Re: [patch] mmap-speedup-2.5.42-C3

[Jakub Jelinek]

On Wed, Oct 16, 2002 at 10:03:52AM +0200, Ingo Molnar wrote:
> 
> On 15 Oct 2002, Andi Kleen wrote:
> 
> > When you oprofile KDE startup you notice that a lot of time is spent in
> > get_unmapped_area too. The reason is that every KDE process links with
> > 10-20 libraries and ends up with a 40-50 entry /proc/<pid>/maps.
> 
> actually, library mappings alone should not cause a slowdown, since we
> start the search at MAP_UNMAPPED_BASE and most library mappings are below
> 1GB. But if those libraries use mmap()-ed anonymous RAM that has different
> protections then the anonymous areas do not get merged and the scanning
> overhead goes up.

Libraries mapped by dynamic linker are mapped without MAP_FIXED and unless
you use prelinking, with 0 virtual address, ie. they all end up above 1GB.
And 99% of libraries uses different protections, for the read-only and
read-write segment.

	Jakub