On Wed, 2010-12-01 at 15:52 +0800, KOSAKI Motohiro wrote: > > > > > we can't make > > > > > perfect VM heuristics obviously, then we need to compare pros/cons. > > > > if you don't care about small system, let's consider a NORMAL i386 > > > > system with 896m normal zone, and 896M*3 high zone. normal zone will > > > > quickly exhaust by high order high zone allocation, leave a latter > > > > allocation which does need normal zone fail. > > > > > > Not happen. slab don't allocate from highmem and page cache allocation > > > is always using order-0. When happen high order high zone allocation? > > ok, thanks, I missed this. then how about a x86_64 box with 896M DMA32 > > and 896*3M NORMAL? some pci devices can only dma to DMA32 zone. > > First, DMA32 is 4GB. Second, modern high end system don't use 32bit PCI > device. Third, while we are thinking desktop users, 4GB is not small > room. nowadays, typical desktop have only 2GB or 4GB memory. DMA32 isn't 4G, because there is hole under 4G for PCI bars. I don't think 32 bit PCI device is rare too. But anyway, if you insist this isn't a big issue, I'm ok. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom policy in Canada: sign http://dissolvethecrtc.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>