mm: migrate: simplify __buffer_migrate_folio()

Patch series "mm: cleanup MIGRATE_SYNC_NO_COPY mode".

Commit 2916ecc0 ("mm/migrate: new migrate mode MIGRATE_SYNC_NO_COPY")
introduce a new MIGRATE_SYNC_NO_COPY mode to allow to offload the copy to
a device DMA engine, which is only used __migrate_device_pages() to decide
whether or not copy the old page, and the MIGRATE_SYNC_NO_COPY mode only
used in hmm, a easy way is just to call the folio_migrate_mapping() and
folio_migrate_flags(), which help to remove the MIGRATE_SYNC_NO_COPY mode.


This patch (of 5):

Use filemap_migrate_folio() helper to simplify __buffer_migrate_folio().

Link: https://lkml.kernel.org/r/20240524052843.182275-1-wangkefeng.wang@huawei.com
Link: https://lkml.kernel.org/r/20240524052843.182275-2-wangkefeng.wang@huawei.comSigned-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Vishal Moola (Oracle) <vishal.moola@gmail.com>
Reviewed-by: Miaohe Lin <linmiaohe@huawei.com>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Benjamin LaHaise <bcrl@kvack.org>
Cc: David Hildenbrand <david@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jérôme Glisse <jglisse@redhat.com>
Cc: Jiaqi Yan <jiaqiyan@google.com>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Naoya Horiguchi <nao.horiguchi@gmail.com>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/migrate.c

@@ -777,24 +777,16 @@ static int __buffer_migrate_folio(struct address_space *mapping,
 		}
 	}
 
-	rc = folio_migrate_mapping(mapping, dst, src, 0);
+	rc = filemap_migrate_folio(mapping, dst, src, mode);
 	if (rc != MIGRATEPAGE_SUCCESS)
 		goto unlock_buffers;
 
-	folio_attach_private(dst, folio_detach_private(src));
-
 	bh = head;
 	do {
 		folio_set_bh(bh, dst, bh_offset(bh));
 		bh = bh->b_this_page;
 	} while (bh != head);
 
-	if (mode != MIGRATE_SYNC_NO_COPY)
-		folio_migrate_copy(dst, src);
-	else
-		folio_migrate_flags(dst, src);
-
-	rc = MIGRATEPAGE_SUCCESS;
 unlock_buffers:
 	if (check_refs)
 		spin_unlock(&mapping->i_private_lock);