On 04Nov2009 09:56, Alan Cox <alan@xxxxxxxxxxxxxxxxxxx> wrote: | On Wed, 4 Nov 2009 14:22:22 +1100 | Cameron Simpson <cs@xxxxxxxxxx> wrote: | > On 04Nov2009 14:01, I wrote: | > | On 03Nov2009 23:45, Alan Cox <alan@xxxxxxxxxxxxxxxxxxx> wrote: | > | | Such as the kernel ... which is much happier in 64bit mode with over 1GB | > | | of RAM. [...] | > | I'm not doubting you, but I would like to have a mental model of roughly | > | why and how 64-bit mode benefits a system. [...] | If you have more than 1GB of memory then the kernel in 32bit mode has to | do extra work because it needs to maintain access to both virtual | mappings and physical mappings | | Normally 32bit memory is laid out as | | [0-3GB] User application address mapping (as the user space sees it) | [3G-3.xG] Mapping of almost 1GB RAM of physical ram | [3.xG-4G] Vmalloc/io mappings/etc | | which takes all the 4GB. To support > 1GB of RAM the kernel has to create | and destroy mmu mappings and access them indirectly which has a big cost. | | In 64bit mode there is plenty of space for all the application and | mappings of main memory so that isn't required. Thank you! Cheers, -- Cameron Simpson <cs@xxxxxxxxxx> DoD#743 http://www.cskk.ezoshosting.com/cs/ Like dogs and muggers, transistors can sense fear. - Norman Yarvin -- fedora-list mailing list fedora-list@xxxxxxxxxx To unsubscribe: https://www.redhat.com/mailman/listinfo/fedora-list Guidelines: http://fedoraproject.org/wiki/Communicate/MailingListGuidelines
