Hi! On 17:57 Thu 21 Jun , Vijay Chauhan wrote: > Hello, > > I am newbie. > It has been said "kernel memory is not pageable" > What does it mean? There is no concept of kernel virtual address? > > Any simple explanation will help me to udnerstand. The right term is actually "kernel memory is not swappable". Swapping means writing inactive memory to disk and then using it for something else. Kernel memory not being swappable is a design decicion made in the early linux days. Operating systems which swap kernel memory need to isolate everything which should not be swappd out (e.g. things needed for swap-in, realtime stuff, security sensitive data, ...). This is quite a bit of work. I also guess it is pretty pointless nowadays. Installed memory and is getting so huge that virtual memory developers have a hard time trying to keep cpu-usage overhead for swapping user space memory low. > There is no concept of kernel virtual address? Kernel memory uses virtual addresses as well. However, these the entire system memory is continuously mapped somewhere in the virtual address space. The drawback is that fragmentation turns allocation of large continuous memory regions into a game of luck. There is also an virtual address area (vmalloc) which is used to dynamically map multiple scattered pages to a continuous region. But this is rather slow and rarely used. You might want to take a look at: http://lwn.net/Kernel/LDD3/ -Michi -- programing a layer 3+4 network protocol for mesh networks see http://michaelblizek.twilightparadox.com _______________________________________________ Kernelnewbies mailing list Kernelnewbies@xxxxxxxxxxxxxxxxx http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
