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Commit ebebbbe9 authored by Hugh Dickins's avatar Hugh Dickins Committed by Linus Torvalds
Browse files

swapfile: rearrange scan and swap_info 



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: default avatarHugh Dickins <hugh@veritas.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 81e33971

include/linux/swap.h

+4 −4
Original line number Diff line number Diff line
@@ -133,13 +133,13 @@ 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 int lowest_bit;

	unsigned int highest_bit;
@@ -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 {

mm/swapfile.c

+37 −29
Original line number Diff line number Diff line
@@ -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)) {

	offset = si->cluster_next;



	if (unlikely(!si->cluster_nr--)) {

		if (si->pages - si->inuse_pages < SWAPFILE_CLUSTER) {

			si->cluster_nr = SWAPFILE_CLUSTER - 1;

		if (si->pages - si->inuse_pages < SWAPFILE_CLUSTER)

			goto lowest;

			goto checks;

		}

		spin_unlock(&swap_lock);



		offset = si->lowest_bit;
@@ -118,28 +122,32 @@ 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->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)
@@ -153,8 +161,8 @@ checks: if (!(si->flags & SWP_WRITEOK)) 
	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;