percpu: add first_bit to keep track of the first free in the bitmap

This patch adds first_bit to keep track of the first free bit in the
bitmap. This hint helps prevent scanning of fully allocated blocks.

Signed-off-by: Dennis Zhou <dennisszhou@gmail.com>
Reviewed-by: Josef Bacik <jbacik@fb.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
diff --git a/mm/percpu-stats.c b/mm/percpu-stats.c
index ad03d73..6142484e 100644
--- a/mm/percpu-stats.c
+++ b/mm/percpu-stats.c
@@ -121,6 +121,7 @@ static void chunk_map_stats(struct seq_file *m, struct pcpu_chunk *chunk,
 	P("nr_alloc", chunk->nr_alloc);
 	P("max_alloc_size", chunk->max_alloc_size);
 	P("empty_pop_pages", chunk->nr_empty_pop_pages);
+	P("first_bit", chunk->first_bit);
 	P("free_bytes", chunk->free_bytes);
 	P("contig_bytes", chunk->contig_bits * PCPU_MIN_ALLOC_SIZE);
 	P("sum_frag", sum_frag);