Depends on what exactly you want to use it for. If you want to map existing files into memory, that’s supported with memory-mapped files. They can also be used to share memory between processes (use named mapping object with no underlying file). If you want to map physical memory, that’s generally not supported from user … Read more
Anonymous mappings can be pictured as a zeroized virtual file. Anonymous mappings are simply large, zero-filled blocks of memory ready for use. These mappings reside outside of the heap, thus do not contribute to data segment fragmentation. MAP_ANONYMOUS + MAP_PRIVATE: every call creates a distinct mapping children inherit parent’s mappings childrens’ writes on the inherited … Read more
Reads back to what? What is the final destination of this data? Since it sounds like you are completely IO bound, mmap and read should make no difference. The interesting part is in how you get the data to your receiver. Assuming you’re putting this data to a pipe, I recommend you just dump the … Read more
I heard (read it on the internet somewhere) that mmap() is faster than sequential IO. Is this correct? If yes then why it is faster? It can be – there are pros and cons, listed below. When you really have reason to care, always benchmark both. Quite apart from the actual IO efficiency, there are … Read more
From IEEE 1003.1: The mmap() function shall establish a mapping between a process’ address space and a file, shared memory object, or [TYM] typed memory object. It needs all the virtual address space because that’s exactly what mmap() does. The fact that it isn’t really running out of memory doesn’t matter – you can’t map … Read more
Look folks, contrary to common believe, mmap is indeed a memory allocation function similar to malloc.. the mmaped file is one use of it.. you can use it as memory allocation function passing -1 as file descriptor.. so.. the common use is to use malloc for tiny objects and mmap for large ones.. this is … Read more
The following analysis applies only to glibc (based on the ptmalloc2 algorithm). There are certain options that seem helpful to return the freed memory back to the system: mallopt() (defined in malloc.h) does provide an option to set the trim threshold value using one of the parameter option M_TRIM_THRESHOLD, this indicates the minimum amount of … Read more
MAP_PRIVATE mappings require a memory reservation, as writing to these pages may result in copy-on-write allocations. This means that you can’t map something too much larger than your physical ram + swap. Try using a MAP_SHARED mapping instead. This means that writes to the mapping will be reflected on disk – as such, the kernel … Read more
Both methods are viable. 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 … Read more