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Subject[PATCH 5/9] swap_info: SWAP_HAS_CACHE cleanups
Though swap_count() is useful, I'm finding that swap_has_cache() and
encode_swapmap() obscure what happens in the swap_map entry, just at
those points where I need to understand it. Remove them, and pass
more usable "usage" values to scan_swap_map(), swap_entry_free() and
__swap_duplicate(), instead of the SWAP_MAP and SWAP_CACHE enum.

Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
---

include/linux/swap.h | 2
mm/swapfile.c | 155 ++++++++++++++++-------------------------
2 files changed, 65 insertions(+), 92 deletions(-)

--- si4/include/linux/swap.h 2009-10-14 21:26:22.000000000 +0100
+++ si5/include/linux/swap.h 2009-10-14 21:26:42.000000000 +0100
@@ -154,7 +154,7 @@ enum {
#define SWAP_MAP_MAX 0x7ffe
#define SWAP_MAP_BAD 0x7fff
#define SWAP_HAS_CACHE 0x8000 /* There is a swap cache of entry. */
-#define SWAP_COUNT_MASK (~SWAP_HAS_CACHE)
+
/*
* The in-memory structure used to track swap areas.
*/
--- si4/mm/swapfile.c 2009-10-14 21:26:32.000000000 +0100
+++ si5/mm/swapfile.c 2009-10-14 21:26:42.000000000 +0100
@@ -53,30 +53,9 @@ static struct swap_info_struct *swap_inf

static DEFINE_MUTEX(swapon_mutex);

-/* For reference count accounting in swap_map */
-/* enum for swap_map[] handling. internal use only */
-enum {
- SWAP_MAP = 0, /* ops for reference from swap users */
- SWAP_CACHE, /* ops for reference from swap cache */
-};
-
static inline int swap_count(unsigned short ent)
{
- return ent & SWAP_COUNT_MASK;
-}
-
-static inline bool swap_has_cache(unsigned short ent)
-{
- return !!(ent & SWAP_HAS_CACHE);
-}
-
-static inline unsigned short encode_swapmap(int count, bool has_cache)
-{
- unsigned short ret = count;
-
- if (has_cache)
- return SWAP_HAS_CACHE | ret;
- return ret;
+ return ent & ~SWAP_HAS_CACHE;
}

/* returns 1 if swap entry is freed */
@@ -224,7 +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,
- int cache)
+ unsigned short usage)
{
unsigned long offset;
unsigned long scan_base;
@@ -355,10 +334,7 @@ checks:
si->lowest_bit = si->max;
si->highest_bit = 0;
}
- if (cache == SWAP_CACHE) /* at usual swap-out via vmscan.c */
- si->swap_map[offset] = encode_swapmap(0, true);
- else /* at suspend */
- si->swap_map[offset] = encode_swapmap(1, false);
+ si->swap_map[offset] = usage;
si->cluster_next = offset + 1;
si->flags -= SWP_SCANNING;

@@ -483,7 +459,7 @@ swp_entry_t get_swap_page(void)

swap_list.next = next;
/* This is called for allocating swap entry for cache */
- offset = scan_swap_map(si, SWAP_CACHE);
+ offset = scan_swap_map(si, SWAP_HAS_CACHE);
if (offset) {
spin_unlock(&swap_lock);
return swp_entry(type, offset);
@@ -508,7 +484,7 @@ swp_entry_t get_swap_page_of_type(int ty
if (si && (si->flags & SWP_WRITEOK)) {
nr_swap_pages--;
/* This is called for allocating swap entry, not cache */
- offset = scan_swap_map(si, SWAP_MAP);
+ offset = scan_swap_map(si, 1);
if (offset) {
spin_unlock(&swap_lock);
return swp_entry(type, offset);
@@ -555,29 +531,31 @@ out:
return NULL;
}

-static int swap_entry_free(struct swap_info_struct *p,
- swp_entry_t ent, int cache)
+static unsigned short swap_entry_free(struct swap_info_struct *p,
+ swp_entry_t entry, unsigned short usage)
{
- unsigned long offset = swp_offset(ent);
- int count = swap_count(p->swap_map[offset]);
- bool has_cache;
+ unsigned long offset = swp_offset(entry);
+ unsigned short count;
+ unsigned short has_cache;

- has_cache = swap_has_cache(p->swap_map[offset]);
+ count = p->swap_map[offset];
+ has_cache = count & SWAP_HAS_CACHE;
+ count &= ~SWAP_HAS_CACHE;

- if (cache == SWAP_MAP) { /* dropping usage count of swap */
- if (count < SWAP_MAP_MAX) {
- count--;
- p->swap_map[offset] = encode_swapmap(count, has_cache);
- }
- } else { /* dropping swap cache flag */
+ if (usage == SWAP_HAS_CACHE) {
VM_BUG_ON(!has_cache);
- p->swap_map[offset] = encode_swapmap(count, false);
+ has_cache = 0;
+ } else if (count < SWAP_MAP_MAX)
+ count--;
+
+ if (!count)
+ mem_cgroup_uncharge_swap(entry);
+
+ usage = count | has_cache;
+ p->swap_map[offset] = usage;

- }
- /* return code. */
- count = p->swap_map[offset];
/* free if no reference */
- if (!count) {
+ if (!usage) {
if (offset < p->lowest_bit)
p->lowest_bit = offset;
if (offset > p->highest_bit)
@@ -588,9 +566,8 @@ static int swap_entry_free(struct swap_i
nr_swap_pages++;
p->inuse_pages--;
}
- if (!swap_count(count))
- mem_cgroup_uncharge_swap(ent);
- return count;
+
+ return usage;
}

/*
@@ -603,7 +580,7 @@ void swap_free(swp_entry_t entry)

p = swap_info_get(entry);
if (p) {
- swap_entry_free(p, entry, SWAP_MAP);
+ swap_entry_free(p, entry, 1);
spin_unlock(&swap_lock);
}
}
@@ -614,19 +591,13 @@ void swap_free(swp_entry_t entry)
void swapcache_free(swp_entry_t entry, struct page *page)
{
struct swap_info_struct *p;
- int ret;
+ unsigned short count;

p = swap_info_get(entry);
if (p) {
- ret = swap_entry_free(p, entry, SWAP_CACHE);
- if (page) {
- bool swapout;
- if (ret)
- swapout = true; /* the end of swap out */
- else
- swapout = false; /* no more swap users! */
- mem_cgroup_uncharge_swapcache(page, entry, swapout);
- }
+ count = swap_entry_free(p, entry, SWAP_HAS_CACHE);
+ if (page)
+ mem_cgroup_uncharge_swapcache(page, entry, count != 0);
spin_unlock(&swap_lock);
}
}
@@ -705,7 +676,7 @@ int free_swap_and_cache(swp_entry_t entr

p = swap_info_get(entry);
if (p) {
- if (swap_entry_free(p, entry, SWAP_MAP) == SWAP_HAS_CACHE) {
+ if (swap_entry_free(p, entry, 1) == SWAP_HAS_CACHE) {
page = find_get_page(&swapper_space, entry.val);
if (page && !trylock_page(page)) {
page_cache_release(page);
@@ -1213,7 +1184,7 @@ static int try_to_unuse(unsigned int typ

if (swap_count(*swap_map) == SWAP_MAP_MAX) {
spin_lock(&swap_lock);
- *swap_map = encode_swapmap(0, true);
+ *swap_map = SWAP_HAS_CACHE;
spin_unlock(&swap_lock);
reset_overflow = 1;
}
@@ -2112,16 +2083,16 @@ 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, bool cache)
+static int __swap_duplicate(swp_entry_t entry, unsigned short usage)
{
struct swap_info_struct *p;
unsigned long offset, type;
- int result = -EINVAL;
- int count;
- bool has_cache;
+ unsigned short count;
+ unsigned short has_cache;
+ int err = -EINVAL;

if (non_swap_entry(entry))
- return -EINVAL;
+ goto out;

type = swp_type(entry);
if (type >= nr_swapfiles)
@@ -2130,54 +2101,56 @@ static int __swap_duplicate(swp_entry_t
offset = swp_offset(entry);

spin_lock(&swap_lock);
-
if (unlikely(offset >= p->max))
goto unlock_out;

- count = swap_count(p->swap_map[offset]);
- has_cache = swap_has_cache(p->swap_map[offset]);
+ count = p->swap_map[offset];
+ has_cache = count & SWAP_HAS_CACHE;
+ count &= ~SWAP_HAS_CACHE;
+ err = 0;

- if (cache == SWAP_CACHE) { /* called for swapcache/swapin-readahead */
+ if (usage == SWAP_HAS_CACHE) {

/* set SWAP_HAS_CACHE if there is no cache and entry is used */
- if (!has_cache && count) {
- p->swap_map[offset] = encode_swapmap(count, true);
- result = 0;
- } else if (has_cache) /* someone added cache */
- result = -EEXIST;
- else if (!count) /* no users */
- result = -ENOENT;
+ if (!has_cache && count)
+ has_cache = SWAP_HAS_CACHE;
+ else if (has_cache) /* someone else added cache */
+ err = -EEXIST;
+ else /* no users remaining */
+ err = -ENOENT;

} else if (count || has_cache) {
- if (count < SWAP_MAP_MAX - 1) {
- p->swap_map[offset] = encode_swapmap(count + 1,
- has_cache);
- result = 0;
- } else if (count <= SWAP_MAP_MAX) {
+
+ if (count < SWAP_MAP_MAX - 1)
+ count++;
+ else if (count <= SWAP_MAP_MAX) {
if (swap_overflow++ < 5)
printk(KERN_WARNING
"swap_dup: swap entry overflow\n");
- p->swap_map[offset] = encode_swapmap(SWAP_MAP_MAX,
- has_cache);
- result = 0;
- }
+ count = SWAP_MAP_MAX;
+ } else
+ err = -EINVAL;
} else
- result = -ENOENT; /* unused swap entry */
+ err = -ENOENT; /* unused swap entry */
+
+ p->swap_map[offset] = count | has_cache;
+
unlock_out:
spin_unlock(&swap_lock);
out:
- return result;
+ return err;

bad_file:
printk(KERN_ERR "swap_dup: %s%08lx\n", Bad_file, entry.val);
goto out;
}
+
/*
* increase reference count of swap entry by 1.
*/
void swap_duplicate(swp_entry_t entry)
{
- __swap_duplicate(entry, SWAP_MAP);
+ __swap_duplicate(entry, 1);
}

/*
@@ -2190,7 +2163,7 @@ void swap_duplicate(swp_entry_t entry)
*/
int swapcache_prepare(swp_entry_t entry)
{
- return __swap_duplicate(entry, SWAP_CACHE);
+ return __swap_duplicate(entry, SWAP_HAS_CACHE);
}

/*

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