On mobile devices, failure to allocate from a CMA area constitutes a functional failure. Sometimes during CMA allocations, we have observed that pages in a CMA area allocated through alloc_pages(), that we're trying to migrate away to make room for a CMA allocation, are temporarily pinned. This temporary pinning can occur when a process that owns the pinned page is being forked (the example is explained further in the commit text). This patch addresses this issue by adding a sleep-and-retry loop in cma_alloc() . There's another example we know of similar to the above that occurs during exit_mmap() (in zap_pte_range() specifically), but I need to determine if this is still relevant today.
