On Thu, Jul 06, 2017 at 09:17:26AM -0700, Mike Kravetz wrote: > The mremap system call has the ability to 'mirror' parts of an existing > mapping. To do so, it creates a new mapping that maps the same pages as > the original mapping, just at a different virtual address. This > functionality has existed since at least the 2.6 kernel. > > This patch simply adds a new flag to mremap which will make this > functionality part of the API. It maintains backward compatibility with > the existing way of requesting mirroring (old_size == 0). > > If this new MREMAP_MIRROR flag is specified, then new_size must equal > old_size. In addition, the MREMAP_MAYMOVE flag must be specified.
The patch breaks important invariant that anon page can be mapped into a process only once. What is going to happen to mirrored after CoW for instance? In my opinion, it shouldn't be allowed for anon/private mappings at least. And with this limitation, I don't see much sense in the new interface -- just create mirror by mmap()ing the file again. -- Kirill A. Shutemov
