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Date: Thu, 15 Oct 2009 11:37:36 +0900
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To: Hugh Dickins <hugh.dickins@...cali.co.uk>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH 5/9] swap_info: SWAP_HAS_CACHE cleanups
On Thu, 15 Oct 2009 01:52:27 +0100 (BST)
Hugh Dickins <hugh.dickins@...cali.co.uk> wrote:
> 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@...cali.co.uk>
I have no objectios to above.
I'll test, later. maybe no troubles.
Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> ---
>
> 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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