Memory mirroring for a ring buffer on Linux

Question

I use an anonymous mmap to allocate a giant chunk of memory. There are several contiguous pages in this that I'd like to turn into a ring buffer, using virtual memory mirroring.

This example on Wikipedia shows what I'm meaning by virtual memory mirroring.

Say the first 14 blocks below are the pages in my giant chunk. I'd like to virtually map pages 6 and 7 to another two consecutive locations.

[0][1][2][3][4][5][6][7][8][9][10][11][12][13].......[6][7][6][7]

Mike Ash gives a rundown of what I want to do, but using mach specific APIs.

How can this be done on Linux?

Answer 1

This is not possible to achieve with anonymous mappings. You can, however, use memfd_create(2) or create a temporary file on tmpfs (so that it won't ever be stored to disk, except by "swapping") and do shared mappings on that file descriptor, adjacent to each other.

remap_file_pages(2) is just a performance hack and not any more powerful than classic mmap/mremap calls, and it can't operate on anonymous mappings either.

Related: Linux mremap without freeing the old mapping?