On 08/19/2010 02:15 PM, Michael Hennebry wrote: > On Thu, 19 Aug 2010, JD wrote: > >> Problem comes as Michael explains, that when a process needs a large >> "physically contiguous" chunk of memory, it might not be available. >> That said, usually, requests for physically contiguous memory is only >> needed when wanting to map very large number of DMA pages for >> doing direct physical I/O. >> Otherwise, a process itself does not need to have physically contiguous >> pages. Only the virtual space allocated to that "malloc" or large buffer >> declaration in a program, is contiguous. > Why would malloc or a large buffer declaration > require physically contiguous memory? It is done in a driver on the process' behalf when doing direct physical IO . typically, such blocks of physically contiguous chunks memory are set aside during boot. I have also seen special embedded linux drivers that provide an ioctl to let the process get a set of physically contiguous pages and map the space to user virtual space. This is for performance reasons to reduce copying from user space to kernel space when large amounts of data need to be moved. This is not a new idea. it has been around for many years. I first saw it in Linux back in 1998/1999. -- users mailing list users@xxxxxxxxxxxxxxxxxxxxxxx To unsubscribe or change subscription options: https://admin.fedoraproject.org/mailman/listinfo/users Guidelines: http://fedoraproject.org/wiki/Mailing_list_guidelines
