FreeBSD/Linux Kernel Cross Reference
sys/mm/swap_state.c

     /*
      *  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;
   }

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