tree dae9462270cf9345184b23c95fedbe0fb414514b
parent ddb99f3d35b178f0715aab2f9d9ab25f61814347
author Chuck Ebbert <[EMAIL PROTECTED]> Sat, 10 Sep 2005 03:10:15 -0700
committer Linus Torvalds <[EMAIL PROTECTED]> Sat, 10 Sep 2005 04:03:43 -0700

[PATCH] docs: fix misinformation about overcommit_memory

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 <[EMAIL PROTECTED]>
Signed-off-by: Andrew Morton <[EMAIL PROTECTED]>
Signed-off-by: Linus Torvalds <[EMAIL PROTECTED]>

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

diff --git a/Documentation/filesystems/proc.txt 
--- a/Documentation/filesystems/proc.txt
+++ b/Documentation/filesystems/proc.txt
@@ -1241,16 +1241,38 @@ 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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