[PATCH] swap: show span of swap extents

The "Adding %dk swap" message shows the number of swap extents, as a guide to
how fragmented the swapfile may be.  But a useful further guide is what total
extent they span across (sometimes scarily large).

And there's no need to keep nr_extents in swap_info: it's unused after the
initial message, so save a little space by keeping it on stack.

Signed-off-by: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 30 insertions, 14 deletions

diff --git a/mm/swapfile.c b/mm/swapfile.c
index 73521d39e985..d4da84ee3925 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -854,7 +854,6 @@ static void destroy_swap_extents(struct swap_info_struct *sis)
                 list_del(&se->list);
                 kfree(se);
         }
-        sis->nr_extents = 0;
 }
 
 /*
@@ -893,8 +892,7 @@ add_swap_extent(struct swap_info_struct *sis, unsigned long start_page,
         new_se->start_block = start_block;
 
         list_add_tail(&new_se->list, &sis->extent_list);
-        sis->nr_extents++;
-        return 0;
+        return 1;
 }
 
 /*
@@ -928,7 +926,7 @@ add_swap_extent(struct swap_info_struct *sis, unsigned long start_page,
  * This is extremely effective.  The average number of iterations in
  * map_swap_page() has been measured at about 0.3 per page.  - akpm.
  */
-static int setup_swap_extents(struct swap_info_struct *sis)
+static int setup_swap_extents(struct swap_info_struct *sis, sector_t *span)
 {
         struct inode *inode;
         unsigned blocks_per_page;
@@ -936,11 +934,15 @@ static int setup_swap_extents(struct swap_info_struct *sis)
         unsigned blkbits;
         sector_t probe_block;
         sector_t last_block;
+        sector_t lowest_block = -1;
+        sector_t highest_block = 0;
+        int nr_extents = 0;
         int ret;
 
         inode = sis->swap_file->f_mapping->host;
         if (S_ISBLK(inode->i_mode)) {
                 ret = add_swap_extent(sis, 0, sis->max, 0);
+                *span = sis->pages;
                 goto done;
         }
 
@@ -985,19 +987,28 @@ static int setup_swap_extents(struct swap_info_struct *sis)
                         }
                 }
 
+                first_block >>= (PAGE_SHIFT - blkbits);
+                if (page_no) {  /* exclude the header page */
+                        if (first_block < lowest_block)
+                                lowest_block = first_block;
+                        if (first_block > highest_block)
+                                highest_block = first_block;
+                }
+
                 /*
                  * We found a PAGE_SIZE-length, PAGE_SIZE-aligned run of blocks
                  */
-                ret = add_swap_extent(sis, page_no, 1,
-                                first_block >> (PAGE_SHIFT - blkbits));
-                if (ret)
+                ret = add_swap_extent(sis, page_no, 1, first_block);
+                if (ret < 0)
                         goto out;
+                nr_extents += ret;
                 page_no++;
                 probe_block += blocks_per_page;
 reprobe:
                 continue;
         }
-        ret = 0;
+        ret = nr_extents;
+        *span = 1 + highest_block - lowest_block;
         if (page_no == 0)
                 page_no = 1;    /* force Empty message */
         sis->max = page_no;
@@ -1265,6 +1276,8 @@ asmlinkage long sys_swapon(const char __user * specialfile, int swap_flags)
         union swap_header *swap_header = NULL;
         int swap_header_version;
         int nr_good_pages = 0;
+        int nr_extents;
+        sector_t span;
         unsigned long maxpages = 1;
         int swapfilesize;
         unsigned short *swap_map;
@@ -1300,7 +1313,6 @@ asmlinkage long sys_swapon(const char __user * specialfile, int swap_flags)
                 nr_swapfiles = type+1;
         INIT_LIST_HEAD(&p->extent_list);
         p->flags = SWP_USED;
-        p->nr_extents = 0;
         p->swap_file = NULL;
         p->old_block_size = 0;
         p->swap_map = NULL;
@@ -1477,9 +1489,11 @@ asmlinkage long sys_swapon(const char __user * specialfile, int swap_flags)
                 p->swap_map[0] = SWAP_MAP_BAD;
                 p->max = maxpages;
                 p->pages = nr_good_pages;
-                error = setup_swap_extents(p);
-                if (error)
+                nr_extents = setup_swap_extents(p, &span);
+                if (nr_extents < 0) {
+                        error = nr_extents;
                         goto bad_swap;
+                }
                 nr_good_pages = p->pages;
         }
         if (!nr_good_pages) {
@@ -1494,9 +1508,11 @@ asmlinkage long sys_swapon(const char __user * specialfile, int swap_flags)
         p->flags = SWP_ACTIVE;
         nr_swap_pages += nr_good_pages;
         total_swap_pages += nr_good_pages;
-        printk(KERN_INFO "Adding %dk swap on %s.  Priority:%d extents:%d\n",
-                nr_good_pages<<(PAGE_SHIFT-10), name,
-                p->prio, p->nr_extents);
+
+        printk(KERN_INFO "Adding %dk swap on %s.  "
+                        "Priority:%d extents:%d across:%lluk\n",
+                nr_good_pages<<(PAGE_SHIFT-10), name, p->prio,
+                nr_extents, (unsigned long long)span<<(PAGE_SHIFT-10));
 
         /* insert swap space into swap_list: */
         prev = -1;