/*
 *  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/module.h>
#include <linux/mm.h>
#include <linux/kernel_stat.h>
#include <linux/swap.h>
#include <linux/init.h>
#include <linux/pagemap.h>
#include <linux/buffer_head.h>
#include <linux/backing-dev.h>
#include <linux/pagevec.h>
#include <linux/migrate.h>

#include <asm/pgtable.h>

/*
 * swapper_space is a fiction, retained to simplify the path through
 * vmscan's shrink_list, to make sync_page look nicer, and to allow
 * future use of radix_tree tags in the swap cache.
 */
static const struct address_space_operations swap_aops = {
        .writepage      = swap_writepage,
        .sync_page      = block_sync_page,
        .set_page_dirty = __set_page_dirty_nobuffers,
        .migratepage    = migrate_page,
};

static struct backing_dev_info swap_backing_dev_info = {
        .capabilities   = BDI_CAP_NO_ACCT_DIRTY | BDI_CAP_NO_WRITEBACK,
        .unplug_io_fn   = swap_unplug_io_fn,
};

struct address_space swapper_space = {
        .page_tree      = RADIX_TREE_INIT(GFP_ATOMIC|__GFP_NOWARN),
        .tree_lock      = __RW_LOCK_UNLOCKED(swapper_space.tree_lock),
        .a_ops          = &swap_aops,
        .i_mmap_nonlinear = LIST_HEAD_INIT(swapper_space.i_mmap_nonlinear),
        .backing_dev_info = &swap_backing_dev_info,
};

#define INC_CACHE_INFO(x)       do { swap_cache_info.x++; } while (0)

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);
        printk("Free swap  = %lukB\n", nr_swap_pages << (PAGE_SHIFT - 10));
        printk("Total swap = %lukB\n", total_swap_pages << (PAGE_SHIFT - 10));
}

/*
 * __add_to_swap_cache resembles add_to_page_cache on swapper_space,
 * but sets SwapCache flag and private instead of mapping and index.
 */
static int __add_to_swap_cache(struct page *page, swp_entry_t entry,
                               gfp_t gfp_mask)
{
        int error;

        BUG_ON(PageSwapCache(page));
        BUG_ON(PagePrivate(page));
        error = radix_tree_preload(gfp_mask);
        if (!error) {
                write_lock_irq(&swapper_space.tree_lock);
                error = radix_tree_insert(&swapper_space.page_tree,
                                                entry.val, page);
                if (!error) {
                        page_cache_get(page);
                        SetPageLocked(page);
                        SetPageSwapCache(page);
                        set_page_private(page, entry.val);
                        total_swapcache_pages++;
                        __inc_zone_page_state(page, NR_FILE_PAGES);
                }
                write_unlock_irq(&swapper_space.tree_lock);
                radix_tree_preload_end();
        }
        return error;
}

static int add_to_swap_cache(struct page *page, swp_entry_t entry)
{
        int error;

        if (!swap_duplicate(entry)) {
                INC_CACHE_INFO(noent_race);
                return -ENOENT;
        }
        error = __add_to_swap_cache(page, entry, GFP_KERNEL);
        /*
         * Anon pages are already on the LRU, we don't run lru_cache_add here.
         */
        if (error) {
                swap_free(entry);
                if (error == -EEXIST)
                        INC_CACHE_INFO(exist_race);
                return error;
        }
        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)
{
        BUG_ON(!PageLocked(page));
        BUG_ON(!PageSwapCache(page));
        BUG_ON(PageWriteback(page));
        BUG_ON(PagePrivate(page));

        radix_tree_delete(&swapper_space.page_tree, page_private(page));
        set_page_private(page, 0);
        ClearPageSwapCache(page);
        total_swapcache_pages--;
        __dec_zone_page_state(page, NR_FILE_PAGES);
        INC_CACHE_INFO(del_total);
}

/**
 * add_to_swap - allocate swap space for a page
 * @page: page we want to move to swap
 *
 * Allocate swap space for the page and add the page to the
 * swap cache.  Caller needs to hold the page lock. 
 */
int add_to_swap(struct page * page, gfp_t gfp_mask)
{
        swp_entry_t entry;
        int err;

        BUG_ON(!PageLocked(page));

        for (;;) {
                entry = get_swap_page();
                if (!entry.val)
                        return 0;

                /*
                 * Radix-tree node allocations from PF_MEMALLOC contexts could
                 * completely exhaust the page allocator. __GFP_NOMEMALLOC
                 * stops emergency reserves from being allocated.
                 *
                 * TODO: this could cause a theoretical memory reclaim
                 * deadlock in the swap out path.
                 */
                /*
                 * Add it to the swap cache and mark it dirty
                 */
                err = __add_to_swap_cache(page, entry,
                                gfp_mask|__GFP_NOMEMALLOC|__GFP_NOWARN);

                switch (err) {
                case 0:                         /* Success */
                        SetPageUptodate(page);
                        SetPageDirty(page);
                        INC_CACHE_INFO(add_total);
                        return 1;
                case -EEXIST:
                        /* Raced with "speculative" read_swap_cache_async */
                        INC_CACHE_INFO(exist_race);
                        swap_free(entry);
                        continue;
                default:
                        /* -ENOMEM radix-tree allocation failure */
                        swap_free(entry);
                        return 0;
                }
        }
}

/*
 * 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;

        entry.val = page_private(page);

        write_lock_irq(&swapper_space.tree_lock);
        __delete_from_swap_cache(page);
        write_unlock_irq(&swapper_space.tree_lock);

        swap_free(entry);
        page_cache_release(page);
}

/*
 * Strange swizzling function only for use by shmem_writepage
 */
int move_to_swap_cache(struct page *page, swp_entry_t entry)
{
        int err = __add_to_swap_cache(page, entry, GFP_ATOMIC);
        if (!err) {
                remove_from_page_cache(page);
                page_cache_release(page);       /* pagecache ref */
                if (!swap_duplicate(entry))
                        BUG();
                SetPageDirty(page);
                INC_CACHE_INFO(add_total);
        } else if (err == -EEXIST)
                INC_CACHE_INFO(exist_race);
        return err;
}

/*
 * Strange swizzling function for shmem_getpage (and shmem_unuse)
 */
int move_from_swap_cache(struct page *page, unsigned long index,
                struct address_space *mapping)
{
        int err = add_to_page_cache(page, mapping, index, GFP_ATOMIC);
        if (!err) {
                delete_from_swap_cache(page);
                /* shift page from clean_pages to dirty_pages list */
                ClearPageDirty(page);
                set_page_dirty(page);
        }
        return err;
}

/* 
 * 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
 */
static inline void free_swap_cache(struct page *page)
{
        if (PageSwapCache(page) && !TestSetPageLocked(page)) {
                remove_exclusive_swap_page(page);
                unlock_page(page);
        }
}

/* 
 * Perform a free_page(), also freeing any swap cache associated with
 * this page if it is the last user of the page.
 */
void free_page_and_swap_cache(struct page *page)
{
        free_swap_cache(page);
        page_cache_release(page);
}

/*
 * Passed an array of pages, drop them all from swapcache and then release
 * them.  They are removed from the LRU and freed if this is their last use.
 */
void free_pages_and_swap_cache(struct page **pages, int nr)
{
        struct page **pagep = pages;

        lru_add_drain();
        while (nr) {
                int todo = min(nr, PAGEVEC_SIZE);
                int i;

                for (i = 0; i < todo; i++)
                        free_swap_cache(pagep[i]);
                release_pages(pagep, todo, 0);
                pagep += todo;
                nr -= todo;
        }
}

/*
 * 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 *page;

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

        if (page)
                INC_CACHE_INFO(find_success);

        INC_CACHE_INFO(find_total);
        return page;
}

/* 
 * 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 vm_area_struct *vma, unsigned long addr)
{
        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.
                 */
                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_vma(GFP_HIGHUSER, vma, addr);
                        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.
                 * May fail (-ENOMEM) if radix-tree node allocation failed.
                 */
                err = add_to_swap_cache(new_page, entry);
                if (!err) {
                        /*
                         * Initiate read into locked page and return.
                         */
                        lru_cache_add_active(new_page);
                        swap_readpage(NULL, new_page);
                        return new_page;
                }
        } while (err != -ENOENT && err != -ENOMEM);

        if (new_page)
                page_cache_release(new_page);
        return found_page;
}