I'm using rsync on my fileserver to backup the data. The problem is that rsync doesn't seem to release the memory it uses. After booting ~20 MB of memory is in use. This jumps up to 270 MB after running rsync. I know rsync uses quite a bit of memory when it's running, but surely it should be released upon completion.

Here's the situation after booting the system (free -m):
... and here after running rsync:
Very troublesome, any ideas?

Linux uses all the RAM it can find for active progs and caches. If a program exits, the RAM remains cached until another process needs it, at which pt the kernel will flush the old/unwanted stuff and re-use the RAM for the new proc.
The kernel handles all this transparently.
IOW, ignore it, it's not an issue.

I knew someone would say that That's why I posted the output of the free command in the first place.

I know about Linux caching. However, if you take a look at the output of the free command above, you'll notice that 480 MB of total memory is in use and only 156 MB cached + 53 MB buffered (i.e. 209 MB), so I'm still missing the mentioned 270 MB (well, 271 MB actually, but that's a rounding error). It _is_ an issue because after a couple of rsyncs almost all the memory is used (disappeared, not cached+buffered) and the system becomes very unresponsive.

Anyone?

Wow . . . well, if you really think that rsync is leaking or failing to free memory, then I would suggest building a fresh version from source or downloading another binary and seeing if it still happens. I know that rsync does not do this to me.

If it still happens, the problem may not be with rsync.

Are we talking Slackware 13 here?

Nope, it's not Slack 13, it's 11 (with all the available upgrades installed, though). So far I've seen no reason to upgrade it since 11 really does everything I want it to do. rsync is version 2.6.9 on this system. I'll try to build a newer one to see if that works better.

I've seen the same think after rsyncing a largish directory tree. From the bit of research I did, it seems to be attributable to dentries /inode buffers. You can flush those buffers and reclaim the memory by doing:

But I don't think it's really necessary. Linux will eventually reclaim the memory when needed.

A note about rsync: it's recommended to have the same rsync version on both ends of the transfer for best performance and to avoid possible issues. And v. 3 brings some important changes -- have a look through the release notes.

drop_caches doesn't work with 2.4 series kernel. I think I'll just compile a newer version of rsync and see how that goes.

I'm running RHEL5.4 and am using rsync for backup onto a 2nd disk (something like poor man's RAID 1). This worked for me. Thanks!