is not
 permitted to exceed swap plus this amount of physical RAM. See below.
 
 Note: overcommit_kbytes is the counterpart of overcommit_ratio. Only one
 of them may be specified at a time. Setting one disables the other (which
 then appears as 0 when read).
 
 
 overcommit_memory
 =================
 
 This value contains a flag that enables memory overcommitment.
 
 When this flag is 0, the kernel attempts to estimate the amount
 of free memory left when userspace requests more memory.
 
 When this flag is 1, the kernel pretends there is always enough
 memory until it actually runs out.
 
 When this flag is 2, the kernel uses a "never overcommit"
 policy that attempts to prevent any overcommit of memory.
 Note that user_reserve_kbytes affects this policy.
 
 This feature can be very useful because there are a lot of
 programs that malloc() huge amounts of memory "just-in-case"
 and don't use much of it.
 
 The default value is 0.
 
 See Documentation/mm/overcommit-accounting.rst and
 mm/util.c::__vm_enough_memory() for more information.
 
 
 overcommit_ratio
 ================
 
 When overcommit_memory is set to 2, the committed address
 space is not permitted to exceed swap plus this percentage
 of physical RAM.  See above.
 
 
 page-cluster
 ============
 
 page-cluster controls the number of pages up to which consecutive pages
 are read in from swap in a single attempt. This is the swap counterpart
 to page cache readahead.
 The mentioned consecutivity is not in terms of virtual/physical addresses,
 but consecutive on swap space - that means they were swapped out together.
 
 It is a logarithmic value - setting it to zero means "1 page", setting
 it to 1 means "2 pages", setting it to 2 means "4 pages", etc.
 Zero disables swap readahead completely.
 
 The default value is three (eight pages at a time).  There may be some
 small benefits in tuning this to a different value if your workload is
 swap-intensive.
 
 Lower values mean lower latencies for initial faults, but at the same time
 extra faults and I/O delays for following faults if they would have been part of
 that consecutive pages readahead would have brought in.
 
 
 page_lock_unfairness
 ====================
 
 This value determines the number of times that the page lock can be
 stolen from under a waiter. After the lock is stolen the number of times
 specified in this file (default is 5), the "fair lock handoff" semantics
 will apply, and the waiter will only be awakened if the lock can be taken.
 
 panic_on_oom
 ============
 
 This enables or disables panic on out-of-memory feature.
 
 If this is set to 0, the kernel will kill some rogue process,
 called oom_killer.  Usually, oom_killer can kill rogue processes and
 system will survive.
 
 If this is set to 1, the kernel panics when out-of-memory happens.
 However, if a process limits using nodes by mempolicy/cpusets,
 and those nodes become memory exhaustion status, one process
 may be killed by oom-killer. No panic occurs in this case.
 Because other nodes' memory may be free. This means system total status
 may be not fatal yet.
 
 If this is set to 2, the kernel panics compulsorily even on the
 above-mentioned. Even oom happens under memory cgroup, the whole
 system panics.
 
 The default value is 0.
 
 1 and 2 are for failover of clustering. Please select either
 according to your policy of failover.
 
 panic_on_oom=2+kdump gives you very strong tool to investigate
 why oom happens. You can get snapshot.
 
 
 percpu_pagelist_high_fraction
 =============================
 
 This is the fraction of pages in each zone that are can be stored to
 per-cpu page lists. It is an upper boundary that is divided depending
 on the number of online CPUs. The min value for this is 8 which means
 that we do not allow more than 1/8th of pages in each zone to be stored
 on per-cpu page lists. This entry only changes the value of hot per-cpu
 page lists. A user can specify a number like 100 to allocate 1/100th of
 each zone between per-cpu lists.
 
 The batch value of each per-cpu page list remains the same regardless of
 the value of the high fraction so allocation latencies are unaffected.
 
 The initial value is zero. Kernel uses this value to set the high pcp->high
 mark based on the low watermark for the zone and the number of local
 online CPUs.  If the user writes '0' to this sysctl, it will revert to
 this default behavior.
 
 
 stat_interval
 =============
 
 The time interval between which vm statistics are updated.  The default
 is 1 second.
 
 
 stat_refresh
 ============
 
 Any read or write (by root only) flushes all the per-cpu vm statistics
 into their global totals, for more accurate reports when testing
 e.g. cat /proc/sys/vm/stat_refresh /proc/meminfo
 
 As a side-effect, it also checks for negative totals (elsewhere reported
 as 0) and "fails" with EINVAL if any are found, with a warning in dmesg.
 (At time of writing, a few stats are known sometimes to be found negative,
 with no ill effects: errors and warnings on these stats are suppressed.)
 
 
 numa_stat
 =========
 
 This interface allows runtime configuration of numa statistics.
 
 When page allocation performance becomes a bottleneck and you can tolerate
 some possible tool breakage and decreased numa counter precision, you can
 do::
 
         echo 0 > /proc/sys/vm/numa_stat
 
 When page allocation performance is not a bottleneck and you want all
 tooling to work, you can do::
 
         echo 1 > /proc/sys/vm/numa_stat
 
 
 swappiness
 ==========
 
 This control is used to define the rough relative IO cost of swapping
 and filesystem paging, as a value between 0 and 200. At 100, the VM
 assumes equal IO cost and will thus apply memory pressure to the page
 cache and swap-backed pages equally; lower values signify more
 expensive swap IO, higher values indicates cheaper.
 
 Keep in mind that filesystem IO patterns under memory pressure tend to
 be more efficient than swap's random IO. An optimal value will require
 experimentation and will also be workload-dependent.
 
 The default value is 60.
 
 For in-memory swap, like zram or zswap, as well as hybrid setups that
 have swap on faster devices than the filesystem, values beyond 100 can
 be considered. For example, if the random IO against the swap device
 is on average 2x faster than IO from the filesystem, swappiness should
 be 133 (x + 2x = 200, 2x = 133.33).
 
 At 0, the kernel will not initiate swap until the amount of free and
 file-backed pages is less than the high watermark in a zone.
 
 
 unprivileged_userfaultfd
 ========================
 
 This flag controls the mode in which unprivileged users can use the
 userfaultfd system calls. Set this to 0 to restrict unprivileged users
 to handle page faults in user mode only. In this case, users without
 SYS_CAP_PTRACE must pass UFFD_USER_MODE_ONLY in order for userfaultfd to
 succeed. Prohibiting use of userfaultfd for handling faults from kernel
 mode may make certain vulnerabilities more difficult to exploit.
 
 Set this to 1 to allow unprivileged users to use the userfaultfd system
 calls without any restrictions.
 
 The default value is 0.
 
 
 user_reserve_kbytes
 ===================
 
 When overcommit_memory is set to 2, "never overcommit" mode, reserve
 min(3% of current process size, user_reserve_kbytes) of free memory.
 This is intended to prevent a user from starting a single memory hogging
 process, such that they cannot recover (kill the hog).
 
 user_reserve_kbytes defaults to min(3% of the current process size, 128MB).
 
 If this is reduced to zero, then the user will be allowed to allocate
 all free memory with a single process, minus admin_reserve_kbytes.
 Any subsequent attempts to execute a command will result in
 "fork: Cannot allocate memory".
 
 Changing this takes effect whenever an application requests memory.
 
 
 vfs_cache_pressure
 ==================
 
 This percentage value controls the tendency of the kernel to reclaim
 the memory which is used for caching of directory and inode objects.
 
 At the default value of vfs_cache_pressure=100 the kernel will attempt to
 reclaim dentries and inodes at a "fair" rate with respect to pagecache and
 swapcache reclaim.  Decreasing vfs_cache_pressure causes the kernel to prefer
 to retain dentry and inode caches. When vfs_cache_pressure=0, the kernel will
 never reclaim dentries and inodes due to memory pressure and this can easily
 lead to out-of-memory conditions. Increasing vfs_cache_pressure beyond 100
 causes the kernel to prefer to reclaim dentries and inodes.
 
 Increasing vfs_cache_pressure significantly beyond 100 may have negative
 performance impact. Reclaim code needs to take various locks to find freeable
 directory and inode objects. With vfs_cache_pressure=1000, it will look for
 ten times more freeable objects than there are.
 
 
 watermark_boost_factor
 ======================
 
 This factor controls the level of reclaim when memory is being fragmented.
 It defines the percentage of the high watermark of a zone that will be
 reclaimed if pages of different mobility are being mixed within pageblocks.
 The intent is that compaction has less work to do in the future and to
 increase the success rate of future high-order allocations such as SLUB
 allocations, THP and hugetlbfs pages.
 
 To make it sensible with respect to the watermark_scale_factor
 parameter, the unit is in fractions of 10,000. The default value of
 15,000 means that up to 150% of the high watermark will be reclaimed in the
 event of a pageblock being mixed due to fragmentation. The level of reclaim
 is determined by the number of fragmentation events that occurred in the
 recent past. If this value is smaller than a pageblock then a pageblocks
 worth of pages will be reclaimed (e.g.  2MB on 64-bit x86). A boost factor
 of 0 will disable the feature.
 
 
 watermark_scale_factor
 ======================
 
 This factor controls the aggressiveness of kswapd. It defines the
 amount of memory left in a node/system before kswapd is woken up and
 how much memory needs to be free before kswapd goes back to sleep.
 
 The unit is in fractions of 10,000. The default value of 10 means the
 distances between watermarks are 0.1% of the available memory in the
 node/system. The maximum value is 3000, or 30% of memory.
 
 A high rate of threads entering direct reclaim (allocstall) or kswapd
 going to sleep prematurely (kswapd_low_wmark_hit_quickly) can indicate
 that the number of free pages kswapd maintains for latency reasons is
 too small for the allocation bursts occurring in the system. This knob
 can then be used to tune kswapd aggressiveness accordingly.
 
 
 zone_reclaim_mode
 =================
 
 Zone_reclaim_mode allows someone to set more or less aggressive approaches to
 reclaim memory when a zone runs out of memory. If it is set to zero then no
 zone reclaim occurs. Allocations will be satisfied from other zones / nodes
 in the system.
 
 This is value OR'ed together of
 
 =       ===================================
 1       Zone reclaim on
 2       Zone reclaim writes dirty pages out
 4       Zone reclaim swaps pages
 =       ===================================
 
 zone_reclaim_mode is disabled by default.  For file servers or workloads
 that benefit from having their data cached, zone_reclaim_mode should be
 left disabled as the caching effect is likely to be more important than
 data locality.
 
 Consider enabling one or more zone_reclaim mode bits if it's known that the
 workload is partitioned such that each partition fits within a NUMA node
 and that accessing remote memory would cause a measurable performance
 reduction.  The page allocator will take additional actions before
 allocating off node pages.
 
 Allowing zone reclaim to write out pages stops processes that are
 writing large amounts of data from dirtying pages on other nodes. Zone
 reclaim will write out dirty pages if a zone fills up and so effectively
 throttle the process. This may decrease the performance of a single process
 since it cannot use all of system memory to buffer the outgoing writes
 anymore but it preserve the memory on other nodes so that the performance
 of other processes running on other nodes will not be affected.
 
 Allowing regular swap effectively restricts allocations to the local
 node unless explicitly overridden by memory policies or cpuset
 configurations.

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