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Does kernel allocate memory?
The kernel usually wants physically contiguous memory. Often, the kernel must allocate the memory without sleeping. Mistakes in the kernel have a much higher price than they do elsewhere.
What is the maximum memory that can be allocated using Vmalloc?
The vmalloc upper limit is, in theory, the amount of physical RAM on the system. VMALLOC_START to VMALLOC_END. Practically speaking, on the IA-32, the range is small; usually just 120 MB. This is an enormous virtual range: 32 TB !
What is memory map in Linux?
Memory mapping is one of the most interesting features of a Unix system. From a driver’s point of view, the memory-mapping facility allows direct memory access to a user space device. If that is the case, the user space process can then use the mmap() system call on a file descriptor associated with the device.
Does Kmalloc return physical address?
1 Answer. You’re right, kmalloc is returning a virtual address, not a physical one. The memory map you linked to is describing the virtual memory map, not the physical memory map. A virtual address typically is translated to a physical address by the MMU when you access data at the address.
How big is the memory in the Linux kernel?
Complete virtual memory map with 5-level page tables ¶ With 56-bit addresses, user-space memory gets expanded by a factor of 512x, from 0.125 PB to 64 PB. All kernel mappings shift down to the -64 PB starting offset and many of the regions expand to support the much larger physical memory supported.
How is the address space mapped in the Linux kernel?
In the Linux kernel it is possible to map a kernel address space to a user address space. This eliminates the overhead of copying user space information into the kernel space and vice versa. This can be done through a device driver and the user space device interface (/dev).
Is there a memory limit for 64 bit Linux?
On 64-bit linux, the maximum memory space for a single process is 2^48 bytes. (In theory, more is possible, but current chips do not allow the entire virtual address space of 2^64 bytes to be used.)
How much address space can a 32 bit process use?
With the 64-bit x86_64 kernel, a 32-bit process can use the entire 4GB address space, except for a couple pages (8KB) at the end of the 4GB address space which are managed by the kernel. The kernel itself uses a part of the address space that is beyond the 4GB accessible to 32-bit code, so it does not reduce the user address space.