Why is mmap faster?

What mmap helps with is that there is no extra user space buffer involved, the “read” takes place there where the OS kernel sees fit and in chunks that can be optimized. This may be an advantage in speed, but first of all this is just an interface that is easier to use.

How do I reserve memory in Linux?

To reserve a memory range from system address space, the reserved-memory node can be used in the device-tree configuration. Each child node defines a specific memory space and can be configured according the different parameters available for the reserved memory nodes as described in the kernel docs.

What is Prot_read?

The prot argument describes the desired memory protection of the mapping (and must not conflict with the open mode of the file). It is either PROT_NONE or the bitwise OR of one or more of the following flags: PROT_EXEC Pages may be executed. PROT_READ Pages may be read. PROT_WRITE Pages may be written.

Is malloc faster than mmap?

Almost always, memory is much faster than disk, and malloc is not what’s costing time. The mmap code is faster because for your program, mmap has resulted in either less disk access, or more efficient disk access, than whatever reads and writes you compared against.

What is reserved memory?

Reserved memory describes storage space that’s set aside by a technology for its use. The idea is that memory reserved for a specific process cannot be used by other processes.

Do you need to call munmap?

munmap happens automatically on exit So if the program is going to exit anyways, you don’t really need to do it. man munmap 4.15 says: The munmap() system call deletes the mappings for the specified address range, and causes further references to addresses within the range to generate invalid memory references.

What is Dev MEM?

/dev/mem is a character device file that is an image of the main memory of the computer. It may be used, for example, to examine (and even patch) the system. Byte addresses in /dev/mem are interpreted as physical memory addresses.

How can I obtain the kernel command line from a module?

How can I obtain the kernel command line from a Linux kernel module? This can be achieved by reading /proc/cmdline, but it seems like there must be an easier way to access the command line from a kernel module than to open and read a file. Show activity on this post.

What is the difference between EFI and kernel command line?

Both sources are combined, but the kernel command line has higher priority. Please note that the EFI variable is only used by systemd tools, and is ignored by the kernel and other user space tools, so it is not a replacement for the kernel command line.

What is the difference between the kernel and systemd?

The kernel, the initial RAM disk (initrd) and basic userspace functionality may be configured at boot via kernel command line arguments. In addition, various systemd tools look at the EFI variable “SystemdOptions” (if available). Both sources are combined, but the kernel command line has higher priority.

What is memmapfile in MATLAB?

Memory-mapping allows you to work with data in a file as if it were a MATLAB array. m = memmapfile (filename,Name,Value) specifies the properties of m using one or more name-value pair arguments. For example, you can specify the format of the data in the file.