-----Original Message----- From: Naidu, Venkata [mailto:Venkata.Naidu@xxxxxxxxxxx] Sent: Tuesday, October 12, 2004 3:26 AM To: jonathan@xxxxxxxxxxxxxx Cc: kernelnewbies Subject: RE: memory used by kernel? > 1. why do we need page tables for kernel memory from PAGE_OFFSET > to HIGHMEM, if the conversion is direct. Isn't it just sufficient > to maintain kernel page tables for HIGHMEM, instead of NORMAL. The CPU uses the MMU to translate virtual address to physical address irrespective of whether it is running in kernel mode or user mode and hence u need page tables for kernel too. More over, normally, kernel virtual address 0xc000 0000 (PAGE_OFFSET) corresponds to physical address 0x0 (or some other physical address, depends on the board) and so on. It is through the page table entries that this is made possible. > 2. Let us consider there is some advantage of maintaining kernel > page table (along with every process page table), then, kernel > page table also mush reside in memory always (even if the linux > kernel is not pageable). If the kernel page table is in memory > always, isn't it trivial to implement kernel memory as pageable. > What is the rational behind the kernel being not pageable? AFAIK, by making kernel non pageable the kernel development is made much eazy. > 3. Does each and every kernel address mapped in every process > virtual memory (some where in between 3GB to 4GB). Even > when kernel does a kmalloc from interrupt context? For any process, the PTEs that corresponds to kernel mode addresses will be the same. The ISR runs at the context of the currently scheduled process. -- Kernelnewbies: Help each other learn about the Linux kernel. Archive: http://mail.nl.linux.org/kernelnewbies/ FAQ: http://kernelnewbies.org/faq/
