swap_info: swap_map of chars not shorts

Halve the vmalloc'ed swap_map array from unsigned shorts to unsigned
chars: it's still very unusual to reach a swap count of 126, and the
next patch allows it to be extended indefinitely.

Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Rik van Riel <riel@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 23 insertions, 17 deletions

diff --git a/mm/swapfile.c b/mm/swapfile.c
index 52497490a7ca..c0d7b9ed0c16 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -53,7 +53,7 @@ static struct swap_info_struct *swap_info[MAX_SWAPFILES];
 
 static DEFINE_MUTEX(swapon_mutex);
 
-static inline int swap_count(unsigned short ent)
+static inline unsigned char swap_count(unsigned char ent)
 {
         return ent & ~SWAP_HAS_CACHE;
 }
@@ -203,7 +203,7 @@ static int wait_for_discard(void *word)
 #define LATENCY_LIMIT           256
 
 static inline unsigned long scan_swap_map(struct swap_info_struct *si,
-                                          unsigned short usage)
+                                          unsigned char usage)
 {
         unsigned long offset;
         unsigned long scan_base;
@@ -531,12 +531,12 @@ out:
         return NULL;
 }
 
-static unsigned short swap_entry_free(struct swap_info_struct *p,
-                           swp_entry_t entry, unsigned short usage)
+static unsigned char swap_entry_free(struct swap_info_struct *p,
+                                     swp_entry_t entry, unsigned char usage)
 {
         unsigned long offset = swp_offset(entry);
-        unsigned short count;
-        unsigned short has_cache;
+        unsigned char count;
+        unsigned char has_cache;
 
         count = p->swap_map[offset];
         has_cache = count & SWAP_HAS_CACHE;
@@ -591,7 +591,7 @@ void swap_free(swp_entry_t entry)
 void swapcache_free(swp_entry_t entry, struct page *page)
 {
         struct swap_info_struct *p;
-        unsigned short count;
+        unsigned char count;
 
         p = swap_info_get(entry);
         if (p) {
@@ -975,7 +975,7 @@ static unsigned int find_next_to_unuse(struct swap_info_struct *si,
 {
         unsigned int max = si->max;
         unsigned int i = prev;
-        int count;
+        unsigned char count;
 
         /*
          * No need for swap_lock here: we're just looking
@@ -1013,8 +1013,8 @@ static int try_to_unuse(unsigned int type)
 {
         struct swap_info_struct *si = swap_info[type];
         struct mm_struct *start_mm;
-        unsigned short *swap_map;
-        unsigned short swcount;
+        unsigned char *swap_map;
+        unsigned char swcount;
         struct page *page;
         swp_entry_t entry;
         unsigned int i = 0;
@@ -1174,6 +1174,12 @@ static int try_to_unuse(unsigned int type)
                  * If that's wrong, then we should worry more about
                  * exit_mmap() and do_munmap() cases described above:
                  * we might be resetting SWAP_MAP_MAX too early here.
+                 *
+                 * Yes, that's wrong: though very unlikely, swap count 0x7ffe
+                 * could surely occur if pid_max raised from PID_MAX_DEFAULT;
+                 * and we are now lowering SWAP_MAP_MAX to 0x7e, making it
+                 * much easier to reach.  But the next patch will fix that.
+                 *
                  * We know "Undead"s can happen, they're okay, so don't
                  * report them; but do report if we reset SWAP_MAP_MAX.
                  */
@@ -1492,7 +1498,7 @@ bad_bmap:
 SYSCALL_DEFINE1(swapoff, const char __user *, specialfile)
 {
         struct swap_info_struct *p = NULL;
-        unsigned short *swap_map;
+        unsigned char *swap_map;
         struct file *swap_file, *victim;
         struct address_space *mapping;
         struct inode *inode;
@@ -1762,7 +1768,7 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
         sector_t span;
         unsigned long maxpages = 1;
         unsigned long swapfilepages;
-        unsigned short *swap_map = NULL;
+        unsigned char *swap_map = NULL;
         struct page *page = NULL;
         struct inode *inode = NULL;
         int did_down = 0;
@@ -1938,13 +1944,13 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
                 goto bad_swap;
 
         /* OK, set up the swap map and apply the bad block list */
-        swap_map = vmalloc(maxpages * sizeof(short));
+        swap_map = vmalloc(maxpages);
         if (!swap_map) {
                 error = -ENOMEM;
                 goto bad_swap;
         }
 
-        memset(swap_map, 0, maxpages * sizeof(short));
+        memset(swap_map, 0, maxpages);
         for (i = 0; i < swap_header->info.nr_badpages; i++) {
                 int page_nr = swap_header->info.badpages[i];
                 if (page_nr <= 0 || page_nr >= swap_header->info.last_page) {
@@ -2082,12 +2088,12 @@ void si_swapinfo(struct sysinfo *val)
  * - swap-cache reference is requested but there is already one. -> EEXIST
  * - swap-cache reference is requested but the entry is not used. -> ENOENT
  */
-static int __swap_duplicate(swp_entry_t entry, unsigned short usage)
+static int __swap_duplicate(swp_entry_t entry, unsigned char usage)
 {
         struct swap_info_struct *p;
         unsigned long offset, type;
-        unsigned short count;
-        unsigned short has_cache;
+        unsigned char count;
+        unsigned char has_cache;
         int err = -EINVAL;
 
         if (non_swap_entry(entry))