overcommit memory - odz buffer

ref:http://www.kt.rim.or.jp/~kbk/zakkicho/09/zakkicho0905b.html#D20090517-5

Linux の Documentation/vm/overcommit-accounting をみれば分かりますが、まぁ glibc というより、Linux の仕様ですね。

The Linux kernel supports the following overcommit handling modes

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 + 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 accessing
                pages but will receive errors on memory allocation as
                appropriate.