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vmscan: stop kswapd waiting on congestion when the min watermark is not being met 

If reclaim fails to make sufficient progress, the priority is raised.
Once the priority is higher, kswapd starts waiting on congestion.
However, if the zone is below the min watermark then kswapd needs to
continue working without delay as there is a danger of an increased rate
of GFP_ATOMIC allocation failure.

This patch changes the conditions under which kswapd waits on congestion
by only going to sleep if the min watermarks are being met.

[mel@csn.ul.ie: add stats to track how relevant the logic is]
[mel@csn.ul.ie: make kswapd only check its own zones and rename the relevant counters]
Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Signed-off-by: Mel Gorman <mel@csn.ul.ie>
Reviewed-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
KOSAKI Motohiro 2009-12-14 17:58:55 -08:00 committed by Linus Torvalds
parent f50de2d381
commit bb3ab59683
3 changed files with 34 additions and 12 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

3
include/linux/vmstat.h
View File

@ -40,7 +40,8 @@ enum vm_event_item { PGPGIN, PGPGOUT, PSWPIN, PSWPOUT,
PGSCAN_ZONE_RECLAIM_FAILED,
#endif
PGINODESTEAL, SLABS_SCANNED, KSWAPD_STEAL, KSWAPD_INODESTEAL,
KSWAPD_PREMATURE_FAST, KSWAPD_PREMATURE_SLOW,
KSWAPD_LOW_WMARK_HIT_QUICKLY, KSWAPD_HIGH_WMARK_HIT_QUICKLY,
KSWAPD_SKIP_CONGESTION_WAIT,
PAGEOUTRUN, ALLOCSTALL, PGROTATED,
#ifdef CONFIG_HUGETLB_PAGE
HTLB_BUDDY_PGALLOC, HTLB_BUDDY_PGALLOC_FAIL,

38
mm/vmscan.c
View File

@ -1905,19 +1905,25 @@ unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *mem_cont,
#endif
/* is kswapd sleeping prematurely? */
static int sleeping_prematurely(int order, long remaining)
static int sleeping_prematurely(pg_data_t *pgdat, int order, long remaining)
{
struct zone *zone;
int i;
/* If a direct reclaimer woke kswapd within HZ/10, it's premature */
if (remaining)
return 1;
/* If after HZ/10, a zone is below the high mark, it's premature */
for_each_populated_zone(zone)
for (i = 0; i < pgdat->nr_zones; i++) {
struct zone *zone = pgdat->node_zones + i;
if (!populated_zone(zone))
continue;
if (!zone_watermark_ok(zone, order, high_wmark_pages(zone),
0, 0))
return 1;
}
return 0;
}
@ -1979,6 +1985,7 @@ loop_again:
for (priority = DEF_PRIORITY; priority >= 0; priority--) {
int end_zone = 0; /* Inclusive. 0 = ZONE_DMA */
unsigned long lru_pages = 0;
int has_under_min_watermark_zone = 0;
/* The swap token gets in the way of swapout... */
if (!priority)
@ -2085,6 +2092,15 @@ loop_again:
if (total_scanned > SWAP_CLUSTER_MAX * 2 &&
total_scanned > sc.nr_reclaimed + sc.nr_reclaimed / 2)
sc.may_writepage = 1;
/*
* We are still under min water mark. it mean we have
* GFP_ATOMIC allocation failure risk. Hurry up!
*/
if (!zone_watermark_ok(zone, order, min_wmark_pages(zone),
end_zone, 0))
has_under_min_watermark_zone = 1;
}
if (all_zones_ok)
break; /* kswapd: all done */
@ -2092,8 +2108,12 @@ loop_again:
* OK, kswapd is getting into trouble. Take a nap, then take
* another pass across the zones.
*/
if (total_scanned && priority < DEF_PRIORITY - 2)
congestion_wait(BLK_RW_ASYNC, HZ/10);
if (total_scanned && (priority < DEF_PRIORITY - 2)) {
if (has_under_min_watermark_zone)
count_vm_event(KSWAPD_SKIP_CONGESTION_WAIT);
else
congestion_wait(BLK_RW_ASYNC, HZ/10);
}
/*
* We do this so kswapd doesn't build up large priorities for
@ -2207,7 +2227,7 @@ static int kswapd(void *p)
long remaining = 0;
/* Try to sleep for a short interval */
if (!sleeping_prematurely(order, remaining)) {
if (!sleeping_prematurely(pgdat, order, remaining)) {
remaining = schedule_timeout(HZ/10);
finish_wait(&pgdat->kswapd_wait, &wait);
prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);
@ -2218,13 +2238,13 @@ static int kswapd(void *p)
* premature sleep. If not, then go fully
* to sleep until explicitly woken up
*/
if (!sleeping_prematurely(order, remaining))
if (!sleeping_prematurely(pgdat, order, remaining))
schedule();
else {
if (remaining)
count_vm_event(KSWAPD_PREMATURE_FAST);
count_vm_event(KSWAPD_LOW_WMARK_HIT_QUICKLY);
else
count_vm_event(KSWAPD_PREMATURE_SLOW);
count_vm_event(KSWAPD_HIGH_WMARK_HIT_QUICKLY);
}
}

5
mm/vmstat.c
View File

@ -683,8 +683,9 @@ static const char * const vmstat_text[] = {
"slabs_scanned",
"kswapd_steal",
"kswapd_inodesteal",
"kswapd_slept_prematurely_fast",
"kswapd_slept_prematurely_slow",
"kswapd_low_wmark_hit_quickly",
"kswapd_high_wmark_hit_quickly",
"kswapd_skip_congestion_wait",
"pageoutrun",
"allocstall",