mm: change count_objcg_event() to count_objcg_events() for batch event updates

mm: change count_objcg_event() to count_objcg_events() for batch event updates

With the introduction of zswap_store() swapping out large folios, we need
to efficiently update the objcg's memcg events once per successfully
stored folio.  For instance, the 'ZSWPOUT' event needs to be incremented
by folio_nr_pages().

To facilitate this, the existing count_objcg_event() API is modified to be
count_objcg_events() that additionally accepts a count parameter.  The
only existing calls to count_objcg_event() are in zswap.c - these have
been modified to call count_objcg_events() with a count of 1.

Link: https://lkml.kernel.org/r/20241001053222.6944-5-kanchana.p.sridhar@intel.com
Signed-off-by: Kanchana P Sridhar <kanchana.p.sridhar@intel.com>
Acked-by: Yosry Ahmed <yosryahmed@google.com>
Reviewed-by: Nhat Pham <nphamcs@gmail.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: Chengming Zhou <chengming.zhou@linux.dev>
Cc: "Huang, Ying" <ying.huang@intel.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Usama Arif <usamaarif642@gmail.com>
Cc: Wajdi Feghali <wajdi.k.feghali@intel.com>
Cc: "Zou, Nanhai" <nanhai.zou@intel.com>
Cc: Barry Song <21cnbao@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>