I'm trying to find out how to remap memory-mapped files on a Mac (when I want to expand the available space).
I see our friends in the Linux world have mremap but I can find no such function in the headers on my Mac. /Developer/SDKs/MacOSX10.6.sdk/usr/include/sys/mman.h has the following:
mmapmprotectmsyncmunlockmunmapmremapman mremap confirms my fears.
I'm currently having to munmap and mmmap if I want to resize the size of the mapped file, which involves invalidating all the loaded pages. There must be a better way. Surely?
I'm trying to write code that will work on Mac OS X and Linux. I could settle for a macro to use the best function in each case if I had to but I'd rather do it properly.
You can ftruncate the file to a large size (creating a hole) and mmap all of it. If the file is persistent I recommend filling the hole with write calls rather than by writing in the mapping, as otherwise the file's blocks may get unnecessarily fragmented on the disk.