[PATCH] docs: fix misinformation about overcommit_memory

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

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