We record start pfn of last isolated page block with last_migrated_pfn. And
then:

1. We check if we mark the page block skip for exclusive access in
   isolate_migratepages_block by test if next migrate pfn is still in last
   isolated page block.  If so, we will set finish_pageblock to do the
   rescan.

2. We check if a full cc->order block is scanned by test if last scan
   range passes the cc->order block boundary.  If so, we flush the pages
   were freed.

We treat cc->migrate_pfn before isolate_migratepages as the start pfn of
last isolated page range.  However, we always align migrate_pfn to page
block or move to another page block in fast_find_migrateblock or in
linearly scan forward in isolate_migratepages before do page isolation in
isolate_migratepages_block.

Update last_migrated_pfn with pageblock_start_pfn(cc->migrate_pfn - 1)
after scan to correctly set start pfn of last isolated page range. To
avoid that:

1. Miss a rescan with finish_pageblock set as last_migrate_pfn does
   not point to right pageblock and the migrate will not be in pageblock
   of last_migrate_pfn as it should be.

2. Wrongly issue flush by test cc->order block boundary with wrong
   last_migrate_pfn.

Link: https://lkml.kernel.org/r/20230804110454.2935878-3-shikemeng@huaweicloud.comSigned-off-by: Kemeng Shi <shikemeng@huaweicloud.com>
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>