2018年6月12日 · mmap works by manipulating your process's page table, a data structure your CPU uses to map address spaces. The CPU will translate "virtual" addresses to "physical" ones , and does so according to the page table set up by your kernel.

2008年11月3日 · One place mmap can be awkward is if you need to work with very large files on a 32 bit machine. This is because mmap has to find a contiguous block of addresses in your process's address space that is large enough to fit the entire range of the file being mapped. This can become a problem if your address space becomes fragmented, where you ...

2017年8月30日 · What's actually happening in most cases is that mmap() is providing copy-on-write access to that file's data in the page cache. As a result, the usual cache restrictions on data lifetime apply: if the system needs space, pages can be dropped (or flushed to disk if they're dirty) from the cache and need to be faulted in again.

2019年1月11日 · mmap method is a little bit more restrictive then shmget, but easier to use. shmget is the old System V shared memory model and has the widest support. mmap/shm_open is the new POSIX way to do shared memory and is easier to use. If your OS permits the use of POSIX shared memory then I would suggest going with that.

2011年1月24日 · Both malloc and mmap are thread-safe. Neither is async-signal-safe per POSIX. In practice, mmap probably works fine from a signal handler, but the whole idea of allocating memory from a signal handler is a very bad idea. If you want to use mmap to allocate anonymous memory, you can use MAP_ANON/MAP_ANONYMOUS.

2016年8月24日 · According to mmap(2) - Linux manual page, offset must be a multiple of the page size as returned by sysconf(_SC_PAGE_SIZE). When the page size is 4096 (a page size used in x86 CPU), 0x000000368d76c0 is not a multiple of 4096 and will be considered as invalid. For that reason, you will have to adjust the offset.

2014年5月23日 · I'm having what appears to be a caching problem when using /dev/mem with mmap on a dual ARM processor system (Xilinx Zynq, to be exact). My configuration is asymmettric, with one processor running Linux and the other processor running a …

2011年6月22日 · mmap() can be optionally supplied with a fixed location to place the map. I would like to mmap a file and then have it available to a few different programs at the same virtual address in each program. I don't care what the address is, …

2013年2月9日 · taken from the malloc man page: Normally, malloc() allocates memory from the heap, and adjusts the size of the heap as required, using sbrk(2). When allocating blocks of memory larger than MMAP_THRESHOLD bytes, the glibc malloc() implementation allocates the memory as a private anonymous mapping using mmap(2).

2018年10月12日 · Kernel has to copy the data to/from those locations. Using mmap() maps the file to process' address space, so the process can address the file directly and no copies are required. There is also no system call overhead when accessing memory mapped file after the initial call if the file is loaded to memory at initial mmap(). If a page of the ...