mem: Handle the case when kernel doesn't support dirty track reset
mem: Handle the case when kernel doesn't support dirty track reset

Signed-off-by: Pavel Emelyanov <c9a32589e048e044184536f7ac71ef92fe82df3e@virtuozzo.com>
Acked-by: Andrew Vagin <74c05afa918858348d6db8037d82fa8124870113@virtuozzo.com>
Tested-by: Adrian Reber <a1b909ec1cc11cce40c28d3640eab600e582f833@lisas.de>

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