Messages in this thread | | | Date | Fri, 7 Jul 2017 13:23:24 +0300 | From | "Kirill A. Shutemov" <> | Subject | Re: [RFC PATCH 1/1] mm/mremap: add MREMAP_MIRROR flag for existing mirroring functionality |
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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
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