ksm: no debug in page_dup_rmap()

ksm: no debug in page_dup_rmap()

page_dup_rmap(), used on each mapped page when forking, was originally
just an inline atomic_inc of mapcount.  2.6.22 added CONFIG_DEBUG_VM
out-of-line checks to it, which would need to be ever-so-slightly
complicated to allow for the PageKsm() we're about to define.

But I think these checks never caught anything.  And if it's coding errors
we're worried about, such checks should be in page_remove_rmap() too, not
just when forking; whereas if it's pagetable corruption we're worried
about, then they shouldn't be limited to CONFIG_DEBUG_VM.

Oh, just revert page_dup_rmap() to an inline atomic_inc of mapcount.

Signed-off-by: Hugh Dickins <[email protected]>
Signed-off-by: Chris Wright <[email protected]>
Signed-off-by: Izik Eidus <[email protected]>
Cc: Nick Piggin <[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]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>