mm: change filecache reclaim policy for CMA [1/1]

mm: change filecache reclaim policy for CMA [1/1]

PD#SWPL-119

Problem:
High IOW usually happen when start playing 4K video. This
is because codec drvier will using large amount of memory
from CMA pool. And many filecache will be dropped after CMA
allocation finished without considering mapcount of each
file cache page.

Solution:
Check mapcount of filecache for each file pages. And migrate
them if they have high map count. High map count means this
file cache page is shared by many process.

Verify:
verified by ampere

Change-Id: I3e09437286f14a6cd9f7025566eb855dc9ca98d5
Signed-off-by: tao zeng <tao.zeng@amlogic.com>