mm: workingset: define macro WORKINGSET_SHIFT

The magic number 1 is used in several places in workingset.c.  Define a
macro WORKINGSET_SHIFT for it to improve code readability.

Link: https://lkml.kernel.org/r/20210624122307.1759342-1-linmiaohe@huawei.comSigned-off-by: Miaohe Lin <linmiaohe@huawei.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/workingset.c

@@ -168,8 +168,10 @@
  * refault distance will immediately activate the refaulting page.
  */
 
+#define WORKINGSET_SHIFT 1
 #define EVICTION_SHIFT	((BITS_PER_LONG - BITS_PER_XA_VALUE) +	\
-			 1 + NODES_SHIFT + MEM_CGROUP_ID_SHIFT)
+			 WORKINGSET_SHIFT + NODES_SHIFT + \
+			 MEM_CGROUP_ID_SHIFT)
 #define EVICTION_MASK	(~0UL >> EVICTION_SHIFT)
 
 /*
@@ -189,7 +191,7 @@ static void *pack_shadow(int memcgid, pg_data_t *pgdat, unsigned long eviction,
 	eviction &= EVICTION_MASK;
 	eviction = (eviction << MEM_CGROUP_ID_SHIFT) | memcgid;
 	eviction = (eviction << NODES_SHIFT) | pgdat->node_id;
-	eviction = (eviction << 1) | workingset;
+	eviction = (eviction << WORKINGSET_SHIFT) | workingset;
 
 	return xa_mk_value(eviction);
 }
@@ -201,8 +203,8 @@ static void unpack_shadow(void *shadow, int *memcgidp, pg_data_t **pgdat,
 	int memcgid, nid;
 	bool workingset;
 
-	workingset = entry & 1;
-	entry >>= 1;
+	workingset = entry & ((1UL << WORKINGSET_SHIFT) - 1);
+	entry >>= WORKINGSET_SHIFT;
 	nid = entry & ((1UL << NODES_SHIFT) - 1);
 	entry >>= NODES_SHIFT;
 	memcgid = entry & ((1UL << MEM_CGROUP_ID_SHIFT) - 1);