[PATCH] swap: scan_swap_map restyled
Rewrite scan_swap_map to allocate in just the same way as before (taking the
next free entry SWAPFILE_CLUSTER-1 times, then restarting at the lowest wholly
empty cluster, falling back to lowest entry if none), but with a view towards
dropping the lock in the next patch.
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/mm/swapfile.c b/mm/swapfile.c
index e54d60a..c70248a 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -86,64 +86,67 @@
static inline unsigned long scan_swap_map(struct swap_info_struct *si)
{
- unsigned long offset;
- /*
- * We try to cluster swap pages by allocating them
- * sequentially in swap. Once we've allocated
- * SWAPFILE_CLUSTER pages this way, however, we resort to
- * first-free allocation, starting a new cluster. This
- * prevents us from scattering swap pages all over the entire
- * swap partition, so that we reduce overall disk seek times
- * between swap pages. -- sct */
- if (si->cluster_nr) {
- while (si->cluster_next <= si->highest_bit) {
- offset = si->cluster_next++;
- if (si->swap_map[offset])
- continue;
- si->cluster_nr--;
- goto got_page;
- }
- }
- si->cluster_nr = SWAPFILE_CLUSTER;
+ unsigned long offset, last_in_cluster;
- /* try to find an empty (even not aligned) cluster. */
- offset = si->lowest_bit;
- check_next_cluster:
- if (offset+SWAPFILE_CLUSTER-1 <= si->highest_bit)
- {
- unsigned long nr;
- for (nr = offset; nr < offset+SWAPFILE_CLUSTER; nr++)
- if (si->swap_map[nr])
- {
- offset = nr+1;
- goto check_next_cluster;
+ /*
+ * We try to cluster swap pages by allocating them sequentially
+ * in swap. Once we've allocated SWAPFILE_CLUSTER pages this
+ * way, however, we resort to first-free allocation, starting
+ * a new cluster. This prevents us from scattering swap pages
+ * all over the entire swap partition, so that we reduce
+ * overall disk seek times between swap pages. -- sct
+ * But we do now try to find an empty cluster. -Andrea
+ */
+
+ if (unlikely(!si->cluster_nr)) {
+ si->cluster_nr = SWAPFILE_CLUSTER - 1;
+ if (si->pages - si->inuse_pages < SWAPFILE_CLUSTER)
+ goto lowest;
+
+ offset = si->lowest_bit;
+ last_in_cluster = offset + SWAPFILE_CLUSTER - 1;
+
+ /* Locate the first empty (unaligned) cluster */
+ for (; last_in_cluster <= si->highest_bit; offset++) {
+ if (si->swap_map[offset])
+ last_in_cluster = offset + SWAPFILE_CLUSTER;
+ else if (offset == last_in_cluster) {
+ si->cluster_next = offset-SWAPFILE_CLUSTER-1;
+ goto cluster;
}
- /* We found a completly empty cluster, so start
- * using it.
- */
- goto got_page;
+ }
+ goto lowest;
}
- /* No luck, so now go finegrined as usual. -Andrea */
- for (offset = si->lowest_bit; offset <= si->highest_bit ; offset++) {
- if (si->swap_map[offset])
- continue;
- si->lowest_bit = offset+1;
- got_page:
- if (offset == si->lowest_bit)
+
+ si->cluster_nr--;
+cluster:
+ offset = si->cluster_next;
+ if (offset > si->highest_bit)
+lowest: offset = si->lowest_bit;
+ if (!si->highest_bit)
+ goto no_page;
+ if (!si->swap_map[offset]) {
+got_page: if (offset == si->lowest_bit)
si->lowest_bit++;
if (offset == si->highest_bit)
si->highest_bit--;
- if (si->lowest_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->inuse_pages++;
- si->cluster_next = offset+1;
+ si->cluster_next = offset + 1;
return offset;
}
- si->lowest_bit = si->max;
- si->highest_bit = 0;
+
+ while (++offset <= si->highest_bit) {
+ if (!si->swap_map[offset])
+ goto got_page;
+ }
+ goto lowest;
+
+no_page:
return 0;
}