radix tree test suite: add kmem_cache_set_non_kernel()

radix tree test suite: add kmem_cache_set_non_kernel()

kmem_cache_set_non_kernel() is a mechanism to allow a certain number of
kmem_cache_alloc requests to succeed even when GFP_KERNEL is not set in
the flags.  This functionality allows for testing different paths though
the code.

Link: https://lkml.kernel.org/r/20220822150128.1562046-4-Liam.Howlett@oracle.com
Signed-off-by: Liam R. Howlett <Liam.Howlett@Oracle.com>
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: David Howells <dhowells@redhat.com>
Cc: SeongJae Park <sj@kernel.org>
Cc: Sven Schnelle <svens@linux.ibm.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Will Deacon <will@kernel.org>
Cc: Yu Zhao <yuzhao@google.com>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>