问题
I have a program that maps quite a few (100's) of sizable files 10-100MB each. I need them all mapped at the same time.
At the moment I am calling open followed by mmap at the beginning of the program, followed by munmap and close at the end.
Often I have to adjust the open files limit running ulimit -n before running the program.
Question is do I actually need to keep the files open, or can I open mmap close do some large data processing then munmap when I'm finished.
The man pages of mmap do not seem terribly clear to me on this one.
回答1:
No, at least not on Linux it's fine to close the file.
The manual page clearly states:
On the other hand, closing the file descriptor does not unmap the region.
For portability, I also checked the POSIX manual, it says the same thing (although even more clearly):
The mmap() function adds an extra reference to the file associated with the file descriptor fildes which is not removed by a subsequent close() on that file descriptor. This reference is removed when there are no more mappings to the file.
来源：https://stackoverflow.com/questions/17490033/do-i-need-to-keep-a-file-open-after-calling-mmap-on-it