R on Mac building up memory usage

Hi,

I guess this may be not a specificity of r-sig-geo but as I am using
library(rgdal)
library(rgeos)

in this script so it may be the reason? (perhaps I should try running
something else to check).

So basically I am running some code reading  61288 features and other
things ... if I run it once I got in gc():

gc()

          used (Mb) gc trigger  (Mb) max used  (Mb)
Ncells 1833926 98.0    5103933 272.6  9968622 532.4
Vcells 2437534 18.6    7056348  53.9 11036325  84.3

and on the monitor it says R is using 3.3Go.

Then I remove everything rm(list=ls()) and run it again trying different
sets of parameters for example.
Second run similar gc() but R is using 6.4Go

gc()

          used (Mb) gc trigger  (Mb) max used  (Mb)
Ncells 1834325 98.0    6323353 337.8  9968622 532.4
Vcells 2439267 18.7    7572947  57.8 11832730  90.3


After a while and few other computation I get R is using 10Go
and gc() gives

gc()

          used (Mb) gc trigger  (Mb)  max used  (Mb)
Ncells 1863272 99.6    5944937 317.5   9968622 532.4
Vcells 2503503 19.2    8462995  64.6 100858653 769.5
rm(list=ls())

ls()

character(0)

gc()

         used (Mb) gc trigger  (Mb)  max used  (Mb)
Ncells 608451 32.5    4755949 254.0   9968622 532.4
Vcells 760517  5.9    6770396  51.7 100858653 769.5

but  still 10Go for R in the monitor.
I had experienced a building up to 50Go then my system tells me to close
some apps, all that doing the same running one set, then rm(list=ls())
... So at the moment I just have to close and re-start R?

Didier