[R] R not giving memory back to system?

[Gardar Johannesson]

This might be because I didn't get it right, but; I thought R would
release memory back to the system as (big) objects get removed?

Here is my platform (with 1Gb of RAM):

platform sparc-sun-solaris2.8
arch     sparc
os       solaris2.8
system   sparc, solaris2.8
status
major    1
minor    3.1
year     2001
month    08
day      31
language R

A little example:

Start a new section of R, with no objects:

> ls()
character(0)
> gc()
         used (Mb) gc trigger (Mb)
Ncells 187633  5.1     407500 10.9
Vcells  36061  0.3     786432  6.0
>

And the top commands shows:

   PID USERNAME THR PRI NICE  SIZE   RES STATE    TIME    CPU COMMAND
 18068 gardar     1  32    0   15M   12M sleep    0:02  0.01% R.bin

Creating few objects:

> x <- numeric(1e7)
> gc()
           used (Mb) gc trigger (Mb)
Ncells   187642  5.1     407500 10.9
Vcells 10036062 76.6   10394092 79.4
> a <- x
> gc()
           used  (Mb) gc trigger  (Mb)
Ncells   187644   5.1     407500  10.9
Vcells 20036061 152.9   20394103 155.6
> b <- x
> gc()
           used  (Mb) gc trigger  (Mb)
Ncells   187646   5.1     407500  10.9
Vcells 30036061 229.2   30394103 231.9
>

And at the end the top command shows:

  PID USERNAME THR PRI NICE  SIZE   RES STATE    TIME    CPU COMMAND
 18068 gardar     1  42    0  244M  241M sleep    0:08  3.47% R.bin

Now, starting removing the objects:

> rm(b)
> gc()
           used  (Mb) gc trigger  (Mb)
Ncells   187646   5.1     407500  10.9
Vcells 20036061 152.9   30394103 231.9
> rm(a)
> gc()
           used (Mb) gc trigger  (Mb)
Ncells   187652  5.1     407500  10.9
Vcells 10036073 76.6   30394103 231.9
> rm(x)
> gc()
         used (Mb) gc trigger  (Mb)
Ncells 187650  5.1     407500  10.9
Vcells  36073  0.3   24315282 185.6
>

But the top command shows:

   PID USERNAME THR PRI NICE  SIZE   RES STATE    TIME    CPU COMMAND
 18068 gardar     1  32    0  244M  241M sleep    0:09  0.17% R.bin

A size of 244Mb (241Mb in memory).

If I run gc() few times...

> gc()
         used (Mb) gc trigger  (Mb)
Ncells 187657  5.1     407500  10.9
Vcells  36086  0.3   19452225 148.5
> gc()
         used (Mb) gc trigger  (Mb)
Ncells 187657  5.1     407500  10.9
Vcells  36086  0.3   15561780 118.8
>

[RUNNING gc() FEW TIMES MORE]

> gc()
         used (Mb) gc trigger (Mb)
Ncells 187657  5.1     407500 10.9
Vcells  36086  0.3     786432  6.0
>


But the top command still shows:

   PID USERNAME THR PRI NICE  SIZE   RES STATE    TIME    CPU COMMAND
 18068 gardar     1  32    0  244M  241M sleep    0:14  0.02% R.bin


My question is; are gc() and unix top telling the same memory story?  If
not, which one is not getting it right?


Cheers,
Gardar

________________________________________________________
Gardar Johannesson
 Department of Statistics
Ohio State University
304E Cockins Hall, 1958 Neil Av.
Columbus, OH 43210
_________________________________________________________


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