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List:       kde-core-devel
Subject:    Re: Memory overhead of -fexceptions
From:       Waldo Bastian <bastian () kde ! org>
Date:       2001-08-01 15:38:11
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On Wednesday 01 August 2001 02:37 am, Rik Hemsley wrote:
> Subtracting 1 from 2:
>
> VmSize:     2776 kB
> VmLck:         0 kB
> VmRSS:      2100 kB
> VmData:        4 kB
> VmStk:         0 kB
> VmExe:         4 kB
> VmLib:      1460 kB
>
> I don't know if these numbers mean that we actually waste memory.  I can
> see that there is an extra 1.4M of (shared) memory used by the library.

You will have to run 10 or so instances of each to see the actual effects on 
your free memory, since these numbers are a bit crappy (e.g. you don't know 
how much is actually shared between processes).

Anyway, to give an indication, your VmSize increases with 2776 Kb while your 
VmLib (which is supposed to be shared) only increases with 1460 Kb. This 
seems to suggest that you have a 2776-1460 = 1316Kb overhead that isn't 
shared (and, to make my point that memory usage reporting is crappy, this 
1316Kb doesn't show up under any other category)

VmRSS shows that the memory actually used (non-virtual memory) increases with 
2100Kb, unfortunately it is not clear how much of the 1460Kb shared vm is 
responsible for this and how much of 1316Kb non-shared vm is responsible for 
this. It would not surprise me if all of the 1316Kb would end up here. That 
would mean that the overhead of exceptions is 1.3Mb / process due to Qt 
alone. (kdelibs will probably double this then)

This is in line with the numbers that I found quite some time ago, if you 
take the growth (in size) of Qt into account.

Cheers,
Waldo
-- 
Andrei Sakharov, Exiled 1980-1986, USSR, http://www.aip.org/history/sakharov/
Dmitry Sklyarov, Detained 2001-????, USA, http://www.elcomsoft.com/

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