ksm: define MADV_MERGEABLE and MADV_UNMERGEABLE

The out-of-tree KSM used ioctls on fds cloned from /dev/ksm to register a
memory area for merging: we prefer now to use an madvise(2) interface.

This patch just defines MADV_MERGEABLE (to tell KSM it may merge pages in
this area found identical to pages in other mergeable areas) and
MADV_UNMERGEABLE (to undo that).

Most architectures use asm-generic, but alpha, mips, parisc, xtensa need
their own definitions: included here for mmotm convenience, but we'll
probably want to split this and feed pieces to arch maintainers.

Based upon earlier patches by Chris Wright and Izik Eidus.

Signed-off-by: Hugh Dickins <[email protected]>
Signed-off-by: Chris Wright <[email protected]>
Signed-off-by: Izik Eidus <[email protected]>
Cc: Michael Kerrisk <[email protected]>
Cc: Richard Henderson <[email protected]>
Cc: Ivan Kokshaysky <[email protected]>
Cc: Ralf Baechle <[email protected]>
Cc: Kyle McMartin <[email protected]>
Cc: Helge Deller <[email protected]>
Cc: Chris Zankel <[email protected]>
Cc: Andrea Arcangeli <[email protected]>
Cc: Rik van Riel <[email protected]>
Cc: Wu Fengguang <[email protected]>
Cc: Balbir Singh <[email protected]>
Cc: Hugh Dickins <[email protected]>
Cc: KAMEZAWA Hiroyuki <[email protected]>
Cc: Lee Schermerhorn <[email protected]>
Cc: Avi Kivity <[email protected]>
Cc: Nick Piggin <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

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