[RFC PATCH 2/10] free swap space entries if vm_swap_full()

[Rik van Riel]

Rik van Riel's patch to free swap space on swap-in/activiation,
forward ported by Lee Schermerhorn.

Against:  2.6.23-rc2-mm2 atop:
+ lts' convert anon_vma list lock to reader/write lock patch
+ Nick Piggin's move and rework isolate_lru_page() patch

Patch Description:  quick attempt by lts

Free swap cache entries when swapping in pages if vm_swap_full()
[swap space > 1/2 used?].  Uses new pagevec to reduce pressure
on locks.

Signed-off-by: Rik van Riel <riel@xxxxxxxxxx>
Signed-off-by: Lee Schermerhorn <Lee.Schermerhorn@xxxxxx>

 include/linux/pagevec.h |    1 +
 mm/swap.c               |   18 ++++++++++++++++++
 mm/vmscan.c             |   16 +++++++++++-----
 3 files changed, 30 insertions(+), 5 deletions(-)

Index: linux-2.6.23-rc6-mm1/mm/vmscan.c
===================================================================
--- linux-2.6.23-rc6-mm1.orig/mm/vmscan.c	2007-09-25 15:20:05.000000000 -0400
+++ linux-2.6.23-rc6-mm1/mm/vmscan.c	2007-09-25 15:25:04.000000000 -0400
@@ -613,6 +613,9 @@ free_it:
 		continue;
 
 activate_locked:
+		/* Not a candidate for swapping, so reclaim swap space. */
+		if (PageSwapCache(page) && vm_swap_full())
+			remove_exclusive_swap_page(page);
 		SetPageActive(page);
 		pgactivate++;
 keep_locked:
@@ -1142,14 +1145,13 @@ force_reclaim_mapped:
 		}
 	}
 	__mod_zone_page_state(zone, NR_INACTIVE, pgmoved);
+	spin_unlock_irq(&zone->lru_lock);
 	pgdeactivate += pgmoved;
-	if (buffer_heads_over_limit) {
-		spin_unlock_irq(&zone->lru_lock);
-		pagevec_strip(&pvec);
-		spin_lock_irq(&zone->lru_lock);
-	}
 
+	if (buffer_heads_over_limit)
+		pagevec_strip(&pvec);
 	pgmoved = 0;
+	spin_lock_irq(&zone->lru_lock);
 	while (!list_empty(&l_active)) {
 		page = lru_to_page(&l_active);
 		prefetchw_prev_lru_page(page, &l_active, flags);
@@ -1163,6 +1165,8 @@ force_reclaim_mapped:
 			__mod_zone_page_state(zone, NR_ACTIVE, pgmoved);
 			pgmoved = 0;
 			spin_unlock_irq(&zone->lru_lock);
+			if (vm_swap_full())
+				pagevec_swap_free(&pvec);
 			__pagevec_release(&pvec);
 			spin_lock_irq(&zone->lru_lock);
 		}
@@ -1172,6 +1176,8 @@ force_reclaim_mapped:
 	__count_zone_vm_events(PGREFILL, zone, pgscanned);
 	__count_vm_events(PGDEACTIVATE, pgdeactivate);
 	spin_unlock_irq(&zone->lru_lock);
+	if (vm_swap_full())
+		pagevec_swap_free(&pvec);
 
 	pagevec_release(&pvec);
 }
Index: linux-2.6.23-rc6-mm1/mm/swap.c
===================================================================
--- linux-2.6.23-rc6-mm1.orig/mm/swap.c	2007-09-25 15:20:05.000000000 -0400
+++ linux-2.6.23-rc6-mm1/mm/swap.c	2007-09-25 15:22:51.000000000 -0400
@@ -421,6 +421,24 @@ void pagevec_strip(struct pagevec *pvec)
 	}
 }
 
+/*
+ * Try to free swap space from the pages in a pagevec
+ */
+void pagevec_swap_free(struct pagevec *pvec)
+{
+	int i;
+
+	for (i = 0; i < pagevec_count(pvec); i++) {
+		struct page *page = pvec->pages[i];
+
+		if (PageSwapCache(page) && !TestSetPageLocked(page)) {
+			if (PageSwapCache(page))
+				remove_exclusive_swap_page(page);
+			unlock_page(page);
+		}
+	}
+}
+
 /**
  * pagevec_lookup - gang pagecache lookup
  * @pvec:	Where the resulting pages are placed
Index: linux-2.6.23-rc6-mm1/include/linux/pagevec.h
===================================================================
--- linux-2.6.23-rc6-mm1.orig/include/linux/pagevec.h	2007-09-25 15:20:02.000000000 -0400
+++ linux-2.6.23-rc6-mm1/include/linux/pagevec.h	2007-09-25 15:22:51.000000000 -0400
@@ -26,6 +26,7 @@ void __pagevec_free(struct pagevec *pvec
 void __pagevec_lru_add(struct pagevec *pvec);
 void __pagevec_lru_add_active(struct pagevec *pvec);
 void pagevec_strip(struct pagevec *pvec);
+void pagevec_swap_free(struct pagevec *pvec);
 unsigned pagevec_lookup(struct pagevec *pvec, struct address_space *mapping,
 		pgoff_t start, unsigned nr_pages);
 unsigned pagevec_lookup_tag(struct pagevec *pvec,
-
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