vmscan: add a vmscan event for reclaim_pages

vmscan: add a vmscan event for reclaim_pages

reclaim_folio_list uses a dummy reclaim_stat and is not being used.  To
know the memory stat, add a new trace event.  This is useful how how many
pages are not reclaimed or why.

This is an example:

mm_vmscan_reclaim_pages: nid=0 nr_scanned=112 nr_reclaimed=112 nr_dirty=0 nr_writeback=0 nr_congested=0 nr_immediate=0 nr_activate_anon=0 nr_activate_file=0 nr_ref_keep=0 nr_unmap_fail=0

Currently reclaim_folio_list is only called by reclaim_pages, and
reclaim_pages is used by damon and madvise.  In the latest Android,
reclaim_pages is also used by shmem to reclaim all pages in a
address_space.

[jaewon31.kim@samsung.com: use sc.nr_scanned rather than new counting]
Link: https://lkml.kernel.org/r/20241016143227.961162-1-jaewon31.kim@samsung.com
Link: https://lkml.kernel.org/r/20241011124928.1224813-1-jaewon31.kim@samsung.com
Signed-off-by: Jaewon Kim <jaewon31.kim@samsung.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Jaewon Kim <jaewon31.kim@samsung.com>
Cc: Kalesh Singh <kaleshsingh@google.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: SeongJae Park <sj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>