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authorAndrea Arcangeli <aarcange@redhat.com>2011-03-22 16:30:38 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2011-03-22 17:44:00 -0700
commitd527caf22e48480b102c7c6ee5b9ba12170148f7 (patch)
tree7d53a2c430f8c020b6fa8390396dd2d1ce480b9a /mm/compaction.c
parent89699605fe7cfd8611900346f61cb6cbf179b10a (diff)
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mm: compaction: prevent kswapd compacting memory to reduce CPU usage
This patch reverts 5a03b051 ("thp: use compaction in kswapd for GFP_ATOMIC order > 0") due to reports stating that kswapd CPU usage was higher and IRQs were being disabled more frequently. This was reported at http://www.spinics.net/linux/fedora/alsa-user/msg09885.html. Without this patch applied, CPU usage by kswapd hovers around the 20% mark according to the tester (Arthur Marsh: http://www.spinics.net/linux/fedora/alsa-user/msg09899.html). With this patch applied, it's around 2%. The problem is not related to THP which specifies __GFP_NO_KSWAPD but is triggered by high-order allocations hitting the low watermark for their order and waking kswapd on kernels with CONFIG_COMPACTION set. The most common trigger for this is network cards configured for jumbo frames but it's also possible it'll be triggered by fork-heavy workloads (order-1) and some wireless cards which depend on order-1 allocations. The symptoms for the user will be high CPU usage by kswapd in low-memory situations which could be confused with another writeback problem. While a patch like 5a03b051 may be reintroduced in the future, this patch plays it safe for now and reverts it. [mel@csn.ul.ie: Beefed up the changelog] Signed-off-by: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by: Mel Gorman <mel@csn.ul.ie> Reported-by: Arthur Marsh <arthur.marsh@internode.on.net> Tested-by: Arthur Marsh <arthur.marsh@internode.on.net> Cc: <stable@kernel.org> [2.6.38.1] Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/compaction.c')
-rw-r--r--mm/compaction.c24
1 files changed, 3 insertions, 21 deletions
diff --git a/mm/compaction.c b/mm/compaction.c
index 8be430b812de..dcb058bd76c4 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -42,8 +42,6 @@ struct compact_control {
unsigned int order; /* order a direct compactor needs */
int migratetype; /* MOVABLE, RECLAIMABLE etc */
struct zone *zone;
-
- int compact_mode;
};
static unsigned long release_freepages(struct list_head *freelist)
@@ -397,10 +395,7 @@ static int compact_finished(struct zone *zone,
return COMPACT_COMPLETE;
/* Compaction run is not finished if the watermark is not met */
- if (cc->compact_mode != COMPACT_MODE_KSWAPD)
- watermark = low_wmark_pages(zone);
- else
- watermark = high_wmark_pages(zone);
+ watermark = low_wmark_pages(zone);
watermark += (1 << cc->order);
if (!zone_watermark_ok(zone, cc->order, watermark, 0, 0))
@@ -413,15 +408,6 @@ static int compact_finished(struct zone *zone,
if (cc->order == -1)
return COMPACT_CONTINUE;
- /*
- * Generating only one page of the right order is not enough
- * for kswapd, we must continue until we're above the high
- * watermark as a pool for high order GFP_ATOMIC allocations
- * too.
- */
- if (cc->compact_mode == COMPACT_MODE_KSWAPD)
- return COMPACT_CONTINUE;
-
/* Direct compactor: Is a suitable page free? */
for (order = cc->order; order < MAX_ORDER; order++) {
/* Job done if page is free of the right migratetype */
@@ -543,8 +529,7 @@ static int compact_zone(struct zone *zone, struct compact_control *cc)
unsigned long compact_zone_order(struct zone *zone,
int order, gfp_t gfp_mask,
- bool sync,
- int compact_mode)
+ bool sync)
{
struct compact_control cc = {
.nr_freepages = 0,
@@ -553,7 +538,6 @@ unsigned long compact_zone_order(struct zone *zone,
.migratetype = allocflags_to_migratetype(gfp_mask),
.zone = zone,
.sync = sync,
- .compact_mode = compact_mode,
};
INIT_LIST_HEAD(&cc.freepages);
INIT_LIST_HEAD(&cc.migratepages);
@@ -599,8 +583,7 @@ unsigned long try_to_compact_pages(struct zonelist *zonelist,
nodemask) {
int status;
- status = compact_zone_order(zone, order, gfp_mask, sync,
- COMPACT_MODE_DIRECT_RECLAIM);
+ status = compact_zone_order(zone, order, gfp_mask, sync);
rc = max(status, rc);
/* If a normal allocation would succeed, stop compacting */
@@ -631,7 +614,6 @@ static int compact_node(int nid)
.nr_freepages = 0,
.nr_migratepages = 0,
.order = -1,
- .compact_mode = COMPACT_MODE_DIRECT_RECLAIM,
};
zone = &pgdat->node_zones[zoneid];