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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: Hugh Dickins <hugh@veritas.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Hugh Dickins 2009-01-06 14:39:50 -08:00 committed by Linus Torvalds
parent 81e3397127
commit ebebbbe904
2 changed files with 42 additions and 34 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

8
include/linux/swap.h
View File

@ -133,14 +133,14 @@ 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 short *swap_map;
unsigned int lowest_bit;
unsigned int highest_bit;
unsigned int cluster_next;
@ -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 {

68
mm/swapfile.c
View File

@ -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)) {
si->cluster_nr = SWAPFILE_CLUSTER - 1;
if (si->pages - si->inuse_pages < SWAPFILE_CLUSTER)
goto lowest;
offset = si->cluster_next;
if (unlikely(!si->cluster_nr--)) {
if (si->pages - si->inuse_pages < SWAPFILE_CLUSTER) {
si->cluster_nr = SWAPFILE_CLUSTER - 1;
goto checks;
}
spin_unlock(&swap_lock);
offset = si->lowest_bit;
@ -118,43 +122,47 @@ 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->lowest_bit)
si->lowest_bit++;
if (offset == si->highest_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->cluster_next = offset + 1;
si->flags -= SWP_SCANNING;
return 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)
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->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;