[PATCH 0/4] Lumpy Reclaim V3

[PATCH 0/4] Lumpy Reclaim V3

[Andy Whitcroft]

Some weeks back I posted a linear reclaim patch series.  Discussions
on that led Peter Zijlstra to propose new simpler block based reclaim
algorithm called 'lumpy'.  We have been testing variants of this to
try and improve its effectivness to close to that of the heavier
weight linear algorithm.  The stack below both remains simple but
gives us pretty useful reclaim rates.

I have left the changes broken out for the time being so as to make
it clear what is the original and what is my fault.  I would expect
to roll this up before acceptance.

-apw

=== 8< ===
Lumpy Reclaim (V3)

When we are out of memory of a suitable size we enter reclaim.
The current reclaim algorithm targets pages in LRU order, which
is great for fairness but highly unsuitable if you desire pages at
higher orders.  To get pages of higher order we must shoot down a
very high proportion of memory; >95% in a lot of cases.

This patch set adds a lumpy reclaim algorithm to the allocator.
It targets groups of pages at the specified order anchored at the
end of the active and inactive lists.  This encourages groups of
pages at the requested orders to move from active to inactive,
and active to free lists.  This behaviour is only triggered out of
direct reclaim when higher order pages have been requested.

This patch set is particularly effective when utilised with
an anti-fragmentation scheme which groups pages of similar
reclaimability together.

This patch set (against 2.6.19-rc5-mm2) is based on Peter Zijlstra's
lumpy reclaim V2 patch which forms the foundation.  It comprises
the following patches:

lumpy-reclaim-v2 -- Peter Zijlstra's lumpy reclaim prototype,

lumpy-cleanup-a-missplaced-comment-and-simplify-some-code --
  cleanups to move a comment back to where it came from, to make
  the area edge selection more comprehensible and also cleans up
  the switch coding style to match the concensus in mm/*.c,

lumpy-ensure-we-respect-zone-boundaries -- bug fix to ensure we do
  not attempt to take pages from adjacent zones, and

lumpy-take-the-other-active-inactive-pages-in-the-area -- patch to
  increase aggression over the targetted order.

Testing of this patch set under high fragmentation high allocation
load conditions shows significantly improved high order reclaim
rates than a standard kernel.  The stack here it is now within 5%
of the best case linear-reclaim figures.

It would be interesting to see if this setup is also successful in
reducing order-2 allocation failures that you have been seeing with
jumbo frames.

Please consider for -mm.

-apw

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>

[PATCH 1/4] lumpy reclaim v2

[Andy Whitcroft]

lumpy reclaim v2

When trying to reclaim pages for a higher order allocation, make reclaim
try to move lumps of pages (fitting the requested order) about, instead
of single pages. This should significantly reduce the number of
reclaimed pages for higher order allocations.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Andy Whitcroft <apw@shadowen.org>
---
diff --git a/fs/buffer.c b/fs/buffer.c
index 64ea099..c73acb7 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -424,7 +424,7 @@ static void free_more_memory(void)
 	for_each_online_pgdat(pgdat) {
 		zones = pgdat->node_zonelists[gfp_zone(GFP_NOFS)].zones;
 		if (*zones)
-			try_to_free_pages(zones, GFP_NOFS);
+			try_to_free_pages(zones, 0, GFP_NOFS);
 	}
 }
 
diff --git a/include/linux/swap.h b/include/linux/swap.h
index 439f9a8..5c26736 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -187,7 +187,7 @@ extern int rotate_reclaimable_page(struc
 extern void swap_setup(void);
 
 /* linux/mm/vmscan.c */
-extern unsigned long try_to_free_pages(struct zone **, gfp_t);
+extern unsigned long try_to_free_pages(struct zone **, int, gfp_t);
 extern unsigned long shrink_all_memory(unsigned long nr_pages);
 extern int vm_swappiness;
 extern int remove_mapping(struct address_space *mapping, struct page *page);
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 19ab611..39f48a8 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1368,7 +1368,7 @@ nofail_alloc:
 	reclaim_state.reclaimed_slab = 0;
 	p->reclaim_state = &reclaim_state;
 
-	did_some_progress = try_to_free_pages(zonelist->zones, gfp_mask);
+	did_some_progress = try_to_free_pages(zonelist->zones, order, gfp_mask);
 
 	p->reclaim_state = NULL;
 	p->flags &= ~PF_MEMALLOC;
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 7e9caff..4645a3f 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -67,6 +67,8 @@ struct scan_control {
 	int swappiness;
 
 	int all_unreclaimable;
+
+	int order;
 };
 
 #define lru_to_page(_head) (list_entry((_head)->prev, struct page, lru))
@@ -623,35 +625,86 @@ keep:
  *
  * returns how many pages were moved onto *@dst.
  */
+int __isolate_lru_page(struct page *page, int active)
+{
+	int ret = -EINVAL;
+
+	if (PageLRU(page) && (PageActive(page) == active)) {
+		ret = -EBUSY;
+		if (likely(get_page_unless_zero(page))) {
+			/*
+			 * Be careful not to clear PageLRU until after we're
+			 * sure the page is not being freed elsewhere -- the
+			 * page release code relies on it.
+			 */
+			ClearPageLRU(page);
+			ret = 0;
+		}
+	}
+
+	return ret;
+}
+
 static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
 		struct list_head *src, struct list_head *dst,
-		unsigned long *scanned)
+		unsigned long *scanned, int order)
 {
 	unsigned long nr_taken = 0;
-	struct page *page;
-	unsigned long scan;
+	struct page *page, *tmp;
+	unsigned long scan, pfn, end_pfn, page_pfn;
+	int active;
 
 	for (scan = 0; scan < nr_to_scan && !list_empty(src); scan++) {
-		struct list_head *target;
 		page = lru_to_page(src);
 		prefetchw_prev_lru_page(page, src, flags);
 
 		VM_BUG_ON(!PageLRU(page));
 
-		list_del(&page->lru);
-		target = src;
-		if (likely(get_page_unless_zero(page))) {
-			/*
-			 * Be careful not to clear PageLRU until after we're
-			 * sure the page is not being freed elsewhere -- the
-			 * page release code relies on it.
-			 */
-			ClearPageLRU(page);
-			target = dst;
-			nr_taken++;
-		} /* else it is being freed elsewhere */
+		active = PageActive(page);
+		switch (__isolate_lru_page(page, active)) {
+			case 0:
+				list_move(&page->lru, dst);
+				nr_taken++;
+				break;
+
+			case -EBUSY:
+				/* else it is being freed elsewhere */
+				list_move(&page->lru, src);
+				continue;
+
+			default:
+				BUG();
+		}
 
-		list_add(&page->lru, target);
+		if (!order)
+			continue;
+
+		page_pfn = pfn = __page_to_pfn(page);
+		end_pfn = pfn &= ~((1 << order) - 1);
+		end_pfn += 1 << order;
+		for (; pfn < end_pfn; pfn++) {
+			if (unlikely(pfn == page_pfn))
+				continue;
+			if (unlikely(!pfn_valid(pfn)))
+				break;
+
+			scan++;
+			tmp = __pfn_to_page(pfn);
+			switch (__isolate_lru_page(tmp, active)) {
+				case 0:
+					list_move(&tmp->lru, dst);
+					nr_taken++;
+					continue;
+
+				case -EBUSY:
+					/* else it is being freed elsewhere */
+					list_move(&tmp->lru, src);
+				default:
+					break;
+
+			}
+			break;
+		}
 	}
 
 	*scanned = scan;
@@ -682,7 +735,7 @@ static unsigned long shrink_inactive_lis
 
 		nr_taken = isolate_lru_pages(sc->swap_cluster_max,
 					     &zone->inactive_list,
-					     &page_list, &nr_scan);
+					     &page_list, &nr_scan, sc->order);
 		zone->nr_inactive -= nr_taken;
 		zone->pages_scanned += nr_scan;
 		zone->aging_total += nr_scan;
@@ -828,7 +881,7 @@ force_reclaim_mapped:
 	lru_add_drain();
 	spin_lock_irq(&zone->lru_lock);
 	pgmoved = isolate_lru_pages(nr_pages, &zone->active_list,
-				    &l_hold, &pgscanned);
+				    &l_hold, &pgscanned, sc->order);
 	zone->pages_scanned += pgscanned;
 	zone->nr_active -= pgmoved;
 	spin_unlock_irq(&zone->lru_lock);
@@ -1017,7 +1070,7 @@ static unsigned long shrink_zones(int pr
  * holds filesystem locks which prevent writeout this might not work, and the
  * allocation attempt will fail.
  */
-unsigned long try_to_free_pages(struct zone **zones, gfp_t gfp_mask)
+unsigned long try_to_free_pages(struct zone **zones, int order, gfp_t gfp_mask)
 {
 	int priority;
 	int ret = 0;
@@ -1032,6 +1085,7 @@ unsigned long try_to_free_pages(struct z
 		.swap_cluster_max = SWAP_CLUSTER_MAX,
 		.may_swap = 1,
 		.swappiness = vm_swappiness,
+		.order = order,
 	};
 
 	delay_swap_prefetch();

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>

[PATCH 2/4] lumpy cleanup a missplaced comment and simplify some code

[Andy Whitcroft]

Move the comment for isolate_lru_pages() back to its function
and comment the new function.  Add some running commentry on the
area scan.  Cleanup the indentation on switch to match the majority
view in mm/*.  Finally, clarify the boundary pfn calculations.

Signed-off-by: Andy Whitcroft <apw@shadowen.org>
---
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 4645a3f..3b6ef79 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -609,21 +609,14 @@ keep:
 }
 
 /*
- * zone->lru_lock is heavily contended.  Some of the functions that
- * shrink the lists perform better by taking out a batch of pages
- * and working on them outside the LRU lock.
+ * Attempt to remove the specified page from its LRU.  Only take this
+ * page if it is of the appropriate PageActive status.  Pages which
+ * are being freed elsewhere are also ignored.
  *
- * For pagecache intensive workloads, this function is the hottest
- * spot in the kernel (apart from copy_*_user functions).
- *
- * Appropriate locks must be held before calling this function.
+ * @page:	page to consider
+ * @active:	active/inactive flag only take pages of this type
  *
- * @nr_to_scan:	The number of pages to look through on the list.
- * @src:	The LRU list to pull pages off.
- * @dst:	The temp list to put pages on to.
- * @scanned:	The number of pages that were scanned.
- *
- * returns how many pages were moved onto *@dst.
+ * returns 0 on success, -ve errno on failure.
  */
 int __isolate_lru_page(struct page *page, int active)
 {
@@ -645,6 +638,23 @@ int __isolate_lru_page(struct page *page
 	return ret;
 }
 
+/*
+ * zone->lru_lock is heavily contended.  Some of the functions that
+ * shrink the lists perform better by taking out a batch of pages
+ * and working on them outside the LRU lock.
+ *
+ * For pagecache intensive workloads, this function is the hottest
+ * spot in the kernel (apart from copy_*_user functions).
+ *
+ * Appropriate locks must be held before calling this function.
+ *
+ * @nr_to_scan:	The number of pages to look through on the list.
+ * @src:	The LRU list to pull pages off.
+ * @dst:	The temp list to put pages on to.
+ * @scanned:	The number of pages that were scanned.
+ *
+ * returns how many pages were moved onto *@dst.
+ */
 static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
 		struct list_head *src, struct list_head *dst,
 		unsigned long *scanned, int order)
@@ -662,26 +672,31 @@ static unsigned long isolate_lru_pages(u
 
 		active = PageActive(page);
 		switch (__isolate_lru_page(page, active)) {
-			case 0:
-				list_move(&page->lru, dst);
-				nr_taken++;
-				break;
+		case 0:
+			list_move(&page->lru, dst);
+			nr_taken++;
+			break;
 
-			case -EBUSY:
-				/* else it is being freed elsewhere */
-				list_move(&page->lru, src);
-				continue;
+		case -EBUSY:
+			/* else it is being freed elsewhere */
+			list_move(&page->lru, src);
+			continue;
 
-			default:
-				BUG();
+		default:
+			BUG();
 		}
 
 		if (!order)
 			continue;
 
-		page_pfn = pfn = __page_to_pfn(page);
-		end_pfn = pfn &= ~((1 << order) - 1);
-		end_pfn += 1 << order;
+		/*
+		 * Attempt to take all pages in the order aligned region
+		 * surrounding the tag page.  Only take those pages of
+		 * the same active state as that tag page.
+		 */
+		page_pfn = __page_to_pfn(page);
+		pfn = page_pfn & ~((1 << order) - 1);
+		end_pfn = pfn + (1 << order);
 		for (; pfn < end_pfn; pfn++) {
 			if (unlikely(pfn == page_pfn))
 				continue;
@@ -691,17 +706,16 @@ static unsigned long isolate_lru_pages(u
 			scan++;
 			tmp = __pfn_to_page(pfn);
 			switch (__isolate_lru_page(tmp, active)) {
-				case 0:
-					list_move(&tmp->lru, dst);
-					nr_taken++;
-					continue;
-
-				case -EBUSY:
-					/* else it is being freed elsewhere */
-					list_move(&tmp->lru, src);
-				default:
-					break;
+			case 0:
+				list_move(&tmp->lru, dst);
+				nr_taken++;
+				continue;
 
+			case -EBUSY:
+				/* else it is being freed elsewhere */
+				list_move(&tmp->lru, src);
+			default:
+				break;
 			}
 			break;
 		}

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>

[PATCH 3/4] lumpy ensure we respect zone boundaries

[Andy Whitcroft]

When scanning an aligned order N area ensure we only pull out pages
in the same zone as our tag page, else we will manipulate those
pages' LRU under the wrong zone lru_lock.  Bad.

Signed-off-by: Andy Whitcroft <apw@shadowen.org>
---
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 3b6ef79..e3be888 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -663,6 +663,7 @@ static unsigned long isolate_lru_pages(u
 	struct page *page, *tmp;
 	unsigned long scan, pfn, end_pfn, page_pfn;
 	int active;
+	int zone_id;
 
 	for (scan = 0; scan < nr_to_scan && !list_empty(src); scan++) {
 		page = lru_to_page(src);
@@ -694,6 +695,7 @@ static unsigned long isolate_lru_pages(u
 		 * surrounding the tag page.  Only take those pages of
 		 * the same active state as that tag page.
 		 */
+		zone_id = page_zone_id(page);
 		page_pfn = __page_to_pfn(page);
 		pfn = page_pfn & ~((1 << order) - 1);
 		end_pfn = pfn + (1 << order);
@@ -703,8 +705,10 @@ static unsigned long isolate_lru_pages(u
 			if (unlikely(!pfn_valid(pfn)))
 				break;
 
-			scan++;
 			tmp = __pfn_to_page(pfn);
+			if (unlikely(page_zone_id(tmp) != zone_id))
+				continue;
+			scan++;
 			switch (__isolate_lru_page(tmp, active)) {
 			case 0:
 				list_move(&tmp->lru, dst);

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>

[PATCH 4/4] lumpy take the other active inactive pages in the area

[Andy Whitcroft]

When we scan an order N aligned area around our tag page take any
other pages with a matching active state to that of the tag page.
This will tend to demote areas of the order we are interested from
the active list to the inactive list and from the end of the inactive
list, increasing the chances of such areas coming free together.

Signed-off-by: Andy Whitcroft <apw@shadowen.org>
---
diff --git a/mm/vmscan.c b/mm/vmscan.c
index e3be888..50e95ed 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -713,7 +713,7 @@ static unsigned long isolate_lru_pages(u
 			case 0:
 				list_move(&tmp->lru, dst);
 				nr_taken++;
-				continue;
+				break;
 
 			case -EBUSY:
 				/* else it is being freed elsewhere */
@@ -721,7 +721,6 @@ static unsigned long isolate_lru_pages(u
 			default:
 				break;
 			}
-			break;
 		}
 	}
 

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>

Re: [PATCH 0/4] Lumpy Reclaim V3

[Peter Zijlstra]

On Thu, 2006-11-23 at 16:48 +0000, Andy Whitcroft wrote:

> lumpy-reclaim-v2 -- Peter Zijlstra's lumpy reclaim prototype,
> 
> lumpy-cleanup-a-missplaced-comment-and-simplify-some-code --
>   cleanups to move a comment back to where it came from, to make
>   the area edge selection more comprehensible and also cleans up
>   the switch coding style to match the concensus in mm/*.c,

Sure looks better.

> lumpy-ensure-we-respect-zone-boundaries -- bug fix to ensure we do
>   not attempt to take pages from adjacent zones, and

Valid case I guess :-)

> lumpy-take-the-other-active-inactive-pages-in-the-area -- patch to
>   increase aggression over the targetted order.

Yeah, I see how this will help.

Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>

for all 3

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>

[PATCH 4/4] lumpy take the other active inactive pages in the area

[Andy Whitcroft]

When we scan an order N aligned area around our tag page take any
other pages with a matching active state to that of the tag page.
This will tend to demote areas of the order we are interested from
the active list to the inactive list and from the end of the inactive
list, increasing the chances of such areas coming free together.

Signed-off-by: Andy Whitcroft <apw@shadowen.org>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
---
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 85f626b..fc23d87 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -710,7 +710,7 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
 			case 0:
 				list_move(&tmp->lru, dst);
 				nr_taken++;
-				continue;
+				break;
 
 			case -EBUSY:
 				/* else it is being freed elsewhere */
@@ -718,7 +718,6 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
 			default:
 				break;
 			}
-			break;
 		}
 	}
 

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>