On Thu, Mar 01, 2007 at 10:51:00PM -0800, Christoph Lameter wrote: > On Fri, 2 Mar 2007, Nick Piggin wrote: > > > > There was no talk about slightly. 1G page size would actually be quite > > > convenient for some applications. > > > > But it is far from convenient for the kernel. So we have hugepages, so > > we can stay out of the hair of those applications and they can stay out > > of hours. > > Huge pages cannot do I/O so we would get back to the gazillions of pages > to be handled for I/O. I'd love to have I/O support for huge pages. This > would address some of the issues.
Can't direct IO from a hugepage? > > > Writing a terabyte of memory to disk with handling 256 billion page > > > structs? In case of a system with 1 petabyte of memory this may be rather > > > typical and necessary for the application to be able to save its state > > > on disk. > > > > But you will have newer IO controllers, faster CPUs... > > Sure we will. And you believe that the the newer controllers will be able > to magically shrink the the SG lists somehow? We will offload the > coalescing of the page structs into bios in hardware or some such thing? > And the vmscans etc too? As far as pagecache page management goes, is that an issue for you? I don't want to know about how many billions of pages for some operation, just some profiles. > > Is it a problem or isn't it? Waving around the 256 billion number isn't > > impressive because it doesn't really say anything. > > It is the number of items that needs to be handled by the I/O layer and > likely by the SG engine. The number is irrelevant, it is the rate that is important. > > I understand you have controllers (or maybe it is a block layer limit) > > that doesn't work well with 4K pages, but works OK with 16K pages. > > Really? This is the first that I have heard about it. > Maybe that's the issue you're running into. > > This is not something that we would introduce variable sized pagecache > > for, surely. > > I am not sure where you get the idea that this is the sole reason why we > need to be able to handle larger contiguous chunks of memory. I'm not saying that. You brought up this subject of variable sized pagecache. > How about coming up with a response to the issue at hand? How do I write > back 1 Terabyte effectively? Ok this may be an exotic configuration today > but in one year this may be much more common. Memory sizes keep on > increasing and so is the number of page structs to be handled for I/O. At > some point we need a solution here. Considering you're just handwaving about the actual problems, I don't know. I assume you're sitting in front of some workload that has gone wrong, so can't you elaborate? Eventually, increasing x86 page size a bit might be an idea. We could even do it in software if CPU manufacturers don't for us. That doesn't buy us a great deal if you think there is this huge looming problem with struct page management though. - 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/
