On Tue, 24 Jun 2003, [iso-8859-1] pankaj chauhan wrote: > > > hi all , > > i have following doubts regarding memory mgt : > > 1 .what is the difference between - Kernel logical address and kernel virtual address . I dont think there is any difference between these two. Please correct me if I am wrong. > > 2. how the boundry between low memory and high memory is set. i mean how the ammount of high or low memory of a system is decided . > In linux kernel's virtual address space extends form 3GB to 4GB. So whole of the physical RAM is mapped to the kernel address space is mapped from 3GB. So if the physical RAM is greater than 1GB then there arises a problem as the kernel cannot address this physical space. So to support and use the physical memory that is greater than 1GB high memory concept is used. The memory from this part is mapped temporarily into the low memory using kmap() and kunmap() so that the kernel can use all the memory. a memory node is split into different zones. In UMA there is only one node and the zones are DMA, NORMAL and HIGHMEM. DMA is 16MB and NORMAL which is the low memory ranges from 16MB to 896MB and HIGHMEM starts from 1GB. if the physical memory is less than 1GB then there is no high memory. HTH, raghu > thanks , > > Regards, > > pankaj chauhan > > > > > > SMS using the Yahoo! Messenger;Download latest version. -- Kernelnewbies: Help each other learn about the Linux kernel. Archive: http://mail.nl.linux.org/kernelnewbies/ FAQ: http://kernelnewbies.org/faq/
