mm: introduce vma_merge_struct and abstract vma_merge(),vma_modify()

mm: introduce vma_merge_struct and abstract vma_merge(),vma_modify()

Rather than passing around huge numbers of parameters to numerous helper
functions, abstract them into a single struct that we thread through the
operation, the vma_merge_struct ('vmg').

Adjust vma_merge() and vma_modify() to accept this parameter, as well as
predicate functions can_vma_merge_before(), can_vma_merge_after(), and the
vma_modify_...() helper functions.

Also introduce VMG_STATE() and VMG_VMA_STATE() helper macros to allow for
easy vmg declaration.

We additionally remove the requirement that vma_merge() is passed a VMA
object representing the candidate new VMA.  Previously it used this to
obtain the mm_struct, file and anon_vma properties of the proposed range
(a rather confusing state of affairs), which are now provided by the vmg
directly.

We also remove the pgoff calculation previously performed vma_modify(),
and instead calculate this in VMG_VMA_STATE() via the vma_pgoff_offset()
helper.

Link: https://lkml.kernel.org/r/a955aad09d81329f6fbeb636b2dd10cde7b73dab.1725040657.git.lorenzo.stoakes@oracle.com
Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Reviewed-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Mark Brown <broonie@kernel.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Bert Karwatzki <spasswolf@web.de>
Cc: Jeff Xu <jeffxu@chromium.org>
Cc: Jiri Olsa <olsajiri@gmail.com>
Cc: Kees Cook <kees@kernel.org>
Cc: Lorenzo Stoakes <lstoakes@gmail.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: "Paul E. McKenney" <paulmck@kernel.org>
Cc: Paul Moore <paul@paul-moore.com>
Cc: Sidhartha Kumar <sidhartha.kumar@oracle.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>