Commit d527caf2 authored by Andrea Arcangeli's avatar Andrea Arcangeli Committed by Linus Torvalds

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: default avatarAndrea Arcangeli <aarcange@redhat.com>
Signed-off-by: default avatarMel Gorman <mel@csn.ul.ie>
Reported-by: default avatarArthur Marsh <arthur.marsh@internode.on.net>
Tested-by: default avatarArthur Marsh <arthur.marsh@internode.on.net>
Cc: <stable@kernel.org>		[2.6.38.1]
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 89699605
......@@ -11,9 +11,6 @@
/* The full zone was compacted */
#define COMPACT_COMPLETE 3
#define COMPACT_MODE_DIRECT_RECLAIM 0
#define COMPACT_MODE_KSWAPD 1
#ifdef CONFIG_COMPACTION
extern int sysctl_compact_memory;
extern int sysctl_compaction_handler(struct ctl_table *table, int write,
......@@ -28,8 +25,7 @@ extern unsigned long try_to_compact_pages(struct zonelist *zonelist,
bool sync);
extern unsigned long compaction_suitable(struct zone *zone, int order);
extern unsigned long compact_zone_order(struct zone *zone, int order,
gfp_t gfp_mask, bool sync,
int compact_mode);
gfp_t gfp_mask, bool sync);
/* Do not skip compaction more than 64 times */
#define COMPACT_MAX_DEFER_SHIFT 6
......@@ -74,8 +70,7 @@ static inline unsigned long compaction_suitable(struct zone *zone, int order)
}
static inline unsigned long compact_zone_order(struct zone *zone, int order,
gfp_t gfp_mask, bool sync,
int compact_mode)
gfp_t gfp_mask, bool sync)
{
return COMPACT_CONTINUE;
}
......
......@@ -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];
......
......@@ -2397,7 +2397,6 @@ loop_again:
* cause too much scanning of the lower zones.
*/
for (i = 0; i <= end_zone; i++) {
int compaction;
struct zone *zone = pgdat->node_zones + i;
int nr_slab;
......@@ -2428,24 +2427,9 @@ loop_again:
sc.nr_reclaimed += reclaim_state->reclaimed_slab;
total_scanned += sc.nr_scanned;
compaction = 0;
if (order &&
zone_watermark_ok(zone, 0,
high_wmark_pages(zone),
end_zone, 0) &&
!zone_watermark_ok(zone, order,
high_wmark_pages(zone),
end_zone, 0)) {
compact_zone_order(zone,
order,
sc.gfp_mask, false,
COMPACT_MODE_KSWAPD);
compaction = 1;
}
if (zone->all_unreclaimable)
continue;
if (!compaction && nr_slab == 0 &&
if (nr_slab == 0 &&
!zone_reclaimable(zone))
zone->all_unreclaimable = 1;
/*
......
Markdown is supported
0% or
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment