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Commit 11d31886 authored by Hugh Dickins's avatar Hugh Dickins Committed by Linus Torvalds
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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: default avatarHugh Dickins <hugh@veritas.com>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent 4cd3bb10

include/linux/swap.h

+0 −2
Original line number Diff line number Diff line
@@ -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;

mm/swapfile.c

+9 −18
Original line number Diff line number Diff line
@@ -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;

}