[PATCH 11/14] page-replace-move-refill.patch

[Peter Zijlstra <a.p.zijlstra@chello.nl>]

From: Peter Zijlstra <a.p.zijlstra@chello.nl>

Move refill_inactive_page() to the new mm/page_replace.c file. And
couple its invocation to the: page_replace_candidate() function.
Keep the scan-rate equal to nr_active/nr_inactive. Also make sure
we only scan in full multiples of swap_cluster_max.

Kudos to Wu Fengguang for showing me the way to decouple the active
and inactive scans.

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

 include/linux/mm_page_replace.h |    2 
 include/linux/mmzone.h          |    1 
 mm/page_alloc.c                 |    4 
 mm/page_replace.c               |  180 ++++++++++++++++++++++++++++++++++++
 mm/vmscan.c                     |  196 ++--------------------------------------
 5 files changed, 189 insertions(+), 194 deletions(-)

Index: linux-2.6-git/mm/page_replace.c
===================================================================
--- linux-2.6-git.orig/mm/page_replace.c
+++ linux-2.6-git/mm/page_replace.c
@@ -1,6 +1,27 @@
 #include <linux/mm_page_replace.h>
 #include <linux/swap.h>
 #include <linux/pagevec.h>
+#include <linux/page-flags.h>
+#include <linux/init.h>
+#include <linux/rmap.h>
+#include <linux/buffer_head.h>	/* for try_to_release_page(),
+					buffer_heads_over_limit */
+
+/*
+ * From 0 .. 100.  Higher means more swappy.
+ */
+int vm_swappiness = 60;
+static long total_memory;
+
+static void refill_inactive_zone(struct zone *, int);
+
+static int __init page_replace_init(void)
+{
+	total_memory = nr_free_pagecache_pages();
+	return 0;
+}
+
+module_init(page_replace_init)
 
 static inline void
 add_page_to_inactive_list(struct zone *zone, struct page *page)
@@ -34,8 +55,8 @@ void __page_replace_insert(struct zone *
  *
  * returns how many pages were moved onto *@dst.
  */
-int isolate_lru_pages(int nr_to_scan, struct list_head *src,
-		      struct list_head *dst, int *scanned)
+static int isolate_lru_pages(int nr_to_scan, struct list_head *src,
+			     struct list_head *dst, int *scanned)
 {
 	int nr_taken = 0;
 	struct page *page;
@@ -70,6 +91,7 @@ void page_replace_candidates(struct zone
 {
 	int nr_taken;
 	int nr_scan;
+	unsigned long long nr_scan_active;
 
 	spin_lock_irq(&zone->lru_lock);
 	nr_taken = isolate_lru_pages(nr_to_scan, &zone->inactive_list,
@@ -82,6 +104,18 @@ void page_replace_candidates(struct zone
 		mod_page_state_zone(zone, pgscan_kswapd, nr_scan);
 	else
 		mod_page_state_zone(zone, pgscan_direct, nr_scan);
+
+	/*
+	 * Add one to `nr_to_scan' just to make sure that the kernel will
+	 * slowly sift through the active list.
+	 */
+	nr_scan_active = (nr_scan + 1ULL) * zone->nr_active * 1024ULL;
+	do_div(nr_scan_active, zone->nr_inactive + nr_taken + 1UL);
+	zone->nr_scan_active += nr_scan_active;
+	while (zone->nr_scan_active >= SWAP_CLUSTER_MAX * 1024UL) {
+		zone->nr_scan_active -= SWAP_CLUSTER_MAX * 1024UL;
+		refill_inactive_zone(zone, SWAP_CLUSTER_MAX);
+	}
 }
 
 /*
@@ -112,3 +146,145 @@ void page_replace_reinsert(struct zone *
 	pagevec_release(&pvec);
 }
 
+/*
+ * This moves pages from the active list to the inactive list.
+ *
+ * We move them the other way if the page is referenced by one or more
+ * processes, from rmap.
+ *
+ * If the pages are mostly unmapped, the processing is fast and it is
+ * appropriate to hold zone->lru_lock across the whole operation.  But if
+ * the pages are mapped, the processing is slow (page_referenced()) so we
+ * should drop zone->lru_lock around each page.  It's impossible to balance
+ * this, so instead we remove the pages from the LRU while processing them.
+ * It is safe to rely on PG_active against the non-LRU pages in here because
+ * nobody will play with that bit on a non-LRU page.
+ *
+ * The downside is that we have to touch page->_count against each page.
+ * But we had to alter page->flags anyway.
+ */
+static void refill_inactive_zone(struct zone *zone, int nr_pages)
+{
+	int pgmoved;
+	int pgdeactivate = 0;
+	int pgscanned;
+	LIST_HEAD(l_hold);	/* The pages which were snipped off */
+	LIST_HEAD(l_inactive);	/* Pages to go onto the inactive_list */
+	LIST_HEAD(l_active);	/* Pages to go onto the active_list */
+	struct page *page;
+	struct pagevec pvec;
+	int reclaim_mapped = 0;
+	long mapped_ratio;
+	long distress;
+	long swap_tendency;
+
+	lru_add_drain();
+	spin_lock_irq(&zone->lru_lock);
+	pgmoved = isolate_lru_pages(nr_pages, &zone->active_list,
+				    &l_hold, &pgscanned);
+	zone->pages_scanned += pgscanned;
+	zone->nr_active -= pgmoved;
+	spin_unlock_irq(&zone->lru_lock);
+
+	/*
+	 * `distress' is a measure of how much trouble we're having reclaiming
+	 * pages.  0 -> no problems.  100 -> great trouble.
+	 */
+	distress = 100 >> zone->prev_priority;
+
+	/*
+	 * The point of this algorithm is to decide when to start reclaiming
+	 * mapped memory instead of just pagecache.  Work out how much memory
+	 * is mapped.
+	 */
+	mapped_ratio = (read_page_state(nr_mapped) * 100) / total_memory;
+
+	/*
+	 * Now decide how much we really want to unmap some pages.  The mapped
+	 * ratio is downgraded - just because there's a lot of mapped memory
+	 * doesn't necessarily mean that page reclaim isn't succeeding.
+	 *
+	 * The distress ratio is important - we don't want to start going oom.
+	 *
+	 * A 100% value of vm_swappiness overrides this algorithm altogether.
+	 */
+	swap_tendency = mapped_ratio / 2 + distress + vm_swappiness;
+
+	/*
+	 * Now use this metric to decide whether to start moving mapped memory
+	 * onto the inactive list.
+	 */
+	if (swap_tendency >= 100)
+		reclaim_mapped = 1;
+
+	while (!list_empty(&l_hold)) {
+		cond_resched();
+		page = lru_to_page(&l_hold);
+		list_del(&page->lru);
+		if (page_mapped(page)) {
+			if (!reclaim_mapped ||
+			    (total_swap_pages == 0 && PageAnon(page)) ||
+			    page_referenced(page, 0)) {
+				list_add(&page->lru, &l_active);
+				continue;
+			}
+		}
+		list_add(&page->lru, &l_inactive);
+	}
+
+	pagevec_init(&pvec, 1);
+	pgmoved = 0;
+	spin_lock_irq(&zone->lru_lock);
+	while (!list_empty(&l_inactive)) {
+		page = lru_to_page(&l_inactive);
+		prefetchw_prev_lru_page(page, &l_inactive, flags);
+		if (TestSetPageLRU(page))
+			BUG();
+		if (!TestClearPageActive(page))
+			BUG();
+		list_move(&page->lru, &zone->inactive_list);
+		pgmoved++;
+		if (!pagevec_add(&pvec, page)) {
+			zone->nr_inactive += pgmoved;
+			spin_unlock_irq(&zone->lru_lock);
+			pgdeactivate += pgmoved;
+			pgmoved = 0;
+			if (buffer_heads_over_limit)
+				pagevec_strip(&pvec);
+			__pagevec_release(&pvec);
+			spin_lock_irq(&zone->lru_lock);
+		}
+	}
+	zone->nr_inactive += pgmoved;
+	pgdeactivate += pgmoved;
+	if (buffer_heads_over_limit) {
+		spin_unlock_irq(&zone->lru_lock);
+		pagevec_strip(&pvec);
+		spin_lock_irq(&zone->lru_lock);
+	}
+
+	pgmoved = 0;
+	while (!list_empty(&l_active)) {
+		page = lru_to_page(&l_active);
+		prefetchw_prev_lru_page(page, &l_active, flags);
+		if (TestSetPageLRU(page))
+			BUG();
+		BUG_ON(!PageActive(page));
+		list_move(&page->lru, &zone->active_list);
+		pgmoved++;
+		if (!pagevec_add(&pvec, page)) {
+			zone->nr_active += pgmoved;
+			pgmoved = 0;
+			spin_unlock_irq(&zone->lru_lock);
+			__pagevec_release(&pvec);
+			spin_lock_irq(&zone->lru_lock);
+		}
+	}
+	zone->nr_active += pgmoved;
+	spin_unlock_irq(&zone->lru_lock);
+	pagevec_release(&pvec);
+
+	mod_page_state_zone(zone, pgrefill, pgscanned);
+	mod_page_state(pgdeactivate, pgdeactivate);
+}
+
Index: linux-2.6-git/mm/vmscan.c
===================================================================
--- linux-2.6-git.orig/mm/vmscan.c
+++ linux-2.6-git/mm/vmscan.c
@@ -103,12 +103,6 @@ struct shrinker {
 	long			nr;	/* objs pending delete */
 };
 
-/*
- * From 0 .. 100.  Higher means more swappy.
- */
-int vm_swappiness = 60;
-static long total_memory;
-
 static LIST_HEAD(shrinker_list);
 static DECLARE_RWSEM(shrinker_rwsem);
 
@@ -590,200 +584,31 @@ static void shrink_cache(struct zone *zo
 }
 
 /*
- * This moves pages from the active list to the inactive list.
- *
- * We move them the other way if the page is referenced by one or more
- * processes, from rmap.
- *
- * If the pages are mostly unmapped, the processing is fast and it is
- * appropriate to hold zone->lru_lock across the whole operation.  But if
- * the pages are mapped, the processing is slow (page_referenced()) so we
- * should drop zone->lru_lock around each page.  It's impossible to balance
- * this, so instead we remove the pages from the LRU while processing them.
- * It is safe to rely on PG_active against the non-LRU pages in here because
- * nobody will play with that bit on a non-LRU page.
- *
- * The downside is that we have to touch page->_count against each page.
- * But we had to alter page->flags anyway.
- */
-static void
-refill_inactive_zone(struct zone *zone, int nr_pages)
-{
-	int pgmoved;
-	int pgdeactivate = 0;
-	int pgscanned;
-	LIST_HEAD(l_hold);	/* The pages which were snipped off */
-	LIST_HEAD(l_inactive);	/* Pages to go onto the inactive_list */
-	LIST_HEAD(l_active);	/* Pages to go onto the active_list */
-	struct page *page;
-	struct pagevec pvec;
-	int reclaim_mapped = 0;
-	long mapped_ratio;
-	long distress;
-	long swap_tendency;
-
-	lru_add_drain();
-	spin_lock_irq(&zone->lru_lock);
-	pgmoved = isolate_lru_pages(nr_pages, &zone->active_list,
-				    &l_hold, &pgscanned);
-	zone->pages_scanned += pgscanned;
-	zone->nr_active -= pgmoved;
-	spin_unlock_irq(&zone->lru_lock);
-
-	/*
-	 * `distress' is a measure of how much trouble we're having reclaiming
-	 * pages.  0 -> no problems.  100 -> great trouble.
-	 */
-	distress = 100 >> zone->prev_priority;
-
-	/*
-	 * The point of this algorithm is to decide when to start reclaiming
-	 * mapped memory instead of just pagecache.  Work out how much memory
-	 * is mapped.
-	 */
-	mapped_ratio = (read_page_state(nr_mapped) * 100) / total_memory;
-
-	/*
-	 * Now decide how much we really want to unmap some pages.  The mapped
-	 * ratio is downgraded - just because there's a lot of mapped memory
-	 * doesn't necessarily mean that page reclaim isn't succeeding.
-	 *
-	 * The distress ratio is important - we don't want to start going oom.
-	 *
-	 * A 100% value of vm_swappiness overrides this algorithm altogether.
-	 */
-	swap_tendency = mapped_ratio / 2 + distress + vm_swappiness;
-
-	/*
-	 * Now use this metric to decide whether to start moving mapped memory
-	 * onto the inactive list.
-	 */
-	if (swap_tendency >= 100)
-		reclaim_mapped = 1;
-
-	while (!list_empty(&l_hold)) {
-		cond_resched();
-		page = lru_to_page(&l_hold);
-		list_del(&page->lru);
-		if (page_mapped(page)) {
-			if (!reclaim_mapped ||
-			    (total_swap_pages == 0 && PageAnon(page)) ||
-			    page_referenced(page, 0)) {
-				list_add(&page->lru, &l_active);
-				continue;
-			}
-		}
-		list_add(&page->lru, &l_inactive);
-	}
-
-	pagevec_init(&pvec, 1);
-	pgmoved = 0;
-	spin_lock_irq(&zone->lru_lock);
-	while (!list_empty(&l_inactive)) {
-		page = lru_to_page(&l_inactive);
-		prefetchw_prev_lru_page(page, &l_inactive, flags);
-		if (TestSetPageLRU(page))
-			BUG();
-		if (!TestClearPageActive(page))
-			BUG();
-		list_move(&page->lru, &zone->inactive_list);
-		pgmoved++;
-		if (!pagevec_add(&pvec, page)) {
-			zone->nr_inactive += pgmoved;
-			spin_unlock_irq(&zone->lru_lock);
-			pgdeactivate += pgmoved;
-			pgmoved = 0;
-			if (buffer_heads_over_limit)
-				pagevec_strip(&pvec);
-			__pagevec_release(&pvec);
-			spin_lock_irq(&zone->lru_lock);
-		}
-	}
-	zone->nr_inactive += pgmoved;
-	pgdeactivate += pgmoved;
-	if (buffer_heads_over_limit) {
-		spin_unlock_irq(&zone->lru_lock);
-		pagevec_strip(&pvec);
-		spin_lock_irq(&zone->lru_lock);
-	}
-
-	pgmoved = 0;
-	while (!list_empty(&l_active)) {
-		page = lru_to_page(&l_active);
-		prefetchw_prev_lru_page(page, &l_active, flags);
-		if (TestSetPageLRU(page))
-			BUG();
-		BUG_ON(!PageActive(page));
-		list_move(&page->lru, &zone->active_list);
-		pgmoved++;
-		if (!pagevec_add(&pvec, page)) {
-			zone->nr_active += pgmoved;
-			pgmoved = 0;
-			spin_unlock_irq(&zone->lru_lock);
-			__pagevec_release(&pvec);
-			spin_lock_irq(&zone->lru_lock);
-		}
-	}
-	zone->nr_active += pgmoved;
-	spin_unlock_irq(&zone->lru_lock);
-	pagevec_release(&pvec);
-
-	mod_page_state_zone(zone, pgrefill, pgscanned);
-	mod_page_state(pgdeactivate, pgdeactivate);
-}
-
-/*
  * This is a basic per-zone page freer.  Used by both kswapd and direct reclaim.
  */
 static void
 shrink_zone(struct zone *zone, struct scan_control *sc)
 {
-	unsigned long nr_active;
 	unsigned long nr_inactive;
 
 	atomic_inc(&zone->reclaim_in_progress);
 
-	/*
-	 * Add one to `nr_to_scan' just to make sure that the kernel will
-	 * slowly sift through the active list.
-	 */
-	zone->nr_scan_active += (zone->nr_active >> sc->priority) + 1;
-	nr_active = zone->nr_scan_active;
-	if (nr_active >= sc->swap_cluster_max)
-		zone->nr_scan_active = 0;
-	else
-		nr_active = 0;
-
-	zone->nr_scan_inactive += (zone->nr_inactive >> sc->priority) + 1;
-	nr_inactive = zone->nr_scan_inactive;
-	if (nr_inactive >= sc->swap_cluster_max)
-		zone->nr_scan_inactive = 0;
-	else
-		nr_inactive = 0;
+	nr_inactive = (zone->nr_inactive >> sc->priority) + SWAP_CLUSTER_MAX;
+	nr_inactive &= ~(SWAP_CLUSTER_MAX - 1);
 
+	sc->nr_to_scan = SWAP_CLUSTER_MAX;
 	sc->nr_to_reclaim = sc->swap_cluster_max;
 
-	while (nr_active || nr_inactive) {
-		if (nr_active) {
-			sc->nr_to_scan = min(nr_active,
-					(unsigned long)sc->swap_cluster_max);
-			nr_active -= sc->nr_to_scan;
-			refill_inactive_zone(zone, sc->nr_to_scan);
-		}
-
-		if (nr_inactive) {
-			sc->nr_to_scan = min(nr_inactive,
-					(unsigned long)sc->swap_cluster_max);
-			nr_inactive -= sc->nr_to_scan;
-			shrink_cache(zone, sc);
-			if (sc->nr_to_reclaim <= 0)
-				break;
-		}
+	while (nr_inactive >= SWAP_CLUSTER_MAX) {
+		nr_inactive -= SWAP_CLUSTER_MAX;
+		shrink_cache(zone, sc);
+		if (sc->nr_to_reclaim <= 0)
+			break;
 	}
 
-	throttle_vm_writeout();
-
 	atomic_dec(&zone->reclaim_in_progress);
+
+	throttle_vm_writeout();
 }
 
 /*
@@ -1245,7 +1070,6 @@ static int __init kswapd_init(void)
 	for_each_pgdat(pgdat)
 		pgdat->kswapd
 		= find_task_by_pid(kernel_thread(kswapd, pgdat, CLONE_KERNEL));
-	total_memory = nr_free_pagecache_pages();
 	hotcpu_notifier(cpu_callback, 0);
 	return 0;
 }
Index: linux-2.6-git/include/linux/mm_page_replace.h
===================================================================
--- linux-2.6-git.orig/include/linux/mm_page_replace.h
+++ linux-2.6-git/include/linux/mm_page_replace.h
@@ -45,8 +45,6 @@ static inline void page_replace_activate
 }
 void page_replace_reinsert(struct zone *, struct list_head *);
 
-int isolate_lru_pages(int, struct list_head *, struct list_head *, int *);
-
 static inline void
 add_page_to_active_list(struct zone *zone, struct page *page)
 {
Index: linux-2.6-git/include/linux/mmzone.h
===================================================================
--- linux-2.6-git.orig/include/linux/mmzone.h
+++ linux-2.6-git/include/linux/mmzone.h
@@ -144,7 +144,6 @@ struct zone {
 	struct list_head	active_list;
 	struct list_head	inactive_list;
 	unsigned long		nr_scan_active;
-	unsigned long		nr_scan_inactive;
 	unsigned long		nr_active;
 	unsigned long		nr_inactive;
 	unsigned long		pages_scanned;	   /* since last reclaim */
Index: linux-2.6-git/mm/page_alloc.c
===================================================================
--- linux-2.6-git.orig/mm/page_alloc.c
+++ linux-2.6-git/mm/page_alloc.c
@@ -2010,7 +2010,6 @@ static void __init free_area_init_core(s
 		INIT_LIST_HEAD(&zone->active_list);
 		INIT_LIST_HEAD(&zone->inactive_list);
 		zone->nr_scan_active = 0;
-		zone->nr_scan_inactive = 0;
 		zone->nr_active = 0;
 		zone->nr_inactive = 0;
 		atomic_set(&zone->reclaim_in_progress, 0);
@@ -2161,7 +2160,7 @@ static int zoneinfo_show(struct seq_file
 			   "\n        high     %lu"
 			   "\n        active   %lu"
 			   "\n        inactive %lu"
-			   "\n        scanned  %lu (a: %lu i: %lu)"
+			   "\n        scanned  %lu"
 			   "\n        spanned  %lu"
 			   "\n        present  %lu",
 			   zone->free_pages,
@@ -2171,7 +2170,6 @@ static int zoneinfo_show(struct seq_file
 			   zone->nr_active,
 			   zone->nr_inactive,
 			   zone->pages_scanned,
-			   zone->nr_scan_active, zone->nr_scan_inactive,
 			   zone->spanned_pages,
 			   zone->present_pages);
 		seq_printf(m,

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