On Fri, 2007-07-13 at 17:13 +1000, David Chinner wrote: > On Thu, Jul 12, 2007 at 09:34:57AM -0700, Dave Hansen wrote: > > On Thu, 2007-07-12 at 18:31 +0200, Andrea Arcangeli wrote: > > > On Fri, Jul 13, 2007 at 12:44:49AM +1000, David Chinner wrote: > > > > That's crap. Just because a machine has lots of memory does not > > > > make it OK to waste lots of memory. > > > > > > It's not just wasted, it lowers overhead all over the place. Yes, the > > > benefit of wasting less pagecache may largely outweight the benefit of > > > having a larger page size, but if you've a lot of memory perhaps your > > > working set already fits in the cache, or perhaps you don't fit in the > > > cache regardless of the page size. > > > > Have you guys seen Shaggy's page cache tails? > > > > http://kernel.org/pub/linux/kernel/people/shaggy/OLS-2006/kleikamp.pdf > > > > We've had the same memory waste issue on ppc64 with 64k hardware > > pages. > > Sure. Fundamentally, though, I think it is the wrong approach to > take - it's a workaround for a big negative side effect of > increasing page size. It introduces lots of complexity and > difficult-to-test corner cases; judging by the tail packing problems > reiser3 has had over the years, it has the potential to be a > never-ending source of data corruption bugs.
Yeah, I'm not real happy right now with the complexity of my patches. I had some hope that Christoph's variable page cache cleanups would simplify some of it, but that doesn't really help. I'm working on it though. > I think that fine granularity and aggregation for efficiency of > scale is a better model to use than increasing the base page size. > With PPC, you can handle different page sizes in the hardware (like > MIPS) and the use of 64k base page size is an obvious workaround to > the problem of not being able to use multiple page sizes within the > OS. > > Adding a workaround (tail packing) to address the negative side > effects of another workaround (64k base page size) ignores the basic > problem that has led to both these things being done: Linux does not > support multiple page sizes natively..... I'd much prefer having support for multiple page sizes. I have to admit that I don't know the VM well enough to weigh in on that debate. Thanks, Shaggy -- David Kleikamp IBM Linux Technology Center - 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/