On 12:37 Sat 29 Mar , cadetg marco wrote:
> Hi KernelNewbies!
>
> Why are shared libraries hold multiple times in memory even if two
> processes uses the same libraries?
Are they?
> I've made a little test with
> firefox and epiphany both are using the same SO -->
> /usr/lib64/pango/1.6.0/modules/pango-basic-fc.so.
>
> Anyway if I look into /proc/$PID/maps of both processes I can clearly
> see that the library is hold multiple times in ram:
>
> firefox libs --> pango
> 2aaab9e49000-2aaab9e4b000 r-xp 00000000 08:02 7604731
> /usr/lib64/pango/1.6.0/modules/pango-basic-fc.so
> 2aaab9e4b000-2aaaba04a000 ---p 00002000 08:02 7604731
> /usr/lib64/pango/1.6.0/modules/pango-basic-fc.so
> 2aaaba04a000-2aaaba04b000 r--p 00001000 08:02 7604731
> /usr/lib64/pango/1.6.0/modules/pango-basic-fc.so
> 2aaaba04b000-2aaaba04c000 rw-p 00002000 08:02 7604731
> /usr/lib64/pango/1.6.0/modules/pango-basic-fc.so
>
> Epiphany libs --> pango
> 2aaab6287000-2aaab6289000 r-xp 00000000 08:02 7604731
> /usr/lib64/pango/1.6.0/modules/pango-basic-fc.so
> 2aaab6289000-2aaab6488000 ---p 00002000 08:02 7604731
> /usr/lib64/pango/1.6.0/modules/pango-basic-fc.so
> 2aaab6488000-2aaab6489000 r--p 00001000 08:02 7604731
> /usr/lib64/pango/1.6.0/modules/pango-basic-fc.so
> 2aaab6489000-2aaab648a000 rw-p 00002000 08:02 7604731
> /usr/lib64/pango/1.6.0/modules/pango-basic-fc.so
>
> Please see the address differs which results that the library is hold
> multiple times in ram.
These are *virtual* addresses not *physical* addresses. The same virtual
address points to completly different physical memory regions for different
processes. And the same physical address might be accessed with multiple
virtual addresses.
-Michi
--
programing a layer 3+4 network protocol for mesh networks
see http://michaelblizek.homelinux.net
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