swap code uses these macros to size some of its array data structures
based on PMD_ORDER e.g. SWAPFILE_CLUSTER macro is used for this very
purpose.
Hence this patch makes the users of SWAPFILE_CLUSTER to use this macro value at
runtime and also modifies swap_table and swap_memcg_table which were earlier
using this macro for defining the number of table entries.

Signed-off-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
---
 mm/swap_table.h |  6 ++----
 mm/swapfile.c   | 17 ++++++++++++-----
 2 files changed, 14 insertions(+), 9 deletions(-)

diff --git a/mm/swap_table.h b/mm/swap_table.h
index e6613e62f8d0..90e2a7852300 100644
--- a/mm/swap_table.h
+++ b/mm/swap_table.h

@@ -8,16 +8,14 @@

 /* A typical flat array in each cluster as swap table */
 struct swap_table {
-       atomic_long_t entries[SWAPFILE_CLUSTER];
+       DECLARE_FLEX_ARRAY(atomic_long_t, entries);
 };

 /* For storing memcg private id */
 struct swap_memcg_table {
-       unsigned short id[SWAPFILE_CLUSTER];
+       DECLARE_FLEX_ARRAY(unsigned short, id);
 };

-#define SWP_TABLE_USE_PAGE (sizeof(struct swap_table) == PAGE_SIZE)
-
 /*
  * A swap table entry represents the status of a swap slot on a swap
  * (physical or virtual) device. The swap table in each cluster is a

diff --git a/mm/swapfile.c b/mm/swapfile.c
index 78b49b0658ad..4bf11c5b87eb 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c

@@ -129,6 +129,8 @@ static DEFINE_PER_CPU(struct percpu_swap_cluster, percpu_swap_cluster) = {
        .lock = INIT_LOCAL_LOCK(),
 };

+static bool swap_table_use_page __ro_after_init;