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>
diff --git a/mm/compaction.c b/mm/compaction.c
index 8be430b..dcb058b 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -42,8 +42,6 @@
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 @@
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 @@
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 @@
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 @@
.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 @@
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 @@
.nr_freepages = 0,
.nr_migratepages = 0,
.order = -1,
- .compact_mode = COMPACT_MODE_DIRECT_RECLAIM,
};
zone = &pgdat->node_zones[zoneid];