[R] save/load doubles memory

[Ross Boylan]

Saving and loading data is roughly doubling memory use.  I'm trying to
understand and correct the problem.

R1 was an R process using just over 2G of memory.
I did save(r3b, r4, sflist, file="r4.rdata")
and then, in a new process R2,
load(file="r4.rdata")

R2 used just under 4G of memory, i.e., almost double the original
process.  The r4.rdata file was just under 2G, which seemed like very
little compression.

r4 was created by
r4 <- sflist2stanfit(sflist)

I presume that r4 and sflist shared most of their memory.
The save() apparently lost the information that the memory was shared,
doubling memory use.

R 2.15.1, 64 bit on linux.

First, does my diagnosis sound right?  The reports of memory use in R2
are quite a bit lower than the process footprint; is that normal?
> gc()  # after loading data
            used   (Mb) gc trigger   (Mb)  max used   (Mb)
Ncells   1988691  106.3    3094291  165.3   2432643  130.0
Vcells 266976864 2036.9  282174979 2152.9 268661172 2049.8
> rm("r4")
> gc()
            used   (Mb) gc trigger   (Mb)  max used   (Mb)
Ncells   1949626  104.2    3094291  165.3   2432643  130.0
Vcells 190689777 1454.9  282174979 2152.9 268661172 2049.8
> r4 <- sflist2stanfit(sflist)
> gc()
            used   (Mb) gc trigger   (Mb)  max used   (Mb)
Ncells   1970497  105.3    3094291  165.3   2432643  130.0
Vcells 228827252 1745.9  296363727 2261.1 268661172 2049.8
> 

Even weirder, R1 reports memory use well beyond the memory I show the
process using (2.2G)
> gc()
             used   (Mb) gc trigger   (Mb)  max used   (Mb)
 Ncells   3640941  194.5    5543382  296.1   5543382  296.1
 Vcells 418720281 3194.6  553125025 4220.1 526708090 4018.5


Second, what can I do to avoid the problem?

I guess in this case I could not save r4 and recreate it, but is there a
more general solution?

If I did myboth <- list(r4, sflist) and
save(myboth, file="myfile")
would that be enough to keep the objects together?  Judging from the
size of the file, it seems not.

Even if the myboth trick worked it seems like a kludge.

Ross Boylan