From: Andrea Arcangeli <andrea@suse.de>
I don't think we need an install_swap_bdev/remove_swap_bdev anymore, we should
use the swap_info->bdev, not the swap_bdevs. the swap_info already has a
->bdev field, the only point of remove_swap_bdev/install_swap_bdev was to
unplug all devices as efficiently as possible, we don't need that anymore with
the page parameter.
Plus the semaphore should be a rwsem to allow parallel unplug from multiple
pages.
After that I don't need to take the semaphore anymore during swapon, no
swapcache with swp_type() pointing to such bdev, will be allowed until swapon
is complete (SWP_ACTIVE is set a lot later after setting p->bdev).
In swapoff I only need a dummy serialization with the readers, after
try_to_unuse is complete:
err = try_to_unuse(type);
current->flags &= ~PF_SWAPOFF;
/* wait for any unplug function to finish */
down_write(&swap_unplug_sem);
up_write(&swap_unplug_sem);
that's all, no other locking and no install_swap_bdev/remove_swap_bdev.
(and the swap_bdevs[] compression code was busted)
---
25-akpm/mm/swapfile.c | 74 ++++++++++++++------------------------------
drivers/block/ll_rw_blk.c | 0
fs/buffer.c | 0
include/linux/backing-dev.h | 0
include/linux/blkdev.h | 0
include/linux/swap.h | 0
mm/readahead.c | 0
7 files changed, 25 insertions(+), 49 deletions(-)
diff -puN drivers/block/ll_rw_blk.c~swap-speedups-and-fix drivers/block/ll_rw_blk.c
diff -puN fs/buffer.c~swap-speedups-and-fix fs/buffer.c
diff -puN include/linux/backing-dev.h~swap-speedups-and-fix include/linux/backing-dev.h
diff -puN include/linux/blkdev.h~swap-speedups-and-fix include/linux/blkdev.h
diff -puN include/linux/swap.h~swap-speedups-and-fix include/linux/swap.h
diff -puN mm/readahead.c~swap-speedups-and-fix mm/readahead.c
diff -puN mm/swapfile.c~swap-speedups-and-fix mm/swapfile.c
--- 25/mm/swapfile.c~swap-speedups-and-fix 2004-05-12 21:01:25.758751368 -0700
+++ 25-akpm/mm/swapfile.c 2004-05-12 21:01:25.762750760 -0700
@@ -48,61 +48,38 @@ struct swap_info_struct swap_info[MAX_SW
static DECLARE_MUTEX(swapon_sem);
/*
- * Array of backing blockdevs, for swap_unplug_fn. We need this because the
- * bdev->unplug_fn can sleep and we cannot hold swap_list_lock while calling
- * the unplug_fn. And swap_list_lock cannot be turned into a semaphore.
+ * We need this because the bdev->unplug_fn can sleep and we cannot
+ * hold swap_list_lock while calling the unplug_fn. And swap_list_lock
+ * cannot be turned into a semaphore.
*/
-static DECLARE_MUTEX(swap_bdevs_sem);
-static struct block_device *swap_bdevs[MAX_SWAPFILES];
+static DECLARE_RWSEM(swap_unplug_sem);
#define SWAPFILE_CLUSTER 256
-/*
- * Caller holds swap_bdevs_sem
- */
-static void install_swap_bdev(struct block_device *bdev)
-{
- int i;
-
- for (i = 0; i < MAX_SWAPFILES; i++) {
- if (swap_bdevs[i] == NULL) {
- swap_bdevs[i] = bdev;
- return;
- }
- }
- BUG();
-}
-
-static void remove_swap_bdev(struct block_device *bdev)
-{
- int i;
-
- for (i = 0; i < MAX_SWAPFILES; i++) {
- if (swap_bdevs[i] == bdev) {
- memcpy(&swap_bdevs[i], &swap_bdevs[i + 1],
- (MAX_SWAPFILES - i - 1) * sizeof(*swap_bdevs));
- swap_bdevs[MAX_SWAPFILES - 1] = NULL;
- return;
- }
- }
- BUG();
-}
-
void swap_unplug_io_fn(struct backing_dev_info *unused_bdi, 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];
+ down_read(&swap_unplug_sem);
+ entry.val = page->private;
+ if (PageSwapCache(page)) {
+ struct block_device *bdev = swap_info[swp_type(entry)].bdev;
struct backing_dev_info *bdi;
- if (bdev == NULL)
- break;
+ /*
+ * If the page is removed from swapcache from under us (with a
+ * racy try_to_unuse/swapoff) we need an additional reference
+ * count to avoid reading garbage from page->private above. If
+ * the WARN_ON triggers during a swapoff it maybe the race
+ * condition and it's harmless. However if it triggers without
+ * swapoff it signals a problem.
+ */
+ WARN_ON(page_count(page) <= 1);
+
bdi = bdev->bd_inode->i_mapping->backing_dev_info;
bdi->unplug_io_fn(bdi, page);
}
- up(&swap_bdevs_sem);
+ up_read(&swap_unplug_sem);
}
static inline int scan_swap_map(struct swap_info_struct *si)
@@ -1136,6 +1113,11 @@ asmlinkage long sys_swapoff(const char _
current->flags |= PF_SWAPOFF;
err = try_to_unuse(type);
current->flags &= ~PF_SWAPOFF;
+
+ /* wait for any unplug function to finish */
+ down_write(&swap_unplug_sem);
+ up_write(&swap_unplug_sem);
+
if (err) {
/* re-insert swap space back into swap_list */
swap_list_lock();
@@ -1154,7 +1136,6 @@ asmlinkage long sys_swapoff(const char _
goto out_dput;
}
down(&swapon_sem);
- down(&swap_bdevs_sem);
swap_list_lock();
swap_device_lock(p);
swap_file = p->swap_file;
@@ -1166,8 +1147,6 @@ asmlinkage long sys_swapoff(const char _
destroy_swap_extents(p);
swap_device_unlock(p);
swap_list_unlock();
- remove_swap_bdev(p->bdev);
- up(&swap_bdevs_sem);
up(&swapon_sem);
vfree(swap_map);
if (S_ISBLK(mapping->host->i_mode)) {
@@ -1511,7 +1490,6 @@ asmlinkage long sys_swapon(const char __
goto bad_swap;
down(&swapon_sem);
- down(&swap_bdevs_sem);
swap_list_lock();
swap_device_lock(p);
p->flags = SWP_ACTIVE;
@@ -1537,8 +1515,6 @@ asmlinkage long sys_swapon(const char __
}
swap_device_unlock(p);
swap_list_unlock();
- install_swap_bdev(p->bdev);
- up(&swap_bdevs_sem);
up(&swapon_sem);
error = 0;
goto out;
_