Update of Documentation: vm.txt and proc.txt
Update Documentation/sysctl/vm.txt and Documentation/filesystems/proc.txt. More specifically, the section on /proc/sys/vm in Documentation/filesystems/proc.txt was removed and a link to Documentation/sysctl/vm.txt added. Most of the verbiage from proc.txt was simply moved in vm.txt, with new addtional text for "swappiness" and "stat_interval". Signed-off-by: Peter W Morreale <pmorreale@novell.com> Acked-by: Randy Dunlap <randy.dunlap@oracle.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Peter W Morreale
Linus Torvalds
Родитель
b5db0e3865
Коммит
db0fb1848a
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@ -1371,292 +1371,8 @@ auto_msgmni default value is 1.
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2.4 /proc/sys/vm - The virtual memory subsystem
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-----------------------------------------------
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The files in this directory can be used to tune the operation of the virtual
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memory (VM) subsystem of the Linux kernel.
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vfs_cache_pressure
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------------------
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Controls the tendency of the kernel to reclaim the memory which is used for
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caching of directory and inode objects.
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At the default value of vfs_cache_pressure=100 the kernel will attempt to
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reclaim dentries and inodes at a "fair" rate with respect to pagecache and
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swapcache reclaim. Decreasing vfs_cache_pressure causes the kernel to prefer
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to retain dentry and inode caches. Increasing vfs_cache_pressure beyond 100
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causes the kernel to prefer to reclaim dentries and inodes.
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dirty_background_bytes
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----------------------
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Contains the amount of dirty memory at which the pdflush background writeback
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daemon will start writeback.
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If dirty_background_bytes is written, dirty_background_ratio becomes a function
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of its value (dirty_background_bytes / the amount of dirtyable system memory).
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dirty_background_ratio
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----------------------
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Contains, as a percentage of the dirtyable system memory (free pages + mapped
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pages + file cache, not including locked pages and HugePages), the number of
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pages at which the pdflush background writeback daemon will start writing out
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dirty data.
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If dirty_background_ratio is written, dirty_background_bytes becomes a function
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of its value (dirty_background_ratio * the amount of dirtyable system memory).
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dirty_bytes
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-----------
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Contains the amount of dirty memory at which a process generating disk writes
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will itself start writeback.
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If dirty_bytes is written, dirty_ratio becomes a function of its value
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(dirty_bytes / the amount of dirtyable system memory).
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dirty_ratio
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-----------
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Contains, as a percentage of the dirtyable system memory (free pages + mapped
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pages + file cache, not including locked pages and HugePages), the number of
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pages at which a process which is generating disk writes will itself start
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writing out dirty data.
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If dirty_ratio is written, dirty_bytes becomes a function of its value
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(dirty_ratio * the amount of dirtyable system memory).
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dirty_writeback_centisecs
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-------------------------
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The pdflush writeback daemons will periodically wake up and write `old' data
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out to disk. This tunable expresses the interval between those wakeups, in
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100'ths of a second.
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Setting this to zero disables periodic writeback altogether.
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dirty_expire_centisecs
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----------------------
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This tunable is used to define when dirty data is old enough to be eligible
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for writeout by the pdflush daemons. It is expressed in 100'ths of a second.
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Data which has been dirty in-memory for longer than this interval will be
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written out next time a pdflush daemon wakes up.
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highmem_is_dirtyable
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--------------------
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Only present if CONFIG_HIGHMEM is set.
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This defaults to 0 (false), meaning that the ratios set above are calculated
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as a percentage of lowmem only. This protects against excessive scanning
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in page reclaim, swapping and general VM distress.
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Setting this to 1 can be useful on 32 bit machines where you want to make
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random changes within an MMAPed file that is larger than your available
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lowmem without causing large quantities of random IO. Is is safe if the
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behavior of all programs running on the machine is known and memory will
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not be otherwise stressed.
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legacy_va_layout
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----------------
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If non-zero, this sysctl disables the new 32-bit mmap mmap layout - the kernel
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will use the legacy (2.4) layout for all processes.
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lowmem_reserve_ratio
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---------------------
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For some specialised workloads on highmem machines it is dangerous for
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the kernel to allow process memory to be allocated from the "lowmem"
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zone. This is because that memory could then be pinned via the mlock()
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system call, or by unavailability of swapspace.
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And on large highmem machines this lack of reclaimable lowmem memory
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can be fatal.
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So the Linux page allocator has a mechanism which prevents allocations
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which _could_ use highmem from using too much lowmem. This means that
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a certain amount of lowmem is defended from the possibility of being
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captured into pinned user memory.
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(The same argument applies to the old 16 megabyte ISA DMA region. This
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mechanism will also defend that region from allocations which could use
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highmem or lowmem).
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The `lowmem_reserve_ratio' tunable determines how aggressive the kernel is
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in defending these lower zones.
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If you have a machine which uses highmem or ISA DMA and your
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applications are using mlock(), or if you are running with no swap then
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you probably should change the lowmem_reserve_ratio setting.
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The lowmem_reserve_ratio is an array. You can see them by reading this file.
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-
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% cat /proc/sys/vm/lowmem_reserve_ratio
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256 256 32
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-
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Note: # of this elements is one fewer than number of zones. Because the highest
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zone's value is not necessary for following calculation.
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But, these values are not used directly. The kernel calculates # of protection
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pages for each zones from them. These are shown as array of protection pages
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in /proc/zoneinfo like followings. (This is an example of x86-64 box).
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Each zone has an array of protection pages like this.
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-
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Node 0, zone DMA
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pages free 1355
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min 3
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low 3
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high 4
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:
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:
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numa_other 0
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protection: (0, 2004, 2004, 2004)
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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pagesets
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cpu: 0 pcp: 0
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:
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-
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These protections are added to score to judge whether this zone should be used
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for page allocation or should be reclaimed.
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In this example, if normal pages (index=2) are required to this DMA zone and
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pages_high is used for watermark, the kernel judges this zone should not be
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used because pages_free(1355) is smaller than watermark + protection[2]
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(4 + 2004 = 2008). If this protection value is 0, this zone would be used for
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normal page requirement. If requirement is DMA zone(index=0), protection[0]
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(=0) is used.
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zone[i]'s protection[j] is calculated by following expression.
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(i < j):
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zone[i]->protection[j]
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= (total sums of present_pages from zone[i+1] to zone[j] on the node)
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/ lowmem_reserve_ratio[i];
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(i = j):
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(should not be protected. = 0;
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(i > j):
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(not necessary, but looks 0)
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The default values of lowmem_reserve_ratio[i] are
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256 (if zone[i] means DMA or DMA32 zone)
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32 (others).
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As above expression, they are reciprocal number of ratio.
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256 means 1/256. # of protection pages becomes about "0.39%" of total present
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pages of higher zones on the node.
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If you would like to protect more pages, smaller values are effective.
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The minimum value is 1 (1/1 -> 100%).
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page-cluster
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------------
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page-cluster controls the number of pages which are written to swap in
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a single attempt. The swap I/O size.
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It is a logarithmic value - setting it to zero means "1 page", setting
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it to 1 means "2 pages", setting it to 2 means "4 pages", etc.
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The default value is three (eight pages at a time). There may be some
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small benefits in tuning this to a different value if your workload is
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swap-intensive.
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overcommit_memory
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-----------------
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Controls overcommit of system memory, possibly allowing processes
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to allocate (but not use) more memory than is actually available.
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0 - Heuristic overcommit handling. Obvious overcommits of
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address space are refused. Used for a typical system. It
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ensures a seriously wild allocation fails while allowing
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overcommit to reduce swap usage. root is allowed to
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allocate slightly more memory in this mode. This is the
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default.
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1 - Always overcommit. Appropriate for some scientific
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applications.
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2 - Don't overcommit. The total address space commit
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for the system is not permitted to exceed swap plus a
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configurable percentage (default is 50) of physical RAM.
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Depending on the percentage you use, in most situations
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this means a process will not be killed while attempting
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to use already-allocated memory but will receive errors
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on memory allocation as appropriate.
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overcommit_ratio
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----------------
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Percentage of physical memory size to include in overcommit calculations
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(see above.)
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Memory allocation limit = swapspace + physmem * (overcommit_ratio / 100)
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swapspace = total size of all swap areas
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physmem = size of physical memory in system
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nr_hugepages and hugetlb_shm_group
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----------------------------------
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nr_hugepages configures number of hugetlb page reserved for the system.
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hugetlb_shm_group contains group id that is allowed to create SysV shared
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memory segment using hugetlb page.
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hugepages_treat_as_movable
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--------------------------
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This parameter is only useful when kernelcore= is specified at boot time to
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create ZONE_MOVABLE for pages that may be reclaimed or migrated. Huge pages
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are not movable so are not normally allocated from ZONE_MOVABLE. A non-zero
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value written to hugepages_treat_as_movable allows huge pages to be allocated
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from ZONE_MOVABLE.
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Once enabled, the ZONE_MOVABLE is treated as an area of memory the huge
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pages pool can easily grow or shrink within. Assuming that applications are
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not running that mlock() a lot of memory, it is likely the huge pages pool
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can grow to the size of ZONE_MOVABLE by repeatedly entering the desired value
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into nr_hugepages and triggering page reclaim.
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laptop_mode
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-----------
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laptop_mode is a knob that controls "laptop mode". All the things that are
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controlled by this knob are discussed in Documentation/laptops/laptop-mode.txt.
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block_dump
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----------
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block_dump enables block I/O debugging when set to a nonzero value. More
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information on block I/O debugging is in Documentation/laptops/laptop-mode.txt.
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swap_token_timeout
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------------------
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This file contains valid hold time of swap out protection token. The Linux
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VM has token based thrashing control mechanism and uses the token to prevent
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unnecessary page faults in thrashing situation. The unit of the value is
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second. The value would be useful to tune thrashing behavior.
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drop_caches
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-----------
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Writing to this will cause the kernel to drop clean caches, dentries and
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inodes from memory, causing that memory to become free.
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To free pagecache:
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echo 1 > /proc/sys/vm/drop_caches
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To free dentries and inodes:
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echo 2 > /proc/sys/vm/drop_caches
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To free pagecache, dentries and inodes:
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echo 3 > /proc/sys/vm/drop_caches
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As this is a non-destructive operation and dirty objects are not freeable, the
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user should run `sync' first.
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Please see: Documentation/sysctls/vm.txt for a description of these
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entries.
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2.5 /proc/sys/dev - Device specific parameters
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@ -1,12 +1,13 @@
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Documentation for /proc/sys/vm/* kernel version 2.2.10
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Documentation for /proc/sys/vm/* kernel version 2.6.29
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(c) 1998, 1999, Rik van Riel <riel@nl.linux.org>
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(c) 2008 Peter W. Morreale <pmorreale@novell.com>
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For general info and legal blurb, please look in README.
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==============================================================
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This file contains the documentation for the sysctl files in
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/proc/sys/vm and is valid for Linux kernel version 2.2.
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/proc/sys/vm and is valid for Linux kernel version 2.6.29.
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The files in this directory can be used to tune the operation
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of the virtual memory (VM) subsystem of the Linux kernel and
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@ -16,83 +17,244 @@ Default values and initialization routines for most of these
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files can be found in mm/swap.c.
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Currently, these files are in /proc/sys/vm:
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- overcommit_memory
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- page-cluster
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- dirty_ratio
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- block_dump
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- dirty_background_bytes
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- dirty_background_ratio
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- dirty_bytes
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- dirty_expire_centisecs
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- dirty_ratio
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- dirty_writeback_centisecs
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- highmem_is_dirtyable (only if CONFIG_HIGHMEM set)
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- drop_caches
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- hugepages_treat_as_movable
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- hugetlb_shm_group
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- laptop_mode
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- legacy_va_layout
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- lowmem_reserve_ratio
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- max_map_count
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- min_free_kbytes
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- laptop_mode
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- block_dump
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- drop-caches
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- zone_reclaim_mode
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- min_unmapped_ratio
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- min_slab_ratio
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- panic_on_oom
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- oom_dump_tasks
|
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- oom_kill_allocating_task
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- mmap_min_address
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- numa_zonelist_order
|
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- min_unmapped_ratio
|
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- mmap_min_addr
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- nr_hugepages
|
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- nr_overcommit_hugepages
|
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- nr_trim_pages (only if CONFIG_MMU=n)
|
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- nr_pdflush_threads
|
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- nr_trim_pages (only if CONFIG_MMU=n)
|
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- numa_zonelist_order
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- oom_dump_tasks
|
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- oom_kill_allocating_task
|
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- overcommit_memory
|
||||
- overcommit_ratio
|
||||
- page-cluster
|
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- panic_on_oom
|
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- percpu_pagelist_fraction
|
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- stat_interval
|
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- swappiness
|
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- vfs_cache_pressure
|
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- zone_reclaim_mode
|
||||
|
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|
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==============================================================
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|
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dirty_bytes, dirty_ratio, dirty_background_bytes,
|
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dirty_background_ratio, dirty_expire_centisecs,
|
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dirty_writeback_centisecs, highmem_is_dirtyable,
|
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vfs_cache_pressure, laptop_mode, block_dump, swap_token_timeout,
|
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drop-caches, hugepages_treat_as_movable:
|
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block_dump
|
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|
||||
See Documentation/filesystems/proc.txt
|
||||
block_dump enables block I/O debugging when set to a nonzero value. More
|
||||
information on block I/O debugging is in Documentation/laptops/laptop-mode.txt.
|
||||
|
||||
==============================================================
|
||||
|
||||
overcommit_memory:
|
||||
dirty_background_bytes
|
||||
|
||||
This value contains a flag that enables memory overcommitment.
|
||||
Contains the amount of dirty memory at which the pdflush background writeback
|
||||
daemon will start writeback.
|
||||
|
||||
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.
|
||||
|
||||
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/vm/overcommit-accounting and
|
||||
security/commoncap.c::cap_vm_enough_memory() for more information.
|
||||
If dirty_background_bytes is written, dirty_background_ratio becomes a function
|
||||
of its value (dirty_background_bytes / the amount of dirtyable system memory).
|
||||
|
||||
==============================================================
|
||||
|
||||
overcommit_ratio:
|
||||
dirty_background_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.
|
||||
Contains, as a percentage of total system memory, the number of pages at which
|
||||
the pdflush background writeback daemon will start writing out dirty data.
|
||||
|
||||
==============================================================
|
||||
|
||||
page-cluster:
|
||||
dirty_bytes
|
||||
|
||||
The Linux VM subsystem avoids excessive disk seeks by reading
|
||||
multiple pages on a page fault. The number of pages it reads
|
||||
is dependent on the amount of memory in your machine.
|
||||
Contains the amount of dirty memory at which a process generating disk writes
|
||||
will itself start writeback.
|
||||
|
||||
The number of pages the kernel reads in at once is equal to
|
||||
2 ^ page-cluster. Values above 2 ^ 5 don't make much sense
|
||||
for swap because we only cluster swap data in 32-page groups.
|
||||
If dirty_bytes is written, dirty_ratio becomes a function of its value
|
||||
(dirty_bytes / the amount of dirtyable system memory).
|
||||
|
||||
==============================================================
|
||||
|
||||
dirty_expire_centisecs
|
||||
|
||||
This tunable is used to define when dirty data is old enough to be eligible
|
||||
for writeout by the pdflush daemons. 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 pdflush daemon wakes up.
|
||||
|
||||
==============================================================
|
||||
|
||||
dirty_ratio
|
||||
|
||||
Contains, as a percentage of total system memory, the number of pages at which
|
||||
a process which is generating disk writes will itself start writing out dirty
|
||||
data.
|
||||
|
||||
==============================================================
|
||||
|
||||
dirty_writeback_centisecs
|
||||
|
||||
The pdflush writeback daemons 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, dentries and
|
||||
inodes from memory, causing that memory to become free.
|
||||
|
||||
To free pagecache:
|
||||
echo 1 > /proc/sys/vm/drop_caches
|
||||
To free dentries and inodes:
|
||||
echo 2 > /proc/sys/vm/drop_caches
|
||||
To free pagecache, dentries and inodes:
|
||||
echo 3 > /proc/sys/vm/drop_caches
|
||||
|
||||
As this is a non-destructive operation and dirty objects are not freeable, the
|
||||
user should run `sync' first.
|
||||
|
||||
==============================================================
|
||||
|
||||
hugepages_treat_as_movable
|
||||
|
||||
This parameter is only useful when kernelcore= is specified at boot time to
|
||||
create ZONE_MOVABLE for pages that may be reclaimed or migrated. Huge pages
|
||||
are not movable so are not normally allocated from ZONE_MOVABLE. A non-zero
|
||||
value written to hugepages_treat_as_movable allows huge pages to be allocated
|
||||
from ZONE_MOVABLE.
|
||||
|
||||
Once enabled, the ZONE_MOVABLE is treated as an area of memory the huge
|
||||
pages pool can easily grow or shrink within. Assuming that applications are
|
||||
not running that mlock() a lot of memory, it is likely the huge pages pool
|
||||
can grow to the size of ZONE_MOVABLE by repeatedly entering the desired value
|
||||
into nr_hugepages and triggering page reclaim.
|
||||
|
||||
==============================================================
|
||||
|
||||
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/laptops/laptop-mode.txt.
|
||||
|
||||
==============================================================
|
||||
|
||||
legacy_va_layout
|
||||
|
||||
If non-zero, this sysctl disables the new 32-bit mmap 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
|
||||
-
|
||||
Note: # of this elements is one fewer than number of zones. Because the highest
|
||||
zone's value is not necessary for following calculation.
|
||||
|
||||
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
|
||||
pages_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 present_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 present
|
||||
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%).
|
||||
|
||||
==============================================================
|
||||
|
||||
|
|
@ -113,9 +275,9 @@ The default value is 65536.
|
|||
|
||||
min_free_kbytes:
|
||||
|
||||
This is used to force the Linux VM to keep a minimum number
|
||||
This is used to force the Linux VM to keep a minimum number
|
||||
of kilobytes free. The VM uses this number to compute a pages_min
|
||||
value for each lowmem zone in the system. Each lowmem zone gets
|
||||
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
|
||||
|
|
@ -124,73 +286,6 @@ become subtly broken, and prone to deadlock under high loads.
|
|||
|
||||
Setting this too high will OOM your machine instantly.
|
||||
|
||||
==============================================================
|
||||
|
||||
percpu_pagelist_fraction
|
||||
|
||||
This is the fraction of pages at most (high mark pcp->high) in each zone that
|
||||
are allocated for each per cpu page list. The min value for this is 8. It
|
||||
means that we don't allow more than 1/8th of pages in each zone to be
|
||||
allocated in any single per_cpu_pagelist. This entry only changes the value
|
||||
of hot per cpu pagelists. User can specify a number like 100 to allocate
|
||||
1/100th of each zone to each per cpu page list.
|
||||
|
||||
The batch value of each per cpu pagelist is also updated as a result. It is
|
||||
set to pcp->high/4. The upper limit of batch is (PAGE_SHIFT * 8)
|
||||
|
||||
The initial value is zero. Kernel does not use this value at boot time to set
|
||||
the high water marks for each per cpu page list.
|
||||
|
||||
===============================================================
|
||||
|
||||
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 ORed together of
|
||||
|
||||
1 = Zone reclaim on
|
||||
2 = Zone reclaim writes dirty pages out
|
||||
4 = Zone reclaim swaps pages
|
||||
|
||||
zone_reclaim_mode is set during bootup to 1 if it is determined that pages
|
||||
from remote zones will cause a measurable performance reduction. The
|
||||
page allocator will then reclaim easily reusable pages (those page
|
||||
cache pages that are currently not used) before allocating off node pages.
|
||||
|
||||
It may be beneficial to switch off zone reclaim if the system is
|
||||
used for a file server and all of memory should be used for caching files
|
||||
from disk. In that case the caching effect is more important than
|
||||
data locality.
|
||||
|
||||
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.
|
||||
|
||||
=============================================================
|
||||
|
||||
min_unmapped_ratio:
|
||||
|
||||
This is available only on NUMA kernels.
|
||||
|
||||
A percentage of the total pages in each zone. Zone reclaim will only
|
||||
occur if more than this percentage of pages are file backed and unmapped.
|
||||
This is to insure that a minimal amount of local pages is still available for
|
||||
file I/O even if the node is overallocated.
|
||||
|
||||
The default is 1 percent.
|
||||
|
||||
=============================================================
|
||||
|
||||
min_slab_ratio:
|
||||
|
|
@ -211,69 +306,16 @@ and may not be fast.
|
|||
|
||||
=============================================================
|
||||
|
||||
panic_on_oom
|
||||
min_unmapped_ratio:
|
||||
|
||||
This enables or disables panic on out-of-memory feature.
|
||||
This is available only on NUMA kernels.
|
||||
|
||||
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.
|
||||
A percentage of the total pages in each zone. Zone reclaim will only
|
||||
occur if more than this percentage of pages are file backed and unmapped.
|
||||
This is to insure that a minimal amount of local pages is still available for
|
||||
file I/O even if the node is overallocated.
|
||||
|
||||
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.
|
||||
|
||||
The default value is 0.
|
||||
1 and 2 are for failover of clustering. Please select either
|
||||
according to your policy of failover.
|
||||
|
||||
=============================================================
|
||||
|
||||
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, cpu, oom_adj score, and
|
||||
name. This is helpful to determine why the OOM killer was invoked
|
||||
and to identify the rogue task that caused it.
|
||||
|
||||
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 0.
|
||||
|
||||
=============================================================
|
||||
|
||||
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.
|
||||
The default is 1 percent.
|
||||
|
||||
==============================================================
|
||||
|
||||
|
|
@ -290,6 +332,50 @@ against future potential kernel bugs.
|
|||
|
||||
==============================================================
|
||||
|
||||
nr_hugepages
|
||||
|
||||
Change the minimum size of the hugepage pool.
|
||||
|
||||
See Documentation/vm/hugetlbpage.txt
|
||||
|
||||
==============================================================
|
||||
|
||||
nr_overcommit_hugepages
|
||||
|
||||
Change the maximum size of the hugepage pool. The maximum is
|
||||
nr_hugepages + nr_overcommit_hugepages.
|
||||
|
||||
See Documentation/vm/hugetlbpage.txt
|
||||
|
||||
==============================================================
|
||||
|
||||
nr_pdflush_threads
|
||||
|
||||
The current number of pdflush threads. This value is read-only.
|
||||
The value changes according to the number of dirty pages in the system.
|
||||
|
||||
When neccessary, additional pdflush threads are created, one per second, up to
|
||||
nr_pdflush_threads_max.
|
||||
|
||||
==============================================================
|
||||
|
||||
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/nommu-mmap.txt for more information.
|
||||
|
||||
==============================================================
|
||||
|
||||
numa_zonelist_order
|
||||
|
||||
This sysctl is only for NUMA.
|
||||
|
|
@ -335,34 +421,199 @@ this is causing problems for your system/application.
|
|||
|
||||
==============================================================
|
||||
|
||||
nr_hugepages
|
||||
oom_dump_tasks
|
||||
|
||||
Change the minimum size of the hugepage pool.
|
||||
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, cpu, oom_adj score, and
|
||||
name. This is helpful to determine why the OOM killer was invoked
|
||||
and to identify the rogue task that caused it.
|
||||
|
||||
See Documentation/vm/hugetlbpage.txt
|
||||
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 0.
|
||||
|
||||
==============================================================
|
||||
|
||||
nr_overcommit_hugepages
|
||||
oom_kill_allocating_task
|
||||
|
||||
Change the maximum size of the hugepage pool. The maximum is
|
||||
nr_hugepages + nr_overcommit_hugepages.
|
||||
This enables or disables killing the OOM-triggering task in
|
||||
out-of-memory situations.
|
||||
|
||||
See Documentation/vm/hugetlbpage.txt
|
||||
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.
|
||||
|
||||
==============================================================
|
||||
|
||||
nr_trim_pages
|
||||
overcommit_memory:
|
||||
|
||||
This is available only on NOMMU kernels.
|
||||
This value contains a flag that enables memory overcommitment.
|
||||
|
||||
This value adjusts the excess page trimming behaviour of power-of-2 aligned
|
||||
NOMMU mmap allocations.
|
||||
When this flag is 0, the kernel attempts to estimate the amount
|
||||
of free memory left when userspace requests more memory.
|
||||
|
||||
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.
|
||||
When this flag is 1, the kernel pretends there is always enough
|
||||
memory until it actually runs out.
|
||||
|
||||
The default value is 1.
|
||||
When this flag is 2, the kernel uses a "never overcommit"
|
||||
policy that attempts to prevent any overcommit of memory.
|
||||
|
||||
See Documentation/nommu-mmap.txt for more information.
|
||||
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/vm/overcommit-accounting and
|
||||
security/commoncap.c::cap_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 which are written to swap in
|
||||
a single attempt. The swap I/O size.
|
||||
|
||||
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.
|
||||
|
||||
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.
|
||||
|
||||
=============================================================
|
||||
|
||||
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.
|
||||
|
||||
The default value is 0.
|
||||
1 and 2 are for failover of clustering. Please select either
|
||||
according to your policy of failover.
|
||||
|
||||
=============================================================
|
||||
|
||||
percpu_pagelist_fraction
|
||||
|
||||
This is the fraction of pages at most (high mark pcp->high) in each zone that
|
||||
are allocated for each per cpu page list. The min value for this is 8. It
|
||||
means that we don't allow more than 1/8th of pages in each zone to be
|
||||
allocated in any single per_cpu_pagelist. This entry only changes the value
|
||||
of hot per cpu pagelists. User can specify a number like 100 to allocate
|
||||
1/100th of each zone to each per cpu page list.
|
||||
|
||||
The batch value of each per cpu pagelist is also updated as a result. It is
|
||||
set to pcp->high/4. The upper limit of batch is (PAGE_SHIFT * 8)
|
||||
|
||||
The initial value is zero. Kernel does not use this value at boot time to set
|
||||
the high water marks for each per cpu page list.
|
||||
|
||||
==============================================================
|
||||
|
||||
stat_interval
|
||||
|
||||
The time interval between which vm statistics are updated. The default
|
||||
is 1 second.
|
||||
|
||||
==============================================================
|
||||
|
||||
swappiness
|
||||
|
||||
This control is used to define how aggressive the kernel will swap
|
||||
memory pages. Higher values will increase agressiveness, lower values
|
||||
descrease the amount of swap.
|
||||
|
||||
The default value is 60.
|
||||
|
||||
==============================================================
|
||||
|
||||
vfs_cache_pressure
|
||||
------------------
|
||||
|
||||
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. Increasing vfs_cache_pressure beyond 100
|
||||
causes the kernel to prefer to reclaim dentries and inodes.
|
||||
|
||||
==============================================================
|
||||
|
||||
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 ORed together of
|
||||
|
||||
1 = Zone reclaim on
|
||||
2 = Zone reclaim writes dirty pages out
|
||||
4 = Zone reclaim swaps pages
|
||||
|
||||
zone_reclaim_mode is set during bootup to 1 if it is determined that pages
|
||||
from remote zones will cause a measurable performance reduction. The
|
||||
page allocator will then reclaim easily reusable pages (those page
|
||||
cache pages that are currently not used) before allocating off node pages.
|
||||
|
||||
It may be beneficial to switch off zone reclaim if the system is
|
||||
used for a file server and all of memory should be used for caching files
|
||||
from disk. In that case the caching effect is more important than
|
||||
data locality.
|
||||
|
||||
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.
|
||||
|
||||
============ End of Document =================================
|
||||
|
|
|
|||
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