Rework madvise_cold_or_pageout_pte_range() to avoid splitting any large
folio that is fully and contiguously mapped in the pageout/cold vm range. 
This change means that large folios will be maintained all the way to swap
storage.  This both improves performance during swap-out, by eliding the
cost of splitting the folio, and sets us up nicely for maintaining the
large folio when it is swapped back in (to be covered in a separate
series).

Folios that are not fully mapped in the target range are still split, but
note that behavior is changed so that if the split fails for any reason
(folio locked, shared, etc) we now leave it as is and move to the next pte
in the range and continue work on the proceeding folios.  Previously any
failure of this sort would cause the entire operation to give up and no
folios mapped at higher addresses were paged out or made cold.  Given
large folios are becoming more common, this old behavior would have likely
lead to wasted opportunities.

While we are at it, change the code that clears young from the ptes to use
ptep_test_and_clear_young(), via the new mkold_ptes() batch helper
function.  This is more efficent than get_and_clear/modify/set, especially
for contpte mappings on arm64, where the old approach would require
unfolding/refolding and the new approach can be done in place.

Link: https://lkml.kernel.org/r/20240408183946.2991168-8-ryan.roberts@arm.comSigned-off-by: Ryan Roberts <ryan.roberts@arm.com>
Reviewed-by: Barry Song <v-songbaohua@oppo.com>
Acked-by: David Hildenbrand <david@redhat.com>
Cc: Barry Song <21cnbao@gmail.com>
Cc: Chris Li <chrisl@kernel.org>
Cc: Gao Xiang <xiang@kernel.org>
Cc: "Huang, Ying" <ying.huang@intel.com>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: Lance Yang <ioworker0@gmail.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Yang Shi <shy828301@gmail.com>
Cc: Yu Zhao <yuzhao@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>