zsmalloc: skip chain size calculation for pow_of_2 classes

If a class size is power of 2 then it wastes no memory and the best
configuration is 1 physical page per-zspage.

Link: https://lkml.kernel.org/r/20230118005210.2814763-3-senozhatsky@chromium.orgSigned-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Acked-by: Minchan Kim <minchan@kernel.org>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/zsmalloc.c

@@ -2370,6 +2370,9 @@ static int calculate_zspage_chain_size(int class_size)
 	int i, min_waste = INT_MAX;
 	int chain_size = 1;
 
+	if (is_power_of_2(class_size))
+		return chain_size;
+
 	for (i = 1; i <= ZS_MAX_PAGES_PER_ZSPAGE; i++) {
 		int waste;