[PATCH] swap: swap extent list is ordered
There are several comments that swap's extent_list.prev points to the lowest
extent: that's not so, it's extent_list.next which points to it, as you'd
expect. And a couple of loops in add_swap_extent which go all the way through
the list, when they should just add to the other end.
Fix those up, and let map_swap_page search the list forwards: profiles shows
it to be twice as quick that way - because prefetch works better on how the
structs are typically kmalloc'ed? or because usually more is written to than
read from swap, and swap is allocated ascendingly?
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 4b39e95..73521d3 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -832,9 +832,9 @@
offset < (se->start_page + se->nr_pages)) {
return se->start_block + (offset - se->start_page);
}
- lh = se->list.prev;
+ lh = se->list.next;
if (lh == &sis->extent_list)
- lh = lh->prev;
+ 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 */
@@ -859,10 +859,9 @@
/*
* Add a block range (and the corresponding page range) into this swapdev's
- * extent list. The extent list is kept sorted in block order.
+ * extent list. The extent list is kept sorted in page order.
*
- * This function rather assumes that it is called in ascending sector_t order.
- * It doesn't look for extent coalescing opportunities.
+ * This function rather assumes that it is called in ascending page order.
*/
static int
add_swap_extent(struct swap_info_struct *sis, unsigned long start_page,
@@ -872,16 +871,15 @@
struct swap_extent *new_se;
struct list_head *lh;
- lh = sis->extent_list.next; /* The highest-addressed block */
- while (lh != &sis->extent_list) {
+ lh = sis->extent_list.prev; /* The highest page extent */
+ if (lh != &sis->extent_list) {
se = list_entry(lh, struct swap_extent, list);
- if (se->start_block + se->nr_pages == start_block &&
- se->start_page + se->nr_pages == start_page) {
+ BUG_ON(se->start_page + se->nr_pages != start_page);
+ if (se->start_block + se->nr_pages == start_block) {
/* Merge it */
se->nr_pages += nr_pages;
return 0;
}
- lh = lh->next;
}
/*
@@ -894,14 +892,7 @@
new_se->nr_pages = nr_pages;
new_se->start_block = start_block;
- lh = sis->extent_list.prev; /* The lowest block */
- while (lh != &sis->extent_list) {
- se = list_entry(lh, struct swap_extent, list);
- if (se->start_block > start_block)
- break;
- lh = lh->prev;
- }
- list_add_tail(&new_se->list, lh);
+ list_add_tail(&new_se->list, &sis->extent_list);
sis->nr_extents++;
return 0;
}