percpu: manage chunks based on contig_bits instead of free_bytes

When a chunk becomes fragmented, it can end up having a large number of
small allocation areas free. The free_bytes sorting of chunks leads to
unnecessary checking of chunks that cannot satisfy the allocation.
Switch to contig_bits sorting to prevent scanning chunks that may not be
able to service the allocation request.
Signed-off-by: Dennis Zhou <dennis@kernel.org>
Reviewed-by: Peng Fan <peng.fan@nxp.com>

mm/percpu.c

@@ -234,7 +234,7 @@ static int pcpu_chunk_slot(const struct pcpu_chunk *chunk)
 	if (chunk->free_bytes < PCPU_MIN_ALLOC_SIZE || chunk->contig_bits == 0)
 		return 0;
 
-	return pcpu_size_to_slot(chunk->free_bytes);
+	return pcpu_size_to_slot(chunk->contig_bits * PCPU_MIN_ALLOC_SIZE);
 }
 
 /* set the pointer to a chunk in a page struct */