[PATCH] rmap 6 swap_unplug page

From: Hugh Dickins (hugh_at_veritas.com)
Date: 04/11/04

  • Next message: Hugh Dickins: "Re: [PATCH] rmap 6 swap_unplug page" 
    Date:	Sun, 11 Apr 2004 15:26:10 +0100 (BST)
To: Andrew Morton <akpm@osdl.org>

    rmap 6 swap_unplug page

    Good example of "swapper_space considered harmful": swap_unplug_io_fn
    was originally designed for calling via swapper_space.backing_dev_info;
    but that way it loses track of which device is to be unplugged, so had
    to unplug all swap devices. But now sync_page tests SwapCache anyway,
    can call swap_unplug_io_fn with page, which leads direct to the device.

    Reverted -mc4's CONFIG_SWAP=n fix, just add another NOTHING for it.
    Reverted -mc3's editorial adjustments to swap_backing_dev_info and
    swapper_space initializations: they document the few fields which are
    actually used now, as comment above them says (sound of slapped wrist).

     include/linux/swap.h | 5 ++---
     mm/filemap.c | 2 +-
     mm/nommu.c | 5 -----
     mm/swap_state.c | 4 ++--
     mm/swapfile.c | 23 +++++++++++++++--------
     5 files changed, 20 insertions(+), 19 deletions(-)

    --- rmap4/include/linux/swap.h 2004-04-11 07:19:24.105429504 +0100
    +++ rmap5/include/linux/swap.h 2004-04-11 10:38:07.223816856 +0100
    @@ -181,8 +181,6 @@ extern int vm_swappiness;
     extern int shmem_unuse(swp_entry_t entry, struct page *page);
     #endif /* CONFIG_MMU */
     
    -extern void swap_unplug_io_fn(struct backing_dev_info *);
    -
     #ifdef CONFIG_SWAP
     /* linux/mm/page_io.c */
     extern int swap_readpage(struct file *, struct page *);
    @@ -218,7 +216,7 @@ extern sector_t map_swap_page(struct swa
     extern struct swap_info_struct *get_swap_info_struct(unsigned);
     extern int can_share_swap_page(struct page *);
     extern int remove_exclusive_swap_page(struct page *);
    -struct backing_dev_info;
    +extern void swap_unplug_io_fn(struct page *);
     
     extern struct swap_list_t swap_list;
     extern spinlock_t swaplock;
    @@ -252,6 +250,7 @@ extern spinlock_t swaplock;
     #define move_from_swap_cache(p, i, m) 1
     #define __delete_from_swap_cache(p) /*NOTHING*/
     #define delete_from_swap_cache(p) /*NOTHING*/
    +#define swap_unplug_io_fn(p) /*NOTHING*/
     
     static inline int remove_exclusive_swap_page(struct page *p)
     {
    --- rmap4/mm/filemap.c 2004-04-11 07:19:24.796324472 +0100
    +++ rmap5/mm/filemap.c 2004-04-11 10:38:07.226816400 +0100
    @@ -127,7 +127,7 @@ static inline int sync_page(struct page
                     if (mapping->a_ops && mapping->a_ops->sync_page)
                             return mapping->a_ops->sync_page(page);
             } else if (PageSwapCache(page)) {
    - swap_unplug_io_fn(NULL);
    + swap_unplug_io_fn(page);
             }
             return 0;
     }
    --- rmap4/mm/nommu.c 2004-04-11 07:19:24.866313832 +0100
    +++ rmap5/mm/nommu.c 2004-04-11 10:38:07.227816248 +0100
    @@ -18,7 +18,6 @@
     #include <linux/slab.h>
     #include <linux/vmalloc.h>
     #include <linux/blkdev.h>
    -#include <linux/backing-dev.h>
     
     #include <asm/pgalloc.h>
     #include <asm/uaccess.h>
    @@ -572,7 +571,3 @@ unsigned long get_unmapped_area(struct f
     void pte_chain_init(void)
     {
     }
    -
    -void swap_unplug_io_fn(struct backing_dev_info *)
    -{
    -}
    --- rmap4/mm/swap_state.c 2004-04-11 07:19:25.004292856 +0100
    +++ rmap5/mm/swap_state.c 2004-04-11 10:38:07.228816096 +0100
    @@ -25,13 +25,13 @@ static struct address_space_operations s
     };
     
     static struct backing_dev_info swap_backing_dev_info = {
    - .memory_backed = 1, /* Does not contribute to dirty memory */
    - .unplug_io_fn = swap_unplug_io_fn,
    + .state = 0, /* uncongested */
     };
     
     struct address_space swapper_space = {
             .page_tree = RADIX_TREE_INIT(GFP_ATOMIC),
             .tree_lock = SPIN_LOCK_UNLOCKED,
    + .nrpages = 0, /* total_swapcache_pages */
             .a_ops = &swap_aops,
             .backing_dev_info = &swap_backing_dev_info,
     };
    --- rmap4/mm/swapfile.c 2004-04-11 07:19:24.975297264 +0100
    +++ rmap5/mm/swapfile.c 2004-04-11 10:38:07.231815640 +0100
    @@ -86,19 +86,26 @@ static void remove_swap_bdev(struct bloc
             BUG();
     }
     
    -void swap_unplug_io_fn(struct backing_dev_info *unused_bdi)
    +/*
    + * Unlike a standard unplug_io_fn, swap_unplug_io_fn is never called
    + * through swap's backing_dev_info (which is only used by shrink_list),
    + * but directly from sync_page when PageSwapCache: and takes the page
    + * as argument, so that it can find the right device from swp_entry_t.
    + */
    +void swap_unplug_io_fn(struct page *page)
     {
    - int i;
    + swp_entry_t entry;
     
             down(&swap_bdevs_sem);
    - for (i = 0; i < MAX_SWAPFILES; i++) {
    - struct block_device *bdev = swap_bdevs[i];
    + entry.val = page->private;
    + if (PageSwapCache(page)) {
    + struct block_device *bdev = swap_bdevs[swp_type(entry)];
                     struct backing_dev_info *bdi;
     
    - if (bdev == NULL)
    - break;
    - bdi = bdev->bd_inode->i_mapping->backing_dev_info;
    - (*bdi->unplug_io_fn)(bdi);
    + if (bdev) {
    + bdi = bdev->bd_inode->i_mapping->backing_dev_info;
    + (*bdi->unplug_io_fn)(bdi);
    + }
             }
             up(&swap_bdevs_sem);
     }

    -
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