On Fri, Jun 01, 2012 at 11:19:40PM +0200, Carlos Alberto Lopez Perez wrote: > On 01/06/12 13:33, Goswin von Brederlow wrote: > >> > I don't know the ultimate reason behind this ugly behaviour of Linux > >> > when the swapping process is happening, but I know this is real and it > >> > happens because I have experimented this situation myself more than a > >> > couple of times. > > It's a matter of that gets swapped and linux choosing the wrong thing to > > swap (far too often). There is some "bug" in linux that when you have > > lots and lots of IO at some point the swap heuristics tip over and start > > swapping apps and usefull data to create more cache space for > > IO. Doesn't matter that you already have 3GB for cache, it still swaps > > out your mouse cursor and then things go real bad. > > This makes sense. Many times I have experimented this situation while > copying a large file from a quick device (hdd) to a very slow device > (cheap usb stick) > > IMHO The logical way of behaving in such situation is to slow-down the > IO bandwidth of the processes that are filling the cache, by sending to > sleep any process that requests more IO while the cache is full instead > of trying to free RAM by swapping out things from the RAM to the swap. > > Do you know any way to avoid (or mitigate) this? Perhaps some sysctl > variable? > > Can't Linux be configured to just block (sleep) any process that > requests IO while the cache is full? > > Perhaps a good idea would be to limit the cache size on a per-PID basis > and block (sleep) the pid while its cache is full.
I don't think it makes any sense to have a hard per-process limit. Also, it's not generally possible to account dirty pages to specific processes exactly. But I think you will be pleased with this change that was included in Linux 3.2: http://lwn.net/Articles/456904/ Ben. -- Ben Hutchings We get into the habit of living before acquiring the habit of thinking. - Albert Camus -- To UNSUBSCRIBE, email to debian-devel-requ...@lists.debian.org with a subject of "unsubscribe". Trouble? Contact listmas...@lists.debian.org Archive: http://lists.debian.org/20120602000140.ge20...@decadent.org.uk
