mm/swapfile.c: simplify the calculation of n_goal

Use min3() to simplify the comparison and make it more self-explaining.
Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Hugh Dickins <hughd@google.com>
Link: http://lkml.kernel.org/r/20200325220309.9803-1-richard.weiyang@gmail.comSigned-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/swapfile.c

@@ -994,11 +994,7 @@ int get_swap_pages(int n_goal, swp_entry_t swp_entries[], int entry_size)
 	if (avail_pgs <= 0)
 		goto noswap;
 
-	if (n_goal > SWAP_BATCH)
-		n_goal = SWAP_BATCH;
-
-	if (n_goal > avail_pgs)
-		n_goal = avail_pgs;
+	n_goal = min3((long)n_goal, (long)SWAP_BATCH, avail_pgs);
 
 	atomic_long_sub(n_goal * size, &nr_swap_pages);