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[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>
This commit is contained in:
Hugh Dickins 2005-09-03 15:54:34 -07:00 committed by Linus Torvalds
parent 4cd3bb10ff
commit 11d31886db
2 changed files with 9 additions and 20 deletions
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2
include/linux/swap.h
View File

@ -116,8 +116,6 @@ enum {
/*
* The in-memory structure used to track swap areas.
* extent_list.prev points at the lowest-index extent. That list is
* sorted.
*/
struct swap_info_struct {
unsigned int flags;

27
mm/swapfile.c
View File

@ -832,9 +832,9 @@ sector_t map_swap_page(struct swap_info_struct *sis, pgoff_t offset)
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 @@ static void destroy_swap_extents(struct swap_info_struct *sis)
/*
* 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 @@ add_swap_extent(struct swap_info_struct *sis, unsigned long start_page,
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 @@ add_swap_extent(struct swap_info_struct *sis, unsigned long start_page,
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;
}