diff --git a/mm/vmscan.c b/mm/vmscan.c
index a74bf72..a578535 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2261,7 +2261,7 @@ static bool sleeping_prematurely(pg_data_t *pgdat, int order, long remaining,
 		return true;
 
 	/* Check the watermark levels */
-	for (i = 0; i < pgdat->nr_zones; i++) {
+	for (i = 0; i <= classzone_idx; i++) {
 		struct zone *zone = pgdat->node_zones + i;
 
 		if (!populated_zone(zone))
-- 
1.7.0.4


From c774fd4d541e2b930ca21382755d1084f39f5587 Mon Sep 17 00:00:00 2001
From: Mel Gorman <mel@csn.ul.ie>
Date: Tue, 22 Mar 2011 16:33:04 -0700
Subject: [PATCH 2/5] mm: vmscan: kswapd should not free an excessive number of pages when balancing small zones

BugLink: http://bugs.launchpad.net/bugs/808509

When reclaiming for order-0 pages, kswapd requires that all zones be
balanced.  Each cycle through balance_pgdat() does background ageing on
all zones if necessary and applies equal pressure on the inactive zone
unless a lot of pages are free already.

A "lot of free pages" is defined as a "balance gap" above the high
watermark which is currently 7*high_watermark.  Historically this was
reasonable as min_free_kbytes was small.  However, on systems using huge
pages, it is recommended that min_free_kbytes is higher and it is tuned
with hugeadm --set-recommended-min_free_kbytes.  With the introduction of
transparent huge page support, this recommended value is also applied.  On
X86-64 with 4G of memory, min_free_kbytes becomes 67584 so one would
expect around 68M of memory to be free.  The Normal zone is approximately
35000 pages so under even normal memory pressure such as copying a large
file, it gets exhausted quickly.  As it is getting exhausted, kswapd
applies pressure equally to all zones, including the DMA32 zone.  DMA32 is
approximately 700,000 pages with a high watermark of around 23,000 pages.
In this situation, kswapd will reclaim around (23000*8 where 8 is the high
watermark + balance gap of 7 * high watermark) pages or 718M of pages
before the zone is ignored.  What the user sees is that free memory far
higher than it should be.

To avoid an excessive number of pages being reclaimed from the larger
zones, explicitely defines the "balance gap" to be either 1% of the zone
or the low watermark for the zone, whichever is smaller.  While kswapd
will check all zones to apply pressure, it'll ignore zones that meets the
(high_wmark + balance_gap) watermark.

To test this, 80G were copied from a partition and the amount of memory
being used was recorded.  A comparison of a patch and unpatched kernel can
be seen at
http://www.csn.ul.ie/~mel/postings/minfree-20110222/memory-usage-hydra.ps
and shows that kswapd is not reclaiming as much memory with the patch
applied.

Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Mel Gorman <mel@csn.ul.ie>
Acked-by: Rik van Riel <riel@redhat.com>
Cc: Shaohua Li <shaohua.li@intel.com>
Cc: "Chen, Tim C" <tim.c.chen@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
(cherry picked from commit 8afdcece4911e51cfff2b50a269418914cab8a3f)

Signed-off-by: Tim Gardner <tim.gardner@canonical.com>
---
 include/linux/swap.h |    9 +++++++++
 mm/vmscan.c          |   16 +++++++++++++---
 2 files changed, 22 insertions(+), 3 deletions(-)

diff --git a/include/linux/swap.h b/include/linux/swap.h
index 97a5514..3b454c0 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -155,6 +155,15 @@ enum {
 #define SWAP_CLUSTER_MAX 32
 #define COMPACT_CLUSTER_MAX SWAP_CLUSTER_MAX
 
+/*
+ * Ratio between the present memory in the zone and the "gap" that
+ * we're allowing kswapd to shrink in addition to the per-zone high
+ * wmark, even for zones that already have the high wmark satisfied,
+ * in order to provide better per-zone lru behavior. We are ok to
+ * spend not more than 1% of the memory for this zone balancing "gap".
+ */
+#define KSWAPD_ZONE_BALANCE_GAP_RATIO 100
+
 #define SWAP_MAP_MAX	0x3e	/* Max duplication count, in first swap_map */
 #define SWAP_MAP_BAD	0x3f	/* Note pageblock is bad, in first swap_map */
 #define SWAP_HAS_CACHE	0x40	/* Flag page is cached, in first swap_map */
diff --git a/mm/vmscan.c b/mm/vmscan.c
index a578535..f50f716 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2406,6 +2406,7 @@ loop_again:
 		for (i = 0; i <= end_zone; i++) {
 			struct zone *zone = pgdat->node_zones + i;
 			int nr_slab;
+			unsigned long balance_gap;
 
 			if (!populated_zone(zone))
 				continue;
@@ -2422,11 +2423,20 @@ loop_again:
 			mem_cgroup_soft_limit_reclaim(zone, order, sc.gfp_mask);
 
 			/*
-			 * We put equal pressure on every zone, unless one
-			 * zone has way too many pages free already.
+			 * We put equal pressure on every zone, unless
+			 * one zone has way too many pages free
+			 * already. The "too many pages" is defined
+			 * as the high wmark plus a "gap" where the
+			 * gap is either the low watermark or 1%
+			 * of the zone, whichever is smaller.
 			 */
+			balance_gap = min(low_wmark_pages(zone),
+				(zone->present_pages +
+					KSWAPD_ZONE_BALANCE_GAP_RATIO-1) /
+				KSWAPD_ZONE_BALANCE_GAP_RATIO);
 			if (!zone_watermark_ok_safe(zone, order,
-					8*high_wmark_pages(zone), end_zone, 0))
+					high_wmark_pages(zone) + balance_gap,
+					end_zone, 0))
 				shrink_zone(priority, zone, &sc);
 			reclaim_state->reclaimed_slab = 0;
 			nr_slab = shrink_slab(sc.nr_scanned, GFP_KERNEL,
-- 
1.7.0.4


From c06f51cab98ee6861846f816d334d439f384933a Mon Sep 17 00:00:00 2001
From: Mel Gorman <mgorman@suse.de>
Date: Mon, 11 Jul 2011 10:21:15 +0100
Subject: [PATCH 3/5] mm: vmscan: do not apply pressure to slab if we are not applying pressure to zone
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

BugLink: http://bugs.launchpad.net/bugs/808509

commit d7868dae893c83c50c7824bc2bc75f93d114669f

During allocator-intensive workloads, kswapd will be woken frequently
causing free memory to oscillate between the high and min watermark.  This
is expected behaviour.

When kswapd applies pressure to zones during node balancing, it checks if
the zone is above a high+balance_gap threshold.  If it is, it does not
apply pressure but it unconditionally shrinks slab on a global basis which
is excessive.  In the event kswapd is being kept awake due to a high small
unreclaimable zone, it skips zone shrinking but still calls shrink_slab().

Once pressure has been applied, the check for zone being unreclaimable is
being made before the check is made if all_unreclaimable should be set.
This miss of unreclaimable can cause has_under_min_watermark_zone to be
set due to an unreclaimable zone preventing kswapd backing off on
congestion_wait().

Signed-off-by: Mel Gorman <mgorman@suse.de>
Reported-by: Pádraig Brady <P@draigBrady.com>
Tested-by: Pádraig Brady <P@draigBrady.com>
Tested-by: Andrew Lutomirski <luto@mit.edu>
Acked-by: Rik van Riel <riel@redhat.com>
Reviewed-by: Minchan Kim <minchan.kim@gmail.com>
Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>
---
 mm/vmscan.c |   25 ++++++++++++++-----------
 1 files changed, 14 insertions(+), 11 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index f50f716..7f8e890 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2436,19 +2436,19 @@ loop_again:
 				KSWAPD_ZONE_BALANCE_GAP_RATIO);
 			if (!zone_watermark_ok_safe(zone, order,
 					high_wmark_pages(zone) + balance_gap,
-					end_zone, 0))
+					end_zone, 0)) {
 				shrink_zone(priority, zone, &sc);
-			reclaim_state->reclaimed_slab = 0;
-			nr_slab = shrink_slab(sc.nr_scanned, GFP_KERNEL,
-						lru_pages);
-			sc.nr_reclaimed += reclaim_state->reclaimed_slab;
-			total_scanned += sc.nr_scanned;
 
-			if (zone->all_unreclaimable)
-				continue;
-			if (nr_slab == 0 &&
-			    !zone_reclaimable(zone))
-				zone->all_unreclaimable = 1;
+				reclaim_state->reclaimed_slab = 0;
+				nr_slab = shrink_slab(sc.nr_scanned, GFP_KERNEL,
+							lru_pages);
+				sc.nr_reclaimed += reclaim_state->reclaimed_slab;
+				total_scanned += sc.nr_scanned;
+
+				if (nr_slab == 0 && !zone_reclaimable(zone))
+					zone->all_unreclaimable = 1;
+			}
+
 			/*
 			 * If we've done a decent amount of scanning and
 			 * the reclaim ratio is low, start doing writepage
@@ -2458,6 +2458,9 @@ loop_again:
 			    total_scanned > sc.nr_reclaimed + sc.nr_reclaimed / 2)
 				sc.may_writepage = 1;
 
+			if (zone->all_unreclaimable)
+				continue;
+
 			if (!zone_watermark_ok_safe(zone, order,
 					high_wmark_pages(zone), end_zone, 0)) {
 				all_zones_ok = 0;
-- 
1.7.0.4


From 3b9266cd8d60fb291cee6f8b8bbc6ff282f6dc20 Mon Sep 17 00:00:00 2001
From: Mel Gorman <mgorman@suse.de>
Date: Fri, 8 Jul 2011 15:39:39 -0700
Subject: [PATCH 4/5] mm: vmscan: evaluate the watermarks against the correct classzone
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

BugLink: http://bugs.launchpad.net/bugs/808509

When deciding if kswapd is sleeping prematurely, the classzone is taken
into account but this is different to what balance_pgdat() and the
allocator are doing.  Specifically, the DMA zone will be checked based on
the classzone used when waking kswapd which could be for a GFP_KERNEL or
GFP_HIGHMEM request.  The lowmem reserve limit kicks in, the watermark is
not met and kswapd thinks it's sleeping prematurely keeping kswapd awake in
error.

Signed-off-by: Mel Gorman <mgorman@suse.de>
Reported-by: Pádraig Brady <P@draigBrady.com>
Tested-by: Pádraig Brady <P@draigBrady.com>
Tested-by: Andrew Lutomirski <luto@mit.edu>
Acked-by: Rik van Riel <riel@redhat.com>
Reviewed-by: Minchan Kim <minchan.kim@gmail.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
(cherry picked from commit da175d06b437093f93109ba9e5efbe44dfdf9409)

Signed-off-by: Tim Gardner <tim.gardner@canonical.com>
---
 mm/vmscan.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 7f8e890..136dc5e 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2279,7 +2279,7 @@ static bool sleeping_prematurely(pg_data_t *pgdat, int order, long remaining,
 		}
 
 		if (!zone_watermark_ok_safe(zone, order, high_wmark_pages(zone),
-							classzone_idx, 0))
+							i, 0))
 			all_zones_ok = false;
 		else
 			balanced += zone->present_pages;
-- 
1.7.0.4


From 35b09ae93713a435cd5abe3ea54bce8ad70d4345 Mon Sep 17 00:00:00 2001
From: Mel Gorman <mgorman@suse.de>
Date: Fri, 8 Jul 2011 15:39:40 -0700
Subject: [PATCH 5/5] mm: vmscan: only read new_classzone_idx from pgdat when reclaiming successfully
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

BugLink: http://bugs.launchpad.net/bugs/808509

During allocator-intensive workloads, kswapd will be woken frequently
causing free memory to oscillate between the high and min watermark.  This
is expected behaviour.  Unfortunately, if the highest zone is small, a
problem occurs.

When balance_pgdat() returns, it may be at a lower classzone_idx than it
started because the highest zone was unreclaimable.  Before checking if it
should go to sleep though, it checks pgdat->classzone_idx which when there
is no other activity will be MAX_NR_ZONES-1.  It interprets this as it has
been woken up while reclaiming, skips scheduling and reclaims again.  As
there is no useful reclaim work to do, it enters into a loop of shrinking
slab consuming loads of CPU until the highest zone becomes reclaimable for
a long period of time.

There are two problems here.  1) If the returned classzone or order is
lower, it'll continue reclaiming without scheduling.  2) if the highest
zone was marked unreclaimable but balance_pgdat() returns immediately at
DEF_PRIORITY, the new lower classzone is not communicated back to kswapd()
for sleeping.

This patch does two things that are related.  If the end_zone is
unreclaimable, this information is communicated back.  Second, if the
classzone or order was reduced due to failing to reclaim, new information
is not read from pgdat and instead an attempt is made to go to sleep.  Due
to this, it is also necessary that pgdat->classzone_idx be initialised
each time to pgdat->nr_zones - 1 to avoid re-reads being interpreted as
wakeups.

Signed-off-by: Mel Gorman <mgorman@suse.de>
Reported-by: Pádraig Brady <P@draigBrady.com>
Tested-by: Pádraig Brady <P@draigBrady.com>
Tested-by: Andrew Lutomirski <luto@mit.edu>
Acked-by: Rik van Riel <riel@redhat.com>
Cc: Minchan Kim <minchan.kim@gmail.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
(cherry picked from commit 215ddd6664ced067afca7eebd2d1eb83f064ff5a)

Signed-off-by: Tim Gardner <tim.gardner@canonical.com>
---
 mm/vmscan.c |   34 +++++++++++++++++++++-------------
 1 files changed, 21 insertions(+), 13 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 136dc5e..4b8b37c 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2381,7 +2381,6 @@ loop_again:
 			if (!zone_watermark_ok_safe(zone, order,
 					high_wmark_pages(zone), 0, 0)) {
 				end_zone = i;
-				*classzone_idx = i;
 				break;
 			}
 		}
@@ -2458,8 +2457,11 @@ loop_again:
 			    total_scanned > sc.nr_reclaimed + sc.nr_reclaimed / 2)
 				sc.may_writepage = 1;
 
-			if (zone->all_unreclaimable)
+			if (zone->all_unreclaimable) {
+				if (end_zone && end_zone == i)
+					end_zone--;
 				continue;
+			}
 
 			if (!zone_watermark_ok_safe(zone, order,
 					high_wmark_pages(zone), end_zone, 0)) {
@@ -2639,8 +2641,8 @@ static void kswapd_try_to_sleep(pg_data_t *pgdat, int order, int classzone_idx)
  */
 static int kswapd(void *p)
 {
-	unsigned long order;
-	int classzone_idx;
+	unsigned long order, new_order;
+	int classzone_idx, new_classzone_idx;
 	pg_data_t *pgdat = (pg_data_t*)p;
 	struct task_struct *tsk = current;
 
@@ -2670,17 +2672,23 @@ static int kswapd(void *p)
 	tsk->flags |= PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD;
 	set_freezable();
 
-	order = 0;
-	classzone_idx = MAX_NR_ZONES - 1;
+	order = new_order = 0;
+	classzone_idx = new_classzone_idx = pgdat->nr_zones - 1;
 	for ( ; ; ) {
-		unsigned long new_order;
-		int new_classzone_idx;
 		int ret;
 
-		new_order = pgdat->kswapd_max_order;
-		new_classzone_idx = pgdat->classzone_idx;
-		pgdat->kswapd_max_order = 0;
-		pgdat->classzone_idx = MAX_NR_ZONES - 1;
+		/*
+		 * If the last balance_pgdat was unsuccessful it's unlikely a
+		 * new request of a similar or harder type will succeed soon
+		 * so consider going to sleep on the basis we reclaimed at
+		 */
+		if (classzone_idx >= new_classzone_idx && order == new_order) {
+			new_order = pgdat->kswapd_max_order;
+			new_classzone_idx = pgdat->classzone_idx;
+			pgdat->kswapd_max_order =  0;
+			pgdat->classzone_idx = pgdat->nr_zones - 1;
+		}
+
 		if (order < new_order || classzone_idx > new_classzone_idx) {
 			/*
 			 * Don't sleep if someone wants a larger 'order'
@@ -2693,7 +2701,7 @@ static int kswapd(void *p)
 			order = pgdat->kswapd_max_order;
 			classzone_idx = pgdat->classzone_idx;
 			pgdat->kswapd_max_order = 0;
-			pgdat->classzone_idx = MAX_NR_ZONES - 1;
+			pgdat->classzone_idx = pgdat->nr_zones - 1;
 		}
 
 		ret = try_to_freeze();
