On Thu, 2008-07-24 at 14:40 -0700, Nifty Fedora Mitch wrote: > On Thu, Jul 24, 2008 at 01:49:34PM +0100, Howard Wilkinson wrote: > > > > I am looking for a definitive answer to the question of where the PAE > > kernels become useful. I have seen various articles that mention needing > > PAE kernels if you have more then 4GB of physical memory in a 32-bit > > processor environment. I have also seen statements that say you need > > them if you have 4GB or more of memory. Now which is right? Also, even > > if you need a PAE kernel because the last few bytes are not addressable > > when you have exactly 4GB is this useful or is the trade off of larger > > page tables and pages going to eat any benefit of being able to address > > these few bytes and if so when does the PAE kernel become useful? > > > > http://en.wikipedia.org/wiki/Physical_Address_Extension > > Can you be more specific and define 'useful'. > > In general on a 32 bit system you will have 32 bit pointers by default... > signed arithmetic gives you an effective 2GB process size. Compare and > contrast lseek() and lseek64()... sizeof(off_t something). 32 bits gives you a 4GB address space. Pointers are not signed (and the off_t type reflects this, which is why it's different from int). > But if you have six 2GB processes running on a 6.x GB system is that useful? > Are you playing with one Big process. > > Do you have a test case or pointer to a test case (best) so folks with > large memory systems can sanity test this for you? I suspect the question is related to accessing *physical* (not virtual) memory. poc -- fedora-list mailing list fedora-list@xxxxxxxxxx To unsubscribe: https://www.redhat.com/mailman/listinfo/fedora-list
