Sorry Yiqun, I was thinking of virtual memory so you are correct. I also haven't looked into the kernel memory subsystem(s) in a while so I may be a little behind in my knownledge of them. Regards Nick On 2014-11-29 03:54 PM, Yiqun Chen wrote: > Incorrect. The 64 bit machine theoretically supports 2 ^ 64 bytes virtual > memory space but on x86 only 48 out of 64 address buses are used. So we > cannot assume the upper limit of physical space.on different platforms. > And Nick you're confusing with the physical and virtual memory. The usage > of memory for kernel space is not determined by the ratio. It's defined by > mapping strategy. You first need to know why this 3 to 1 was used. It's > because we cannot map all the physical pages onto the corresponding virtual > address since we need to spare some linear space for user program. But on > 64 bits platform we have plenty virtual address for the programmer as the > physical memory is much much smaller than it. On x86_64 we divide > kernel/user space by setting all the first 16 bits with 0 or 1 as the user > or kernel space respectfully. So how large would the kernel space be if we > could use 48-bit linear space? > > On Sat, Nov 29, 2014 at 8:16 PM, nick <xerofoify@xxxxxxxxx> wrote: > >> J.Hwan, >> There is a limit as 64 bit can only support 16 extabytes. Greg is right in >> that there is no real limit >> on modern machines because of this. However from my knowledge, system ram >> is split into a 3 to 1 ratio, >> where 75 percent is for user space and the only quarter is for the >> kernel's memory. So on my system with >> 8 GB of ram, the kernel can use up to 25 percent or 2 GB of ram. >> Hope this answers your question, >> Nick >> On 2014-11-29 12:45 PM, Greg KH wrote: >>> On Sat, Nov 29, 2014 at 12:25:43AM +0900, J.Hwan Kim wrote: >>>> Hi, everyone >>>> >>>> As far as I know, the kernel memory limit is 1GB in 32bit system. >>>> Is it also applicable to 64bit system? >>>> What's the limit of kernel memory in 64bit system? >>> >>> There is no limit :) >>> >>> What do you really want to know this for? >>> >>> greg k-h >>> >>> _______________________________________________ >>> Kernelnewbies mailing list >>> Kernelnewbies@xxxxxxxxxxxxxxxxx >>> http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies >>> >> >> _______________________________________________ >> Kernelnewbies mailing list >> Kernelnewbies@xxxxxxxxxxxxxxxxx >> http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies >> > > > _______________________________________________ Kernelnewbies mailing list Kernelnewbies@xxxxxxxxxxxxxxxxx http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
