mm: fix process_vm_rw page counts
1. There is a "-1" missing in the page number calculation in
process_vm_rw_core. While this can't break anything, it can cause
unnecessary allocations in certain cases:
Consider handling an iovec ranging over PVM_MAX_PP_ARRAY_COUNT pages
that is also aligned to a page boundary. While pp_stack could hold
references to such an amount of pinned pages, nr_pages yields
(PVM_MAX_PP_ARRAY + 1) in process_vm_rw_core. Consequently, a larger
buffer is allocated with kmalloc for no reason.
For any page boundary aligned iovec that is a multiple of PAGE_SIZE
and larger than PVM_MAX_PP_ARRAY_COUNT pages, nr_pages will be too big
by 1 and thus kmalloc allocates excess space for one more pointer.
2. max_pages_per_loop is constant and there is no reason to have it as
a variable. A macro does the job just fine and saves memory.
3. Replaced "sizeof(struct pages *)" with "sizeof(struct page *)" to
have matching types for allocation and prevent confusion.
Link: https://lkml.kernel.org/r/20231111184859.44264-1-yjnworkstation@gmail.com
Signed-off-by: York Jasper Niebuhr <yjnworkstation@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>