Currently, page block type conversion during fallbacks, atomic
reservations and isolation can strand various amounts of free pages on
incorrect freelists.

For example, fallback stealing moves free pages in the block to the new
type's freelists, but then may not actually claim the block for that type
if there aren't enough compatible pages already allocated.

In all cases, free page moving might fail if the block straddles more than
one zone, in which case no free pages are moved at all, but the block type
is changed anyway.

This is detrimental to type hygiene on the freelists.  It encourages
incompatible page mixing down the line (ask for one type, get another) and
thus contributes to long-term fragmentation.

Split the process into a proper transaction: check first if conversion
will happen, then try to move the free pages, and only if that was
successful convert the block to the new type.

[baolin.wang@linux.alibaba.com: fix allocation failures with CONFIG_CMA]
  Link: https://lkml.kernel.org/r/a97697e0-45b0-4f71-b087-fdc7a1d43c0e@linux.alibaba.com
Link: https://lkml.kernel.org/r/20240320180429.678181-7-hannes@cmpxchg.orgSigned-off-by: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Tested-by: "Huang, Ying" <ying.huang@intel.com>
Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
Tested-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>