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[PATCH] docs: fix misinformation about overcommit_memory

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Someone complained about the docs for vm_overcommit_memory being wrong.
This patch copies the text from the vm documentation into procfs.

Signed-off-by: Chuck Ebbert <76306.1226@compuserve.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
This commit is contained in:
Chuck Ebbert 2005-09-09 13:10:15 -07:00 committed by Linus Torvalds
parent ddb99f3d35
commit af97c7220a
1 changed files with 31 additions and 9 deletions
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40
Documentation/filesystems/proc.txt
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@ -1241,16 +1241,38 @@ swap-intensive.
overcommit_memory
-----------------
This file contains one value. The following algorithm is used to decide if
there's enough memory: if the value of overcommit_memory is positive, then
there's always enough memory. This is a useful feature, since programs often
malloc() huge amounts of memory 'just in case', while they only use a small
part of it. Leaving this value at 0 will lead to the failure of such a huge
malloc(), when in fact the system has enough memory for the program to run.
Controls overcommit of system memory, possibly allowing processes
to allocate (but not use) more memory than is actually available.
On the other hand, enabling this feature can cause you to run out of memory
and thrash the system to death, so large and/or important servers will want to
set this value to 0.
0 - Heuristic overcommit handling. Obvious overcommits of
address space are refused. Used for a typical system. It
ensures a seriously wild allocation fails while allowing
overcommit to reduce swap usage. root is allowed to
allocate slighly more memory in this mode. This is the
default.
1 - Always overcommit. Appropriate for some scientific
applications.
2 - Don't overcommit. The total address space commit
for the system is not permitted to exceed swap plus a
configurable percentage (default is 50) of physical RAM.
Depending on the percentage you use, in most situations
this means a process will not be killed while attempting
to use already-allocated memory but will receive errors
on memory allocation as appropriate.
overcommit_ratio
----------------
Percentage of physical memory size to include in overcommit calculations
(see above.)
Memory allocation limit = swapspace + physmem * (overcommit_ratio / 100)
swapspace = total size of all swap areas
physmem = size of physical memory in system
nr_hugepages and hugetlb_shm_group
----------------------------------