This can be used to estimate the size of the data cache slice that can be
used by one CPU under ideal circumstances.  Both DATA caches and UNIFIED
caches are used in calculation.  So, the users need to consider the impact
of the code cache usage.

Because the cache inclusive/non-inclusive information isn't available now,
we just use the size of the per-CPU slice of LLC to make the result more
predictable across architectures.  This may be improved when more cache
information is available in the future.

A brute-force algorithm to iterate all online CPUs is used to avoid to
allocate an extra cpumask, especially in offline callback.

Link: https://lkml.kernel.org/r/20231016053002.756205-3-ying.huang@intel.comSigned-off-by: "Huang, Ying" <ying.huang@intel.com>
Acked-by: Mel Gorman <mgorman@techsingularity.net>
Cc: Sudeep Holla <sudeep.holla@arm.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: David Hildenbrand <david@redhat.com>
Cc: Johannes Weiner <jweiner@redhat.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Christoph Lameter <cl@linux.com>
Cc: Arjan van de Ven <arjan@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>