Re: Why the page tables are needed for lowmem?
On 06/18/2014 11:21 PM, sandeep kumar wrote: Hi All i was going through mm initialization code, and saw paging_init() implementation. it has a function map_lowmem(). I was wondering why do we need page table entries for lowmem ?? because all the pages in lowmem can be addressed by kernel logical address and differ only an offset from the physical address. Why cant we simply add that offset to the virtual(logical) address and get the job done. Why waste some memory for creating PTEs for them? can any one clarify? Because after switching the CPU to protected mode, the CPU can only access memory through page tables, and can no longer do loads, stores, etc to physical memory addresses. ___ Kernelnewbies mailing list Kernelnewbies@kernelnewbies.org http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
Re: Why the page tables are needed for lowmem?
On Thu, Jun 19, 2014 at 8:51 AM, sandeep kumar coolsandyfor...@gmail.com wrote: Hi All i was going through mm initialization code, and saw paging_init() implementation. it has a function map_lowmem(). I was wondering why do we need page table entries for lowmem ?? I hope you understand how MMU and virtual memory works. because all the pages in lowmem can be addressed by kernel logical address and differ only an offset from the physical address. Why cant we simply add that offset to the virtual(logical) address and get the job done. Why waste some memory for creating PTEs for them? Let's forget about lowmem or high mem. See the role of MMU and you'll understand why it's needed. can any one clarify? -- With regards, Sandeep Kumar Anantapalli, ___ Kernelnewbies mailing list Kernelnewbies@kernelnewbies.org http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies -- ---P.K.S ___ Kernelnewbies mailing list Kernelnewbies@kernelnewbies.org http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
