From: Hugh Dickins <hugh@veritas.com>
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).
---
25-akpm/include/linux/swap.h | 5 ++---
25-akpm/mm/filemap.c | 2 +-
25-akpm/mm/nommu.c | 5 -----
25-akpm/mm/swap_state.c | 4 ++--
25-akpm/mm/swapfile.c | 23 +++++++++++++++--------
5 files changed, 20 insertions(+), 19 deletions(-)
diff -puN include/linux/swap.h~rmap-5-swap_unplug-page include/linux/swap.h
--- 25/include/linux/swap.h~rmap-5-swap_unplug-page 2004-04-11 12:39:03.598313048 -0700
+++ 25-akpm/include/linux/swap.h 2004-04-11 12:39:03.608311528 -0700
@@ -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)
{
diff -puN mm/filemap.c~rmap-5-swap_unplug-page mm/filemap.c
--- 25/mm/filemap.c~rmap-5-swap_unplug-page 2004-04-11 12:39:03.600312744 -0700
+++ 25-akpm/mm/filemap.c 2004-04-11 12:39:03.609311376 -0700
@@ -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;
}
diff -puN mm/nommu.c~rmap-5-swap_unplug-page mm/nommu.c
--- 25/mm/nommu.c~rmap-5-swap_unplug-page 2004-04-11 12:39:03.601312592 -0700
+++ 25-akpm/mm/nommu.c 2004-04-11 12:39:03.610311224 -0700
@@ -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 *)
-{
-}
diff -puN mm/swapfile.c~rmap-5-swap_unplug-page mm/swapfile.c
--- 25/mm/swapfile.c~rmap-5-swap_unplug-page 2004-04-11 12:39:03.603312288 -0700
+++ 25-akpm/mm/swapfile.c 2004-04-11 12:39:03.612310920 -0700
@@ -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);
}
diff -puN mm/swap_state.c~rmap-5-swap_unplug-page mm/swap_state.c
--- 25/mm/swap_state.c~rmap-5-swap_unplug-page 2004-04-11 12:39:03.605311984 -0700
+++ 25-akpm/mm/swap_state.c 2004-04-11 12:39:03.611311072 -0700
@@ -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,
};
_