/*
 *  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/init.h>
#include <linux/pagemap.h>
#include <linux/backing-dev.h>
#include <linux/buffer_head.h>  /* block_sync_page() */

#include <asm/pgtable.h>

/*
 * swapper_inode doesn't do anything much.  It is really only here to
 * avoid some special-casing in other parts of the kernel.
 */
static struct inode swapper_inode = {
        .i_mapping      = &swapper_space,
};

static struct backing_dev_info swap_backing_dev_info = {
        .ra_pages       = 0,    /* No readahead */
        .memory_backed  = 1,    /* Does not contribute to dirty memory */
};

extern struct address_space_operations swap_aops;

struct address_space swapper_space = {
        .page_tree              = RADIX_TREE_INIT(GFP_ATOMIC),
        .page_lock              = RW_LOCK_UNLOCKED,
        .clean_pages            = LIST_HEAD_INIT(swapper_space.clean_pages),
        .dirty_pages            = LIST_HEAD_INIT(swapper_space.dirty_pages),
        .io_pages               = LIST_HEAD_INIT(swapper_space.io_pages),
        .locked_pages           = LIST_HEAD_INIT(swapper_space.locked_pages),
        .host                   = &swapper_inode,
        .a_ops                  = &swap_aops,
        .backing_dev_info       = &swap_backing_dev_info,
        .i_shared_lock          = SPIN_LOCK_UNLOCKED,
        .private_lock           = SPIN_LOCK_UNLOCKED,
        .private_list           = LIST_HEAD_INIT(swapper_space.private_list),
};

#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);
}

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

        if (page->mapping)
                BUG();
        if (!swap_duplicate(entry)) {
                INC_CACHE_INFO(noent_race);
                return -ENOENT;
        }
        error = add_to_page_cache(page, &swapper_space, entry.val);
        /*
         * Anon pages are already on the LRU, we don't run lru_cache_add here.
         */
        if (error != 0) {
                swap_free(entry);
                if (error == -EEXIST)
                        INC_CACHE_INFO(exist_race);
                return error;
        }
        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)
{
        BUG_ON(!PageLocked(page));
        BUG_ON(!PageSwapCache(page));
        BUG_ON(PageWriteback(page));
        ClearPageDirty(page);
        __remove_from_page_cache(page);
        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)
{
        swp_entry_t entry;
        int pf_flags;

        if (!PageLocked(page))
                BUG();

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

                /* Radix-tree node allocations are performing
                 * GFP_ATOMIC allocations under PF_MEMALLOC.  
                 * They can completely exhaust the page allocator.  
                 *
                 * So PF_MEMALLOC is dropped here.  This causes the slab 
                 * allocations to fail earlier, so radix-tree nodes will 
                 * then be allocated from the mempool reserves.
                 *
                 * We're still using __GFP_HIGH for radix-tree node
                 * allocations, so some of the emergency pools are available,
                 * just not all of them.
                 */

                pf_flags = current->flags;
                current->flags &= ~PF_MEMALLOC;
                current->flags |= PF_NOWARN;
                ClearPageUptodate(page);                /* why? */

                /*
                 * Add it to the swap cache and mark it dirty
                 * (adding to the page cache will clear the dirty
                 * and uptodate bits, so we need to do it again)
                 */
                switch (add_to_swap_cache(page, entry)) {
                case 0:                         /* Success */
                        current->flags = pf_flags;
                        SetPageUptodate(page);
                        set_page_dirty(page);
                        swap_free(entry);
                        return 1;
                case -ENOMEM:                   /* radix-tree allocation */
                        current->flags = pf_flags;
                        swap_free(entry);
                        return 0;
                default:                        /* ENOENT: raced */
                        break;
                }
                /* Raced with "speculative" read_swap_cache_async */
                current->flags = pf_flags;
                swap_free(entry);
        }
}

/*
 * 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;

        BUG_ON(!PageLocked(page));
        BUG_ON(PageWriteback(page));
        BUG_ON(page_has_buffers(page));
  
        entry.val = page->index;

        write_lock(&swapper_space.page_lock);
        __delete_from_swap_cache(page);
        write_unlock(&swapper_space.page_lock);

        swap_free(entry);
        page_cache_release(page);
}

int move_to_swap_cache(struct page *page, swp_entry_t entry)
{
        struct address_space *mapping = page->mapping;
        void **pslot;
        int err;

        if (!mapping)
                BUG();

        if (!swap_duplicate(entry)) {
                INC_CACHE_INFO(noent_race);
                return -ENOENT;
        }

        write_lock(&swapper_space.page_lock);
        write_lock(&mapping->page_lock);

        err = radix_tree_reserve(&swapper_space.page_tree, entry.val, &pslot);
        if (!err) {
                /* Remove it from the page cache */
                __remove_from_page_cache(page);

                /* Add it to the swap cache */
                *pslot = page;
                /*
                 * This code used to clear PG_uptodate, PG_error, PG_arch1,
                 * PG_referenced and PG_checked.  What _should_ it clear?
                 */
                ClearPageUptodate(page);
                ClearPageReferenced(page);

                SetPageLocked(page);
                ClearPageDirty(page);
                ___add_to_page_cache(page, &swapper_space, entry.val);
        }

        write_unlock(&mapping->page_lock);
        write_unlock(&swapper_space.page_lock);

        if (!err) {
                INC_CACHE_INFO(add_total);
                return 0;
        }

        swap_free(entry);

        if (err == -EEXIST)
                INC_CACHE_INFO(exist_race);

        return err;
}

int move_from_swap_cache(struct page *page, unsigned long index,
                struct address_space *mapping)
{
        void **pslot;
        int err;

        BUG_ON(!PageLocked(page));
        BUG_ON(PageWriteback(page));
        BUG_ON(page_has_buffers(page));

        write_lock(&swapper_space.page_lock);
        write_lock(&mapping->page_lock);

        err = radix_tree_reserve(&mapping->page_tree, index, &pslot);
        if (!err) {
                swp_entry_t entry;

                entry.val = page->index;
                __delete_from_swap_cache(page);

                *pslot = page;

                /*
                 * This code used to clear PG_uptodate, PG_error, PG_referenced,
                 * PG_arch_1 and PG_checked.  It's not really clear why.
                 */
                ClearPageUptodate(page);
                ClearPageReferenced(page);

                /*
                 * ___add_to_page_cache puts the page on ->clean_pages,
                 * but it's dirty.  If it's on ->clean_pages, it will basically
                 * never get written out.
                 */
                SetPageDirty(page);
                ___add_to_page_cache(page, mapping, index);
                /* fix that up */
                list_move(&page->list, &mapping->dirty_pages);
                write_unlock(&mapping->page_lock);
                write_unlock(&swapper_space.page_lock);

                /* Do this outside ->page_lock */
                swap_free(entry);
                return 0;
        }

        write_unlock(&mapping->page_lock);
        write_unlock(&swapper_space.page_lock);
        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. Can not do a lock_page,
 * as we are holding the page_table_lock spinlock.
 */
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)
{
        const int chunk = 16;
        struct page **pagep = pages;

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

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