Re: [9fans] automatic page sharing

[Ethan Grammatikidis <eekee57@fastmail.fm>]

On Thu, 29 Oct 2009 21:25:59 +0100
Enrico Weigelt <weigelt@metux.de> wrote:

> Russ Cox wrote:
>
> Hi,
>
> >> Assuming statically linked-in libraries are properly aligned,
> >> we'll have lots of equal pages in the system, so the kernel could
> >> find and automatically map them together.
> >
> > This is not true.  When static libraries are linked into
> > a target binary, only the necessary objects are taken,
> > and all the symbol references are resolved (avoiding
> > the need for relocation at load time), and the code is
> > not position-independent.  So even if they were "properly
> > aligned", the bits of common code would be very small.
>
> Assuming PIC, of course ;-)
>
> My idea is to get rid of mmap() for shared libraries but w/o
> loosing the code sharing behind the scenes.

Pardon if this has come up before, but what about the greatly
increased time taken to launch a shared-lib program?  That's quite
unsuitable for the typical unix commands intended to be used
repeatedly, and produces unacceptable load times for apps depending on
many libraries.  I remember Gnome and KDE just before pre-linking was
introduced, they weren't fun.  Are you planning to incorporate
pre-linking or something like it to offset this disadvantage?

Shared libs are like object-oriented programming languages: they allow
you to introduce much greater complexity to a single program but bring
disadvantages too.  There are other ways to deal with the problem such
as (on Plan 9) breaking up the program into servers or commands +
front end, a solution which may also greatly increase the flexibility
of the application.


--
Ethan Grammatikidis

Those who are slower at parsing information must
necessarily be faster at problem-solving.