Long-term get_user_pages() and truncate(): solved at last?

Technologies like RDMA benefit from the ability to map file-backed pages into memory. This benefit extends to persistent-memory devices, where the backing store for the file can be mapped directly without the need to go through the kernel's page cache. There is a fundamental conflict, though, between mapping a file's backing store directly and letting the filesystem code modify that file's on-disk layout, especially when the mapping is held in place for a long time (as RDMA is wont to do). The problem seems intractable, but there may yet be a solution in the form of this patch set (marked "V1,000,002") from Ira Weiny.

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