Pull ia64-mutex-primitives into release branch

[linux-2.6] / Documentation / filesystems / proc.txt

diff --git a/Documentation/filesystems/proc.txt b/Documentation/filesystems/proc.txt
index 5024ba7..944cf10 100644 (file)
--- a/Documentation/filesystems/proc.txt
+++ b/Documentation/filesystems/proc.txt
@@ -418,7 +418,7 @@ VmallocChunk:   111088 kB
        Dirty: Memory which is waiting to get written back to the disk
    Writeback: Memory which is actively being written back to the disk
       Mapped: files which have been mmaped, such as libraries
-              Slab: in-kernel data structures cache
+        Slab: in-kernel data structures cache
  CommitLimit: Based on the overcommit ratio ('vm.overcommit_ratio'),
               this is the total amount of  memory currently available to
               be allocated on the system. This limit is only adhered to
@@ -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
 ----------------------------------
@@ -1280,6 +1302,23 @@ VM has token based thrashing control mechanism and uses the token to prevent
 unnecessary page faults in thrashing situation. The unit of the value is
 second. The value would be useful to tune thrashing behavior.
 
+drop_caches
+-----------
+
+Writing to this will cause the kernel to drop clean caches, dentries and
+inodes from memory, causing that memory to become free.
+
+To free pagecache:
+       echo 1 > /proc/sys/vm/drop_caches
+To free dentries and inodes:
+       echo 2 > /proc/sys/vm/drop_caches
+To free pagecache, dentries and inodes:
+       echo 3 > /proc/sys/vm/drop_caches
+
+As this is a non-destructive operation and dirty objects are not freeable, the
+user should run `sync' first.
+
+
 2.5 /proc/sys/dev - Device specific parameters
 ----------------------------------------------