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Re: Prelink hates me



On Sat, 2004-04-10 at 15:11, Simon Perreault wrote:
> Scott Sloan wrote:
> 
> > Prelink ran not 5 mins ago and I notice a huge increase in memory usage,
> > jumping from 15% to 94%, nothing changing but prelink running. I was
> > wondering if anyone else has had a similar occurrence?
> 
> I witnessed the same behavior, and it is 100% reproducible. The memory 
> seems to not be owned by any process (using top and ps). It is really 
> used because the system starts to swap when I try to start a new 
> program. And this happens with 768 MB of RAM. Is it normal, or is 
> prelink to blame?

ok so there are 2 rational sides to this that aren't a bug:
1) prelink will read in a lot of files into the filesystem cache, since
it'll have to know detailed information about a lot of libraries to do
it's job, only way to get that is to read them in.

2) normally, when 5 running binaries use the same library, there is only
one copy of that library in memory. However, when a library gets
prelinked, a *new copy* of that library is put on disk (one with all the
prelink information), and new binaries that start and use that library
won't and cannot share it with the existing running binaries, so this
leads to temporarily increased real memory usage (temporary because
eventually all apps that use keep the old libs "in use" exit and only
"new library" applications are running). The exception can be very long
running applications (like cron.weekly) which now have library stuff
that is hardly ever used and the VM subsystem may choose to swap some of
that out.


Now I'm not saying that what you see is exclusively one of these, nor am
I saying there's no bug, but at least the cache subsystem showing lots
of ram is expected (and it should be given up mostly when it's needed).

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