Hello, On Mon, Apr 26, 2010 at 10:17:49AM +0100, Enrico Zini wrote: > My laptop has 2GB of RAM, but sometimes I want to sync directory trees > with a similar order of magnitude of data in them. When unison scans the > local data, linux has a tendency to swap out running application to free > RAM for caching the data that unison reads. The result is that while > unison is running, my laptop is thrashing heavily as the kernel loads > back from swap those apps that it just swapped. > > I'm running with default kernel VM settings. Running unison under > nocache (http://www.enricozini.org/2010/tips/nocache/) does not cause > the thrashing and keeps the system perfectly usable during syncs, if a > bit slower I/O wise, which is perfectly reasonable. > > I am of course the first to agree that the problem in this is not in > unison but in Linux itself. The operating system should not swap out > running apps: this behaviour is preposterous, and everytime I experience > it a part of my soul dies drowned by its own tears. > > It might still make sense, however, to have an option in unison > (disabled by default) that turns on fadvise cache hinting. One would > turn it on when syncing big, seldom accessed archives like photo > galleries or music collections, and keep it off when syncing the home > dir with files that are accessed often. > > Even more ideal would be to be able to turn it on/off on a per-directory > basis, so that I can sync my home dir and have the system cache > everything except pictures, music and videos. >
I played a bit with fadvise and I even have an OCaml binding for it, somewhere on my hard-drive. I think it can be quite efficient but you should talk about this directly with upstream. I forward this mail to upstream, so that you can discuss it. The original bug is here: http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=579213 Regards Sylvain Le Gall -- To UNSUBSCRIBE, email to [email protected] with a subject of "unsubscribe". Trouble? Contact [email protected]
