backport lowmemorykiller.c from codeaurora mem-3.4
adapted by mrg666
Note: CMA is not backported but kernel can now declare that there is no CMA
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android/lowmemorykiller: Wait for memory to be freed

The memory reclaim code needs to give time to the system to
return the memory from a killed process otherwise the memory
reclaim code could run continuously, in multiple threads,
which could starve both the watchdog thread and the thread
which is responsible for returning the memory from the
killed process.

Change-Id: Ieded4bfe038ca936247fa4b638070e979b02eaa1
CRs-fixed: 447740
Signed-off-by: Liam Mark <lmark@codeaurora.org>

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android/lowmemorykiller: Ignore tasks with freed mm

A killed task can stay in the task list long after its
memory has been returned to the system, therefore
ignore any tasks whose mm struct has been freed.

Change-Id: I76394b203b4ab2312437c839976f0ecb7b6dde4e
CRs-fixed: 450383
Signed-off-by: Liam Mark <lmark@codeaurora.org>

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android/lowmemorykiller: Only consider gfp_mask free pages

In certain memory configurations there can be a large number of
CMA pages which are not suitable to satisfy certain memory
requests.
This large number of unsuitable pages can cause the
lowmemorykiller to not kill any tasks because the
lowmemorykiller counts all free pages.

In order to ensure the lowmemorykiller properly evaluates the
free memory only count the free pages which are suitable for
satisfying the memory request.

Change-Id: Iabc3bebc54be9dec7fcbffb94a2fbf18dd684669
Signed-off-by: Liam Mark <lmark@codeaurora.org>
Signed-off-by: Laura Abbott <lauraa@codeaurora.org>