mm/madvise: thread VMA range state through madvise_behavior

mm/madvise: thread VMA range state through madvise_behavior

Rather than updating start and a confusing local parameter 'tmp' in
madvise_walk_vmas(), instead store the current range being operated upon
in the struct madvise_behavior helper object in a range pair and use this
consistently in all operations.

This makes it clearer what is going on and opens the door to further
cleanup now we store state regarding what is currently being operated upon
here.

Link: https://lkml.kernel.org/r/518480ceb48553d3c280bc2b0b5e77bbad840147.1750433500.git.lorenzo.stoakes@oracle.com
Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Reviewed-by: SeongJae Park <sj@kernel.org>
Reviewed-by: Barry Song <baohua@kernel.org>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Dev Jain <dev.jain@arm.com>
Cc: Jann Horn <jannh@google.com>
Cc: Lance Yang <ioworker0@gmail.com>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Mariano Pache <npache@redhat.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>