[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>

diff --git a/include/linux/swap.h b/include/linux/swap.h
index 38f288475e676df44275b6944954e54136611362..f2b16ac0b539da82ee1b5e704197dd9331a6c43e 100644 (file)
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -123,7 +123,6 @@ struct swap_info_struct {
        struct file *swap_file;
        struct block_device *bdev;
        struct list_head extent_list;
-       int nr_extents;
        struct swap_extent *curr_swap_extent;
        unsigned old_block_size;
        unsigned short * swap_map;

diff --git a/mm/swapfile.c b/mm/swapfile.c
index 73521d39e9850f93fc1248651cd9ca66fae827b0..d4da84ee3925b51f859d29beced46a04506a1a6e 100644 (file)
--- 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;