Does this mean that I have to msync multiple mmap'ed chunks in order to batch write? For example

    msync(ptr1, len1)
    msync(ptr2, len2)
    msync(ptr3, len3)

Where [ptr1, ptr1+len1], [ptr2, ptr2+len2], ... are the chunks within a big mmap'ed region where changes occur and need to be written to disk for persistence.

Or do I just msync the whole region then hope and pray that the OS will do the right thing?