ceph: Remove ceph_writepage()

Ceph already has a writepages operation which is preferred over writepage
in all situations except for page migration.  By adding a migrate_folio
operation, there will be no situations in which ->writepage should
be called.  filemap_migrate_folio() is an appropriate operation to use
because the ceph data stored in folio->private does not contain any
reference to the memory address of the folio.

Signed-off-by: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Link: https://lore.kernel.org/r/20250217185119.430193-2-willy@infradead.org
Tested-by: Viacheslav Dubeyko <Slava.Dubeyko@ibm.com>
Reviewed-by: Viacheslav Dubeyko <Slava.Dubeyko@ibm.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>

Author: Matthew Wilcox (Oracle)

fs/ceph/addr.c

@@ -852,32 +852,6 @@ static int writepage_nounlock(struct page *page, struct writeback_control *wbc)
 	return err;
 }
 
-static int ceph_writepage(struct page *page, struct writeback_control *wbc)
-{
-	int err;
-	struct inode *inode = page->mapping->host;
-	BUG_ON(!inode);
-	ihold(inode);
-
-	if (wbc->sync_mode == WB_SYNC_NONE &&
-	    ceph_inode_to_fs_client(inode)->write_congested) {
-		redirty_page_for_writepage(wbc, page);
-		return AOP_WRITEPAGE_ACTIVATE;
-	}
-
-	folio_wait_private_2(page_folio(page)); /* [DEPRECATED] */
-
-	err = writepage_nounlock(page, wbc);
-	if (err == -ERESTARTSYS) {
-		/* direct memory reclaimer was killed by SIGKILL. return 0
-		 * to prevent caller from setting mapping/page error */
-		err = 0;
-	}
-	unlock_page(page);
-	iput(inode);
-	return err;
-}
-
 /*
  * async writeback completion handler.
  *
@@ -1944,14 +1918,14 @@ static int ceph_write_end(struct file *file, struct address_space *mapping,
 const struct address_space_operations ceph_aops = {
 	.read_folio = netfs_read_folio,
 	.readahead = netfs_readahead,
-	.writepage = ceph_writepage,
 	.writepages = ceph_writepages_start,
 	.write_begin = ceph_write_begin,
 	.write_end = ceph_write_end,
 	.dirty_folio = ceph_dirty_folio,
 	.invalidate_folio = ceph_invalidate_folio,
 	.release_folio = netfs_release_folio,
 	.direct_IO = noop_direct_IO,
+	.migrate_folio = filemap_migrate_folio,
 };
 
 static void ceph_block_sigs(sigset_t *oldset)