Hi All, I have a query regarding the kernel virtual memory. In this thread some people said the physical address for the kernel virtual address can be obtained by subtracting it from 3G. Physical address = Virtual Address - 3G. Take a simple Case: I have physical memory for eg 128 MB. And I want to access the virtual address 3GB + 256MB. The physical address would be 3GB + 256MB - 3GB which will be 256MB. But the RAM size is just 128 MB. So how will i read the physical memory 256MB because the physical memory i have is just 128MB. Please clarify this to me.. Thanks, Suresh On 9/8/05, Rahul Iyer <idlisambar@xxxxxxxxx> wrote: > srinivas bakki wrote: > > > > > > > > > One feature of page tables is that each page table entry has an > > associated Global 'G' flag set on it. when this is done, those > > entries > > are not flushed even when the CR3 is loaded. I think the kernel can be > > put up using those flags. Also the kernel code is placed in two 4MB > > pages on x86 which supports PSE (Page Size Extensions). This reduces > > TLB misses of kernel code as well as reduces contention for 4K page > > TLB (since 4MB has a separate TLB). > > > > > > > > IIRC on loading the CR3 there has to be a flush on the TLBs. or is it > > that the cachlelines have this G bit to recognise the page not to be > > flushed ? > > Bingo! that's what the G bit is for! :) G stands for Global... meaning > global across all processes (all page tables) > -r > > > > -- > Kernelnewbies: Help each other learn about the Linux kernel. > Archive: http://mail.nl.linux.org/kernelnewbies/ > FAQ: http://kernelnewbies.org/faq/ > > -- Kernelnewbies: Help each other learn about the Linux kernel. Archive: http://mail.nl.linux.org/kernelnewbies/ FAQ: http://kernelnewbies.org/faq/
