speed process startup by 7%

[John Reiser]

https://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=162797

The kernel's random placement of the vDSO page disrupts prelinking.
This happens to about 7% of the execve on x86 that use only libc.so.6,
and grows to more than 60% of the execve for KDE, Gnome, multimedia
or any application with many and/or large prelinked shared libraries.

The bugzilla 162797 contains a patch which reduces the cost to zero,
and offers the administrator more choices: current random vDSO,
vDSO one page below STACK_TOP, vDSO just below .text of main.
It could be extended to place vDSO just below .text of PT_INTERP
(ld-linux.so.2), which would keep some benefits of randomness
(namely, the randomness of prelinking) yet still avoid stepping
on prelinked shared libraries.  (Prelink policy leaves at least
one page between prelinked libs.)

Wouldn't you rather save 7% ?

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