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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
parent
b5db0e3865
commit
db0fb1848a
2 changed files with 451 additions and 484 deletions
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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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