block: bdev: blockdev page cache is movable

While inspecting page blocks for the type of pages in them, I noticed
a large number of blockdev cache in unmovable blocks. However, these
pages are actually on the LRU, and their mapping has a .migrate_folio
callback; they can be reclaimed and compacted as necessary.

Put them into movable blocks, so they don't cause pollution, and
subsequent proliferation, of unmovable blocks.

Signed-off-by: Johannes Weiner <[email protected]>

block/bdev.c

@@ -488,7 +488,7 @@ struct block_device *bdev_alloc(struct gendisk *disk, u8 partno)
 	inode->i_mode = S_IFBLK;
 	inode->i_rdev = 0;
 	inode->i_data.a_ops = &def_blk_aops;
-	mapping_set_gfp_mask(&inode->i_data, GFP_USER);
+	mapping_set_gfp_mask(&inode->i_data, GFP_USER|__GFP_MOVABLE);
 
 	bdev = I_BDEV(inode);
 	mutex_init(&bdev->bd_fsfreeze_mutex);