On 2007-02-12 20:30, Dan Streetman wrote: > On 2/11/07, Kevin Brosius <[EMAIL PROTECTED]> wrote: > > On 2007-02-05 20:24, Dan Streetman wrote: > > > On 2/5/07, Nicolas Maufrais <[EMAIL PROTECTED]> wrote: > > > > Heroine Virtual Ltd recommends disabling swap when a lot of memory is > > > > installed. > > > > > > This is not a good idea under any circumstances. Disabling swap will > > > never help anything or improve performance, ever. It will only cause > > > the system to start killing processes when you use up all system > > > memory. Do not disable swap. > > > > Hi Dan, > > > > This will only be true for kernels with the OOM killer running, right? > > Is "running" the right adjective? I think the OOM killer is part of > the memory allocation subsystem, not a kernel process, right? So ever > since it was added to the kernel it is there. I don't think you can > build a kernel without it these days, can you? But if you mean > kernels before the OOM killer was added, sure...that was a looong time > ago tho.
Well, I thought it could be disabled. There's been discussion of that on lkml a few times. But I'm not up to date. > > But that's beside the point. If you run out of memory, either the > kernel kills picks a single program to kill and let everything else in > the system live (i.e. with OOM killer), or _everything_ on the system > dies a slow and painful death (i.e. without OOM killer). > > > Here's the link to comments from Cinelerra's author about swap usage: > > http://cvs.cinelerra.org/docs/wiki/doku.php?id=english_manual:cinelerra_cv_en_20 > > I've seen system behavior that makes me believe his comments about disk > > caching using system memory (back in ext2 days.) Maybe this is no > > longer true for newer kernels. But I suspect your 'never help' comment > > might be overzealous. ;) Would you say newer kernels with current > > versions of filesystems no longer exhibit this behavior? Or is > > something else going on here? > > Ok, maybe "never help" is a bit extreme... ;-) > > Recent kernels do not start swapping pages out when memory is 1/2 full > (as stated in that FAQ). I'm typing this from a system with 1G of > memory, 900M of which is in use right now, and swap is 588K. I've > been using Linux (Slackware) since 1997, and I don't ever remember > that behavior. But hey, I can't say for sure that it has never been > true. There very well may be some very old kernels that swap > overzealously like that...I can only say I've never seen it in ~10 > years of Linux use. 1997... yeah, about the same here. ext2 used to heavily cache files. The only reason I know this is because I used to be able to build an xfree86 source tree, and a second compile could sometimes run without disk access. That tree was on the order of 100M at the time. I could imagine that disk cache might have been weighted poorly in the paging algorithm at some point. If that was half the mem, then the swap comments above might be related to that. Remember, we are talking about Cin usage, which would be disk intensive for render writes/reads, along with page hungry for effects processing. The mix may be different for single app usage than the test case you suggest below. The disk caching is interesting, because with the advent of reiser, and slightly newer kernels, I noticed that disk caching was nothing like ext2. It would not cache an entire 100M source code true when accessed with reiser, although that may have been an artifact of slightly newer kernels. I do not recall if I tested that or not. > I would recommend 2 things, first get a program that constantly > monitors system stats (I run xosview 100% of the time and have for > many years...xosview.sf.net). Then second, (with swap enabled) start > up cinelerra and/or some other large programs and start eating up > memory. See at what point swapping starts and how much memory is > swapped. See what happens when program memory requirements exceed > system memory, i.e. used system memory + swap used exceed total system > memory. Then shut everything down and disable swap, and start up > those programs again and eat up more than system memory and see what > happens (hint: don't be doing anything important when you try this > :-). Until system memory ran out, was the no-swap case any better > than the swap case? Was swap significantly used before system memory > usage run up to near 100%? What happened when you ran out of memory > and had no swap? > So, you think disk caching has no impact? Possible, I haven't tried testing on a 4G machine. > I suspect everyone will find that the system behaves identically until > memory usage gets very close to total available system memory, and > when memory usage exceeds available system memory the swap/no-swap > cases are very different. But if the test shows no-swap is better for > you, by all means don't use swap... -- Kevin _______________________________________________ Cinelerra mailing list Cinelerra@skolelinux.no https://init.linpro.no/mailman/skolelinux.no/listinfo/cinelerra
