swap_info: include first_swap_extent

Make better use of the space by folding first swap_extent into its
swap_info_struct, instead of just the list_head: swap partitions need
only that one, and for others it's used as a circular list anyway.

[jirislaby@gmail.com: fix crash on double swapon]
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Rik van Riel <riel@redhat.com>
Signed-off-by: Jiri Slaby <jirislaby@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 36 insertions, 34 deletions

diff --git a/mm/swapfile.c b/mm/swapfile.c
index dc88a7e4257e..16de84b56644 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -145,23 +145,28 @@ void swap_unplug_io_fn(struct backing_dev_info *unused_bdi, struct page *page)
 static int discard_swap(struct swap_info_struct *si)
 {
         struct swap_extent *se;
+        sector_t start_block;
+        sector_t nr_blocks;
         int err = 0;
 
-        list_for_each_entry(se, &si->extent_list, list) {
-                sector_t start_block = se->start_block << (PAGE_SHIFT - 9);
-                sector_t nr_blocks = (sector_t)se->nr_pages << (PAGE_SHIFT - 9);
+        /* Do not discard the swap header page! */
+        se = &si->first_swap_extent;
+        start_block = (se->start_block + 1) << (PAGE_SHIFT - 9);
+        nr_blocks = ((sector_t)se->nr_pages - 1) << (PAGE_SHIFT - 9);
+        if (nr_blocks) {
+                err = blkdev_issue_discard(si->bdev, start_block,
+                                nr_blocks, GFP_KERNEL, DISCARD_FL_BARRIER);
+                if (err)
+                        return err;
+                cond_resched();
+        }
 
-                if (se->start_page == 0) {
-                        /* Do not discard the swap header page! */
-                        start_block += 1 << (PAGE_SHIFT - 9);
-                        nr_blocks -= 1 << (PAGE_SHIFT - 9);
-                        if (!nr_blocks)
-                                continue;
-                }
+        list_for_each_entry(se, &si->first_swap_extent.list, list) {
+                start_block = se->start_block << (PAGE_SHIFT - 9);
+                nr_blocks = (sector_t)se->nr_pages << (PAGE_SHIFT - 9);
 
                 err = blkdev_issue_discard(si->bdev, start_block,
-                                                nr_blocks, GFP_KERNEL,
-                                                DISCARD_FL_BARRIER);
+                                nr_blocks, GFP_KERNEL, DISCARD_FL_BARRIER);
                 if (err)
                         break;
 
@@ -200,14 +205,11 @@ static void discard_swap_cluster(struct swap_info_struct *si,
                         start_block <<= PAGE_SHIFT - 9;
                         nr_blocks <<= PAGE_SHIFT - 9;
                         if (blkdev_issue_discard(si->bdev, start_block,
-                                                        nr_blocks, GFP_NOIO,
-                                                        DISCARD_FL_BARRIER))
+                                    nr_blocks, GFP_NOIO, DISCARD_FL_BARRIER))
                                 break;
                 }
 
                 lh = se->list.next;
-                if (lh == &si->extent_list)
-                        lh = lh->next;
                 se = list_entry(lh, struct swap_extent, list);
         }
 }
@@ -761,10 +763,8 @@ int swap_type_of(dev_t device, sector_t offset, struct block_device **bdev_p)
                         return type;
                 }
                 if (bdev == sis->bdev) {
-                        struct swap_extent *se;
+                        struct swap_extent *se = &sis->first_swap_extent;
 
-                        se = list_entry(sis->extent_list.next,
-                                        struct swap_extent, list);
                         if (se->start_block == offset) {
                                 if (bdev_p)
                                         *bdev_p = bdgrab(sis->bdev);
@@ -1310,8 +1310,6 @@ sector_t map_swap_page(swp_entry_t entry, struct block_device **bdev)
                         return se->start_block + (offset - se->start_page);
                 }
                 lh = se->list.next;
-                if (lh == &sis->extent_list)
-                        lh = lh->next;
                 se = list_entry(lh, struct swap_extent, list);
                 sis->curr_swap_extent = se;
                 BUG_ON(se == start_se);         /* It *must* be present */
@@ -1340,10 +1338,10 @@ sector_t swapdev_block(int type, pgoff_t offset)
  */
 static void destroy_swap_extents(struct swap_info_struct *sis)
 {
-        while (!list_empty(&sis->extent_list)) {
+        while (!list_empty(&sis->first_swap_extent.list)) {
                 struct swap_extent *se;
 
-                se = list_entry(sis->extent_list.next,
+                se = list_entry(sis->first_swap_extent.list.next,
                                 struct swap_extent, list);
                 list_del(&se->list);
                 kfree(se);
@@ -1364,8 +1362,15 @@ add_swap_extent(struct swap_info_struct *sis, unsigned long start_page,
         struct swap_extent *new_se;
         struct list_head *lh;
 
-        lh = sis->extent_list.prev;     /* The highest page extent */
-        if (lh != &sis->extent_list) {
+        if (start_page == 0) {
+                se = &sis->first_swap_extent;
+                sis->curr_swap_extent = se;
+                se->start_page = 0;
+                se->nr_pages = nr_pages;
+                se->start_block = start_block;
+                return 1;
+        } else {
+                lh = sis->first_swap_extent.list.prev;  /* Highest extent */
                 se = list_entry(lh, struct swap_extent, list);
                 BUG_ON(se->start_page + se->nr_pages != start_page);
                 if (se->start_block + se->nr_pages == start_block) {
@@ -1385,7 +1390,7 @@ add_swap_extent(struct swap_info_struct *sis, unsigned long start_page,
         new_se->nr_pages = nr_pages;
         new_se->start_block = start_block;
 
-        list_add_tail(&new_se->list, &sis->extent_list);
+        list_add_tail(&new_se->list, &sis->first_swap_extent.list);
         return 1;
 }
 
@@ -1437,7 +1442,7 @@ static int setup_swap_extents(struct swap_info_struct *sis, sector_t *span)
         if (S_ISBLK(inode->i_mode)) {
                 ret = add_swap_extent(sis, 0, sis->max, 0);
                 *span = sis->pages;
-                goto done;
+                goto out;
         }
 
         blkbits = inode->i_blkbits;
@@ -1508,15 +1513,12 @@ reprobe:
         sis->max = page_no;
         sis->pages = page_no - 1;
         sis->highest_bit = page_no - 1;
-done:
-        sis->curr_swap_extent = list_entry(sis->extent_list.prev,
-                                        struct swap_extent, list);
-        goto out;
+out:
+        return ret;
 bad_bmap:
         printk(KERN_ERR "swapon: swapfile has holes\n");
         ret = -EINVAL;
-out:
-        return ret;
+        goto out;
 }
 
 SYSCALL_DEFINE1(swapoff, const char __user *, specialfile)
@@ -1815,7 +1817,6 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
                 kfree(p);
                 goto out;
         }
-        INIT_LIST_HEAD(&p->extent_list);
         if (type >= nr_swapfiles) {
                 p->type = type;
                 swap_info[type] = p;
@@ -1834,6 +1835,7 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
                  * would be relying on p->type to remain valid.
                  */
         }
+        INIT_LIST_HEAD(&p->first_swap_extent.list);
         p->flags = SWP_USED;
         p->next = -1;
         spin_unlock(&swap_lock);