On Fri, July 27, 2007 22:34, Arjan van de Ven wrote: > On Fri, July 27, 2007 21:43, Al Boldi wrote: >> IMHO, what everybody agrees on, is that swap-prefetch has a positive effect >> in some cases, and nobody can prove an adverse effect (excluding power >> consumption). The reason for this positive effect is also crystal clear: >> It prefetches from swap on idle into free memory, ie: it doesn't force > > the fact that there is free memory is ... strange. IN principle, Linux > keeps almost no memory free (except some emergency buffers) so that > things you swap in prematurely will BY DEFINITION go at the expense of > other things that could be there....
It's not strange, the use case here is if something memory hungry process is shut down it leaves behind a lot of free memory. Having things swapped out while there's free memory is strange, so swap prefetch fills it up again. > also, they take up seek time (5 to 10 msec), so if you were to read > something else at the time you get additional latency. If there's other disk activity swap prefetch shouldn't do much, so this isn't really true. >> Conclusion: Either prove swap-prefetch is broken, or get this merged quick. There are a whole lot of other requirements too than that it isn't broken (of which most are fulfilled, but anyway). One reason could be that there's a better solution out there for the problem swap prefetch tries to solve. That said, as swap prefetch is here now for a while and that other solution not it's not such a great argument. Personally I think that a more generic solution would be better, one that prefetches the lastly evicted pages back in, not favouring either of swap or file data, like swap prefetch does now. Greetings, Indan - 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/