What is Highmem and Lowmem?
The virtual address space of the kernel (1 GB sized in a 3G/1G split) is divided into two parts: Low memory or LOWMEM, which is the first 896 MB. High memory or HIGHMEM, represented by the top 128 MB.
Why is high memory zone not needed in 64 bit machine?
The kernel space is the “high” 1GB hence the name “high memory problem”. A 64-bit system can address a huge amount of memory – 16 EB -so this issue does not occur there. With 32-bit addresses, you can only address 2^32 bytes of memory (4GB).
What is kernel memory space?
Kernel Space is a memory that constitutes the central core of a computer operating system. It is in-fact a process, that controls all other processes, and it has complete control over everything that occurs on the system.
What are the 3 types of computer memory?
There are three main types of memory: working memory, short-term memory, and long-term memory. Working memory and short-term memory allow you to store and use temporary information, while long-term holds your lifelong memories.
What’s the difference between highmem and kernel space?
HIGHMEM is a range of kernel’s memory space, but it is NOT memory you access but it’s a place where you put what you want to access. A typical 32bit Linux virtual memory map is like: 0x00000000-0xbfffffff: user process (3GB) 0xc0000000-0xffffffff: kernel space (1GB)
Which is the highmem mapping in Linux 2.6?
This is the highmem mapping type used most in the 2.6 kernel. On a system with 2GB memory, a little more than half of the memory will be in high memory (ZONE_HIGHMEM) and a little less than half of memory will be in so-called low memory (ZONE_NORMAL and ZONE_DMA).
How does the Linux kernel split up the memory?
The linux kernel splits that up 3/1 (could also be 2/2, or 1/3 1) into user space (high memory) and kernel space (low memory) respectively. Every newly spawned user process gets an address (range) inside this area.
How much address space does the Linux kernel have?
In this architecture, traditionally the Linux kernel has split the 4GB of virtual memory address space into 3GB for user programs and 1GB for the kernel. On traditionally sized (for lack of a better euphemism) 32 bit systems, this meant the kernel could map all of physical memory into its address space, which makes it possible to: