swapfile: rearrange scan and swap_info
Hugh Dickins [Tue, 6 Jan 2009 22:39:50 +0000 (14:39 -0800)]
Before making functional changes, rearrange scan_swap_map() to simplify
subsequent diffs.  Actually, there is one functional change in there:
leave cluster_nr negative while scanning for a new cluster - resetting it
early increased the likelihood that when we have difficulty finding a free
cluster, another task may come in and try doing exactly the same - just a
waste of cpu.

Before making functional changes, rearrange struct swap_info_struct
slightly: flags will be needed as an unsigned long (for wait_on_bit), next
is a good int to pair with prio, old_block_size is uninteresting so shift
it to the end.

Signed-off-by: Hugh Dickins <hugh@veritas.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/swap.h
mm/swapfile.c

index 410c8e4..9cabb8b 100644 (file)
@@ -133,14 +133,14 @@ enum {
  * The in-memory structure used to track swap areas.
  */
 struct swap_info_struct {
-       unsigned int flags;
+       unsigned long flags;
        int prio;                       /* swap priority */
+       int next;                       /* next entry on swap list */
        struct file *swap_file;
        struct block_device *bdev;
        struct list_head extent_list;
        struct swap_extent *curr_swap_extent;
-       unsigned old_block_size;
-       unsigned short * swap_map;
+       unsigned short *swap_map;
        unsigned int lowest_bit;
        unsigned int highest_bit;
        unsigned int cluster_next;
@@ -148,7 +148,7 @@ struct swap_info_struct {
        unsigned int pages;
        unsigned int max;
        unsigned int inuse_pages;
-       int next;                       /* next entry on swap list */
+       unsigned int old_block_size;
 };
 
 struct swap_list_t {
index 85ff603..4d9855f 100644 (file)
@@ -89,7 +89,8 @@ void swap_unplug_io_fn(struct backing_dev_info *unused_bdi, struct page *page)
 
 static inline unsigned long scan_swap_map(struct swap_info_struct *si)
 {
-       unsigned long offset, last_in_cluster;
+       unsigned long offset;
+       unsigned long last_in_cluster;
        int latency_ration = LATENCY_LIMIT;
 
        /*
@@ -103,10 +104,13 @@ static inline unsigned long scan_swap_map(struct swap_info_struct *si)
         */
 
        si->flags += SWP_SCANNING;
-       if (unlikely(!si->cluster_nr)) {
-               si->cluster_nr = SWAPFILE_CLUSTER - 1;
-               if (si->pages - si->inuse_pages < SWAPFILE_CLUSTER)
-                       goto lowest;
+       offset = si->cluster_next;
+
+       if (unlikely(!si->cluster_nr--)) {
+               if (si->pages - si->inuse_pages < SWAPFILE_CLUSTER) {
+                       si->cluster_nr = SWAPFILE_CLUSTER - 1;
+                       goto checks;
+               }
                spin_unlock(&swap_lock);
 
                offset = si->lowest_bit;
@@ -118,43 +122,47 @@ static inline unsigned long scan_swap_map(struct swap_info_struct *si)
                                last_in_cluster = offset + SWAPFILE_CLUSTER;
                        else if (offset == last_in_cluster) {
                                spin_lock(&swap_lock);
-                               si->cluster_next = offset-SWAPFILE_CLUSTER+1;
-                               goto cluster;
+                               offset -= SWAPFILE_CLUSTER - 1;
+                               si->cluster_next = offset;
+                               si->cluster_nr = SWAPFILE_CLUSTER - 1;
+                               goto checks;
                        }
                        if (unlikely(--latency_ration < 0)) {
                                cond_resched();
                                latency_ration = LATENCY_LIMIT;
                        }
                }
+
+               offset = si->lowest_bit;
                spin_lock(&swap_lock);
-               goto lowest;
+               si->cluster_nr = SWAPFILE_CLUSTER - 1;
        }
 
-       si->cluster_nr--;
-cluster:
-       offset = si->cluster_next;
-       if (offset > si->highest_bit)
-lowest:                offset = si->lowest_bit;
-checks:        if (!(si->flags & SWP_WRITEOK))
+checks:
+       if (!(si->flags & SWP_WRITEOK))
                goto no_page;
        if (!si->highest_bit)
                goto no_page;
-       if (!si->swap_map[offset]) {
-               if (offset == si->lowest_bit)
-                       si->lowest_bit++;
-               if (offset == si->highest_bit)
-                       si->highest_bit--;
-               si->inuse_pages++;
-               if (si->inuse_pages == si->pages) {
-                       si->lowest_bit = si->max;
-                       si->highest_bit = 0;
-               }
-               si->swap_map[offset] = 1;
-               si->cluster_next = offset + 1;
-               si->flags -= SWP_SCANNING;
-               return offset;
+       if (offset > si->highest_bit)
+               offset = si->lowest_bit;
+       if (si->swap_map[offset])
+               goto scan;
+
+       if (offset == si->lowest_bit)
+               si->lowest_bit++;
+       if (offset == si->highest_bit)
+               si->highest_bit--;
+       si->inuse_pages++;
+       if (si->inuse_pages == si->pages) {
+               si->lowest_bit = si->max;
+               si->highest_bit = 0;
        }
+       si->swap_map[offset] = 1;
+       si->cluster_next = offset + 1;
+       si->flags -= SWP_SCANNING;
+       return offset;
 
+scan:
        spin_unlock(&swap_lock);
        while (++offset <= si->highest_bit) {
                if (!si->swap_map[offset]) {
@@ -167,7 +175,7 @@ checks:     if (!(si->flags & SWP_WRITEOK))
                }
        }
        spin_lock(&swap_lock);
-       goto lowest;
+       goto checks;
 
 no_page:
        si->flags -= SWP_SCANNING;