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/*

 *  linux/mm/swap_state.c

 *

 *  Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds

 *  Swap reorganised 29.12.95, Stephen Tweedie

 *

 *  Rewritten to use page cache, (C) 1998 Stephen Tweedie

 */

#include <linux/mm.h>

#include <linux/kernel_stat.h>

#include <linux/swap.h>

#include <linux/swapctl.h>

#include <linux/init.h>

#include <linux/pagemap.h>

#include <linux/smp_lock.h>

#include <asm/pgtable.h>

/*

 * We may have stale swap cache pages in memory: notice

 * them here and get rid of the unnecessary final write.

 */

static int swap_writepage(struct page *page)

{

        if (remove_exclusive_swap_page(page)) {

                UnlockPage(page);

                return 0;

        }

        rw_swap_page(WRITE, page);

        return 0;

}

static struct address_space_operations swap_aops = {

        writepage: swap_writepage,

        sync_page: block_sync_page,

};

struct address_space swapper_space = {

        LIST_HEAD_INIT(swapper_space.clean_pages),

        LIST_HEAD_INIT(swapper_space.dirty_pages),

        LIST_HEAD_INIT(swapper_space.locked_pages),

        0,                               /* nrpages      */

        &swap_aops,

};

#ifdef SWAP_CACHE_INFO

#define INC_CACHE_INFO(x)       (swap_cache_info.x++)

static struct {

        unsigned long add_total;

        unsigned long del_total;

        unsigned long find_success;

        unsigned long find_total;

        unsigned long noent_race;

        unsigned long exist_race;

} swap_cache_info;

void show_swap_cache_info(void)

{

        printk("Swap cache: add %lu, delete %lu, find %lu/%lu, race %lu+%lu\n",

                swap_cache_info.add_total, swap_cache_info.del_total,

                swap_cache_info.find_success, swap_cache_info.find_total,

                swap_cache_info.noent_race, swap_cache_info.exist_race);

}

#else

#define INC_CACHE_INFO(x)       do { } while (0)

#endif

int add_to_swap_cache(struct page *page, swp_entry_t entry)

{

        if (page->mapping)

                BUG();

        if (!swap_duplicate(entry)) {

                INC_CACHE_INFO(noent_race);

                return -ENOENT;

        }

        if (add_to_page_cache_unique(page, &swapper_space, entry.val,

                        page_hash(&swapper_space, entry.val)) != 0) {

                swap_free(entry);

                INC_CACHE_INFO(exist_race);

                return -EEXIST;

        }

        if (!PageLocked(page))

                BUG();

        if (!PageSwapCache(page))

                BUG();

        INC_CACHE_INFO(add_total);

        return 0;

}

/*

 * This must be called only on pages that have

 * been verified to be in the swap cache.

 */

void __delete_from_swap_cache(struct page *page)

{

        if (!PageLocked(page))

                BUG();

        if (!PageSwapCache(page))

                BUG();

        ClearPageDirty(page);

        __remove_inode_page(page);

        INC_CACHE_INFO(del_total);

}

/*

 * This must be called only on pages that have

 * been verified to be in the swap cache and locked.

 * It will never put the page into the free list,

 * the caller has a reference on the page.

 */

void delete_from_swap_cache(struct page *page)

{

        swp_entry_t entry;

        if (!PageLocked(page))

                BUG();

        if (unlikely(!block_flushpage(page, 0)))

                BUG();  /* an anonymous page cannot have page->buffers set */

        entry.val = page->index;

        spin_lock(&pagecache_lock);

        __delete_from_swap_cache(page);

        spin_unlock(&pagecache_lock);

        swap_free(entry);

        page_cache_release(page);

}

/*

 * Perform a free_page(), also freeing any swap cache associated with

 * this page if it is the last user of the page. Can not do a lock_page,

 * as we are holding the page_table_lock spinlock.

 */

void free_page_and_swap_cache(struct page *page)

{

        /*

         * If we are the only user, then try to free up the swap cache.

         *

         * Its ok to check for PageSwapCache without the page lock

         * here because we are going to recheck again inside

         * exclusive_swap_page() _with_ the lock.

         *                                      - Marcelo

         */

        if (PageSwapCache(page) && !TryLockPage(page)) {

                remove_exclusive_swap_page(page);

                UnlockPage(page);

        }

        page_cache_release(page);

}

/*

 * Lookup a swap entry in the swap cache. A found page will be returned

 * unlocked and with its refcount incremented - we rely on the kernel

 * lock getting page table operations atomic even if we drop the page

 * lock before returning.

 */

struct page * lookup_swap_cache(swp_entry_t entry)

{

        struct page *found;

        found = find_get_page(&swapper_space, entry.val);

        /*

         * Unsafe to assert PageSwapCache and mapping on page found:

         * if SMP nothing prevents swapoff from deleting this page from

         * the swap cache at this moment.  find_lock_page would prevent

         * that, but no need to change: we _have_ got the right page.

         */

        INC_CACHE_INFO(find_total);

        if (found)

                INC_CACHE_INFO(find_success);

        return found;

}

/*

 * Locate a page of swap in physical memory, reserving swap cache space

 * and reading the disk if it is not already cached.

 * A failure return means that either the page allocation failed or that

 * the swap entry is no longer in use.

 */

struct page * read_swap_cache_async(swp_entry_t entry)

{

        struct page *found_page, *new_page = NULL;

        int err;

        do {

                /*

                 * First check the swap cache.  Since this is normally

                 * called after lookup_swap_cache() failed, re-calling

                 * that would confuse statistics: use find_get_page()

                 * directly.

                 */

                found_page = find_get_page(&swapper_space, entry.val);

                if (found_page)

                        break;

                /*

                 * Get a new page to read into from swap.

                 */

                if (!new_page) {

                        new_page = alloc_page(GFP_HIGHUSER);

                        if (!new_page)

                                break;          /* Out of memory */

                }

                /*

                 * Associate the page with swap entry in the swap cache.

                 * May fail (-ENOENT) if swap entry has been freed since

                 * our caller observed it.  May fail (-EEXIST) if there

                 * is already a page associated with this entry in the

                 * swap cache: added by a racing read_swap_cache_async,

                 * or by try_to_swap_out (or shmem_writepage) re-using

                 * the just freed swap entry for an existing page.

                 */

                err = add_to_swap_cache(new_page, entry);

                if (!err) {

                        /*

                         * Initiate read into locked page and return.

                         */

                        rw_swap_page(READ, new_page);

                        return new_page;

                }

        } while (err != -ENOENT);

        if (new_page)

                page_cache_release(new_page);

        return found_page;

}