[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 <76306.1226@compuserve.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

diff --git a/Documentation/filesystems/proc.txt b/Documentation/filesystems/proc.txt
index 5024ba7..d477356 100644 (file)
--- a/Documentation/filesystems/proc.txt
+++ b/Documentation/filesystems/proc.txt
@@ -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.
-
-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.
+
+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
 ----------------------------------