gpu: ion: Reduce allocation time from system heap

If we are under heavy memory pressure the shrinker might be running on
the system heap. This causes contention with the page pool lock when we
try to allocate from system heap. To ensure that allocations aren't
slowed down by having to wait for the page pool mutex we will just try
to get the mutex. If we are unsuccessful we just bypass the pool
altogether.

Signed-off-by: Olav Haugan <ohaugan@codeaurora.org>
Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>
gpu: ion: fix overflow and list bugs in system heap

Fix a few bugs in ion_system_heap:

Initialize the list node in the info block.

Don't store size_remaining in a signed long, allocating >2GB
could overflow, resulting in a call to sg_alloc_table with
nents=0 which panics.  alloc_largest_available will never
return a block larger than size_remanining, so it can never
go negative.

Limit a single allocation to half of all memory.  Prevents a
large allocation from taking down the whole system.

Signed-off-by: Colin Cross <ccross@android.com>
Git-commit: c69de844c80884167bb42243b36498dde81eebf6
Git-repo: http://android.googlesource.com/kernel/common/
[mitchelh@codeaurora.org: we already had the signed long fix]
Signed-off-by: Mitchel Humpherys <mitchelh@codeaurora.org>
Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>