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SubjectRe: [patch 2.6.13-rc6] docs: fix misinformation about overcommit_memory
On Fri, 19 Aug 2005 20:24:26 -0700, Andrew Morton wrote:

> Chuck Ebbert <> wrote:
> >
> > +Controls overcommit of system memory:
> It should explain what "overcommit" is.

Here is an improved version.

Signed-off-by: Chuck Ebbert <>

Documentation/filesystems/proc.txt | 42 ++++++++++++++++++++++++++++---------
1 files changed, 32 insertions(+), 10 deletions(-)

--- 2.6.13-rc6c.orig/Documentation/filesystems/proc.txt
+++ 2.6.13-rc6c/Documentation/filesystems/proc.txt
@@ -1240,16 +1240,38 @@ swap-intensive.

-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.
-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.
+Controls overcommit of system memory, possibly allowing processes
+to allocate (but not use) more memory than is actually available.
+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.
+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
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