Commit 253d553b authored by Hugh Dickins's avatar Hugh Dickins Committed by Linus Torvalds
Browse files

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: default avatarHugh Dickins <hugh.dickins@tiscali.co.uk>
Reviewed-by: default avatarKAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Rik van Riel <riel@redhat.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 73c34b6a

include/linux/swap.h

+1 −1
Original line number Diff line number Diff line
@@ -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.

 */

mm/swapfile.c

+64 −91
Original line number Diff line number Diff line
@@ -53,30 +53,9 @@ static struct swap_info_struct *swap_info[MAX_SWAPFILES]; 


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 type) 
	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_info_struct *p, 
		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 entry) 


	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);
@@ -1212,7 +1183,7 @@ static int try_to_unuse(unsigned int type) 


		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;

		}
@@ -2111,16 +2082,16 @@ 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)
@@ -2129,54 +2100,56 @@ static int __swap_duplicate(swp_entry_t entry, bool cache) 
	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);

}



/*
@@ -2189,7 +2162,7 @@ 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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