mm/percpu: micro-optimize pcpu_is_populated()

bitmap_next_clear_region() calls find_next_zero_bit() and find_next_bit()
sequentially to find a range of clear bits. In case of pcpu_is_populated()
there's a chance to return earlier if bitmap has all bits set.

Signed-off-by: Yury Norov <yury.norov@gmail.com>
Tested-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Acked-by: Dennis Zhou <dennis@kernel.org>

Author: YuryNorov

mm/percpu.c

@@ -1070,17 +1070,18 @@ static void pcpu_block_update_hint_free(struct pcpu_chunk *chunk, int bit_off,
 static bool pcpu_is_populated(struct pcpu_chunk *chunk, int bit_off, int bits,
 			      int *next_off)
 {
-	unsigned int page_start, page_end, rs, re;
+	unsigned int start, end;
 
-	page_start = PFN_DOWN(bit_off * PCPU_MIN_ALLOC_SIZE);
-	page_end = PFN_UP((bit_off + bits) * PCPU_MIN_ALLOC_SIZE);
+	start = PFN_DOWN(bit_off * PCPU_MIN_ALLOC_SIZE);
+	end = PFN_UP((bit_off + bits) * PCPU_MIN_ALLOC_SIZE);
 
-	rs = page_start;
-	bitmap_next_clear_region(chunk->populated, &rs, &re, page_end);
-	if (rs >= page_end)
+	start = find_next_zero_bit(chunk->populated, end, start);
+	if (start >= end)
 		return true;
 
-	*next_off = re * PAGE_SIZE / PCPU_MIN_ALLOC_SIZE;
+	end = find_next_bit(chunk->populated, end, start + 1);
+
+	*next_off = end * PAGE_SIZE / PCPU_MIN_ALLOC_SIZE;
 	return false;
 }