Speed up xubuntu by using more memory?

Eero Tamminen oak at helsinkinet.fi
Fri Sep 15 18:02:21 UTC 2006


On Friday 15 September 2006 15:30, Jelle de Jong wrote:
> I heard somewhere that big linux programs have to load and calculate and
> create links to library's every time they start. This is one of the
> reasons why openoffice is so slow.
> If it is possible to create a system that pre calculate these links and
> put them in a table that is loaded in the memory. It could be possible
> to speed up almost al linux programs especially the big ones.

That's prelink. What it does: it checks each (dynamic library) dependency
for a given binary, resolves the dynamically resolved symbols (like dynamic
linker does normally at run time when binary is loaded) and stores the
resolved addresses back to the binary on disk (to different section than the
symbol table I think).

If you update any of the binary dependencies, this prelinking needs to
be redone (dynamic linker will automatically skip the prelink information
if it's out of date).  You could add an apt-hook that (re-)does prelinking
when things are updated.

Besides improving application startup-time, prelinking will also save some
RAM because prelink information is read-only (i.e. can be discarded when 
memory is low and read back from disk if needed again) whereas run-time
resolved symbol addresses are naturally private to the process (i.e. can be
only written to swap when memory is low).  With a large number of large
(C++) library dependencies, the amount of memory needed for resolved symbols
can amount to several megabytes...

So, prelink will help if you:
- Have applications that link a lot of libraries: ldd <binary>|wc -l
  (several dozens)
- Those libraries export a lot of symbols: readelf -r <library>|wc -l
- are also running low on memory

Note that many of the applications, such as OpenOffice use dlopen() to load
parts of their functionality (plugins...) on-demand.  Because these
libraries cannot be known at linking/startup time, they cannot be given
fixed address and therefore won't be prelinked although rest/most of the
app would.  Michael Meeks (see Gnome performance-list) has some dynamic
linker / C-library patches to improve this, but they haven't been accepted
upstream (yet).  He has posted also some statistics about the performance
and memory usage impact of symbol resolving to perf list and his blog.

	- Eero

More information about the xubuntu-devel mailing list