resource: merge resources on a node when hot-adding memory

When hot-removing memory release_mem_region_adjustable() splits
iomem resources if they are not the exact size of the memory being
hot-deleted. Adding this memory back to the kernel adds a new
resource.

Eg a node has memory 0x0 - 0xfffffffff. Offlining and hot-removing
1GB from 0xf40000000 results in the single resource 0x0-0xfffffffff being
split into two resources: 0x0-0xf3fffffff and 0xf80000000-0xfffffffff.

When we hot-add the memory back we now have three resources:
0x0-0xf3fffffff, 0xf40000000-0xf7fffffff, and 0xf80000000-0xfffffffff.

Now if we try to remove some memory that overlaps these resources,
like 2GB from 0xf40000000, release_mem_region_adjustable() fails as it
expects the chunk of memory to be within the boundaries of a single
resource.

This patch adds a function request_resource_and_merge(). This is called
instead of request_resource_conflict() when registering a resource in
add_memory(). It calls request_resource_conflict() and if hot-removing is
enabled (if it isn't we won't get resource fragmentation) we attempt to
merge contiguous resources on the node.

Link: http://lkml.kernel.org/r/20180809025409.31552-1-rashmica.g@gmail.com
Signed-off-by: Rashmica Gupta <rashmica.g@gmail.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Reviewed-by: Mike Rapoport <rppt@linux.vnet.ibm.com>
Cc: Toshi Kani <toshi.kani@hpe.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Borislav Petkov <bp@suse.de>
Cc: Brijesh Singh <brijesh.singh@amd.com>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Yaowei Bai <baiyaowei@cmss.chinamobile.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Mathieu Malaterre <malat@debian.org>
Cc: Bjorn Helgaas <bhelgaas@google.com>
Cc: <yasu.isimatu@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>

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