mm/swapfile.c: classify SWAP_MAP_XXX to make it more readable

swap_info_struct->swap_map[] encodes some flag and count. And to
do some condition check, it also introduces some special values.

Currently those macros are defined with some magic order, which makes
audience hard to understand the exact meaning.

This patch split those macros into three categories:

    flag
    special value for first swap_map
    special value for continued swap_map

May this help audiences a little.

[akpm@linux-foundation.org: tweak capitalization in comments]
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>
Link: http://lkml.kernel.org/r/20200501015259.32237-1-richard.weiyang@gmail.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/include/linux/swap.h b/include/linux/swap.h
index e1bbf7a16b2767ab08d53f9b297d5c1c87cc992f..873bf5206afbbc78999ecd7f2f690d807726e0cd 100644 (file)
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -183,12 +183,17 @@ enum {
 #define SWAP_CLUSTER_MAX 32UL
 #define COMPACT_CLUSTER_MAX SWAP_CLUSTER_MAX
 
-#define SWAP_MAP_MAX   0x3e    /* Max duplication count, in first swap_map */
-#define SWAP_MAP_BAD   0x3f    /* Note pageblock is bad, in first swap_map */
+/* Bit flag in swap_map */
 #define SWAP_HAS_CACHE 0x40    /* Flag page is cached, in first swap_map */
-#define SWAP_CONT_MAX  0x7f    /* Max count, in each swap_map continuation */
-#define COUNT_CONTINUED        0x80    /* See swap_map continuation for full count */
-#define SWAP_MAP_SHMEM 0xbf    /* Owned by shmem/tmpfs, in first swap_map */
+#define COUNT_CONTINUED        0x80    /* Flag swap_map continuation for full count */
+
+/* Special value in first swap_map */
+#define SWAP_MAP_MAX   0x3e    /* Max count */
+#define SWAP_MAP_BAD   0x3f    /* Note page is bad */
+#define SWAP_MAP_SHMEM 0xbf    /* Owned by shmem/tmpfs */
+
+/* Special value in each swap_map continuation */
+#define SWAP_CONT_MAX  0x7f    /* Max count */
 
 /*
  * We use this to track usage of a cluster. A cluster is a block of swap disk