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authorChuck Ebbert <76306.1226@compuserve.com>2005-09-09 13:10:15 -0700
committerLinus Torvalds <torvalds@g5.osdl.org>2005-09-09 14:03:43 -0700
commitaf97c7220a0376beed827e72e3bb27731af7109d (patch)
treedae9462270cf9345184b23c95fedbe0fb414514b /Documentation/filesystems
parentddb99f3d35b178f0715aab2f9d9ab25f61814347 (diff)
[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>
Diffstat (limited to 'Documentation/filesystems')
-rw-r--r--Documentation/filesystems/proc.txt42
1 files changed, 32 insertions, 10 deletions
diff --git a/Documentation/filesystems/proc.txt b/Documentation/filesystems/proc.txt
index 5024ba7a592..d4773565ea2 100644
--- 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
----------------------------------