mm, mempool: poison elements backed by page allocator

mm, mempool: poison elements backed by page allocator

Elements backed by the slab allocator are poisoned when added to a
mempool's reserved pool.

It is also possible to poison elements backed by the page allocator
because the mempool layer knows the allocation order.

This patch extends mempool element poisoning to include memory backed by
the page allocator.

This is only effective for configs with CONFIG_DEBUG_SLAB or
CONFIG_SLUB_DEBUG_ON.

Signed-off-by: David Rientjes <rientjes@google.com>
Cc: Dave Kleikamp <shaggy@kernel.org>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Sebastian Ott <sebott@linux.vnet.ibm.com>
Cc: Mikulas Patocka <mpatocka@redhat.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>