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Subject[PATCH 6/9] 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>
---

include/linux/swap.h | 8 ++++----
mm/swapfile.c | 40 +++++++++++++++++++++++-----------------
2 files changed, 27 insertions(+), 21 deletions(-)

--- si5/include/linux/swap.h 2009-10-14 21:26:42.000000000 +0100
+++ si6/include/linux/swap.h 2009-10-14 21:26:49.000000000 +0100
@@ -151,9 +151,9 @@ enum {

#define SWAP_CLUSTER_MAX 32

-#define SWAP_MAP_MAX 0x7ffe
-#define SWAP_MAP_BAD 0x7fff
-#define SWAP_HAS_CACHE 0x8000 /* There is a swap cache of entry. */
+#define SWAP_MAP_MAX 0x7e
+#define SWAP_MAP_BAD 0x7f
+#define SWAP_HAS_CACHE 0x80 /* There is a swap cache of entry. */

/*
* The in-memory structure used to track swap areas.
@@ -167,7 +167,7 @@ struct swap_info_struct {
struct block_device *bdev;
struct swap_extent first_swap_extent;
struct swap_extent *curr_swap_extent;
- unsigned short *swap_map;
+ unsigned char *swap_map;
unsigned int lowest_bit;
unsigned int highest_bit;
unsigned int lowest_alloc; /* while preparing discard cluster */
--- si5/mm/swapfile.c 2009-10-14 21:26:42.000000000 +0100
+++ si6/mm/swapfile.c 2009-10-14 21:26:49.000000000 +0100
@@ -53,7 +53,7 @@ static struct swap_info_struct *swap_inf

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(s
{
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 typ
{
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;
@@ -1175,6 +1175,12 @@ static int try_to_unuse(unsigned int typ
* 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.
*/
@@ -1494,7 +1500,7 @@ 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;
@@ -1764,7 +1770,7 @@ SYSCALL_DEFINE2(swapon, const char __use
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;
@@ -1939,13 +1945,13 @@ SYSCALL_DEFINE2(swapon, const char __use
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) {
@@ -2083,12 +2089,12 @@ 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))

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