>> - doesn't store the accounted value but >> limit - accounted (i.e. the free resource) >> - uses atomic_add_return() >> - when negative, an error is returned and >> the resource amount is added back >> >>changes to the limit have to adjust the 'current' >>value too, but that is again simple and atomic >> >>best, >>Herbert >> >>PS: atomic_add_unless() didn't exist back then >>(at least I think so) but that might be an option >>too ... > > > I think as far as having this discussion if you can remove that race > people will be more willing to talk about what vserver does. > > That said anything that uses locks or atomic operations (finer grained locks) > because of the cache line ping pong is going to have scaling issues on large > boxes.
> So in that sense anything short of per cpu variables sucks at scale. That > said > I would much rather get a simple correct version without the complexity of > per cpu counters, before we optimize the counters that much. fully agree with it. We need to get a working version first. FYI, in OVZ we recently added such optimizations: reserves like in TCP/IP, e.g. for kmemsize, numfile these reserves are done on task-basis for fast charges/uncharges w/o involving lock operations. On task exit reserves are returned back to the beancounter. As it demonstrated atomic counters can be replaced with task-reserves on the next step. Thanks, Kirill - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
