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mm: compaction: prevent kswapd compacting memory to reduce CPU usage

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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.

[[email protected]: Beefed up the changelog]
Signed-off-by: Andrea Arcangeli <[email protected]>
Signed-off-by: Mel Gorman <[email protected]>
Reported-by: Arthur Marsh <[email protected]>
Tested-by: Arthur Marsh <[email protected]>
Cc: <[email protected]>		[2.6.38.1]
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
This commit is contained in:
Andrea Arcangeli 2011-03-22 16:30:38 -07:00 • committed by Linus Torvalds
commit d527caf22e
3 changed files with 6 additions and 45 deletions
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24
mm/compaction.c
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@ -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];