Make release_pages(), __pagevec_lru_add() and __pagevec_lru_active() preserve irq status

The swap migration code calls drain_lru_pages() to be able to push pages off the
LRU in order to cleanly remove a page from the LRU. It uses smp_call_function()
for this purpose which uses IPIs to notify other processors. On IA64 IPIs are
processes with enabled interrupts. However, other architectures
keep the interrupts disabled during IPI processing.

This patch makes the functions called in mm/swap.c preserve the interrupt
state so that it is safe to call drain_lru_pages() during IPI on all platforms.

The preservation of the interrupt state may allow the functions to be used in other
contexts in the future.

Signed-off-by: Christoph Lameter <clameter@sgi.com>

Index: linux-2.6.14-mm2/mm/swap.c
===================================================================
--- linux-2.6.14-mm2.orig/mm/swap.c	2005-11-15 10:29:53.000000000 -0800
+++ linux-2.6.14-mm2/mm/swap.c	2005-11-16 16:05:07.000000000 -0800
@@ -102,15 +102,16 @@ int rotate_reclaimable_page(struct page 
 void fastcall activate_page(struct page *page)
 {
 	struct zone *zone = page_zone(page);
+	unsigned long flags;
 
-	spin_lock_irq(&zone->lru_lock);
+	spin_lock_irqsave(&zone->lru_lock, flags);
 	if (PageLRU(page) && !PageActive(page)) {
 		del_page_from_inactive_list(zone, page);
 		SetPageActive(page);
 		add_page_to_active_list(zone, page);
 		inc_page_state(pgactivate);
 	}
-	spin_unlock_irq(&zone->lru_lock);
+	spin_unlock_irqrestore(&zone->lru_lock, flags);
 }
 
 /*
@@ -209,6 +210,7 @@ void release_pages(struct page **pages, 
 	int i;
 	struct pagevec pages_to_free;
 	struct zone *zone = NULL;
+	unsigned long flags = 0;	/* GCC warning */
 
 	pagevec_init(&pages_to_free, cold);
 	for (i = 0; i < nr; i++) {
@@ -221,15 +223,15 @@ void release_pages(struct page **pages, 
 		pagezone = page_zone(page);
 		if (pagezone != zone) {
 			if (zone)
-				spin_unlock_irq(&zone->lru_lock);
+				spin_unlock_irqrestore(&zone->lru_lock, flags);
 			zone = pagezone;
-			spin_lock_irq(&zone->lru_lock);
+			spin_lock_irqsave(&zone->lru_lock, flags);
 		}
 		if (TestClearPageLRU(page))
 			del_page_from_lru(zone, page);
 		if (page_count(page) == 0) {
 			if (!pagevec_add(&pages_to_free, page)) {
-				spin_unlock_irq(&zone->lru_lock);
+				spin_unlock_irqrestore(&zone->lru_lock, flags);
 				__pagevec_free(&pages_to_free);
 				pagevec_reinit(&pages_to_free);
 				zone = NULL;	/* No lock is held */
@@ -237,7 +239,7 @@ void release_pages(struct page **pages, 
 		}
 	}
 	if (zone)
-		spin_unlock_irq(&zone->lru_lock);
+		spin_unlock_irqrestore(&zone->lru_lock, flags);
 
 	pagevec_free(&pages_to_free);
 }
@@ -291,6 +293,7 @@ void __pagevec_lru_add(struct pagevec *p
 {
 	int i;
 	struct zone *zone = NULL;
+	unsigned long flags = 0;	/* GCC warning */
 
 	for (i = 0; i < pagevec_count(pvec); i++) {
 		struct page *page = pvec->pages[i];
@@ -298,16 +301,16 @@ void __pagevec_lru_add(struct pagevec *p
 
 		if (pagezone != zone) {
 			if (zone)
-				spin_unlock_irq(&zone->lru_lock);
+				spin_unlock_irqrestore(&zone->lru_lock, flags);
 			zone = pagezone;
-			spin_lock_irq(&zone->lru_lock);
+			spin_lock_irqsave(&zone->lru_lock, flags);
 		}
 		if (TestSetPageLRU(page))
 			BUG();
 		add_page_to_inactive_list(zone, page);
 	}
 	if (zone)
-		spin_unlock_irq(&zone->lru_lock);
+		spin_unlock_irqrestore(&zone->lru_lock, flags);
 	release_pages(pvec->pages, pvec->nr, pvec->cold);
 	pagevec_reinit(pvec);
 }
@@ -318,6 +321,7 @@ void __pagevec_lru_add_active(struct pag
 {
 	int i;
 	struct zone *zone = NULL;
+	unsigned long flags = 0;	/* GCC warning */
 
 	for (i = 0; i < pagevec_count(pvec); i++) {
 		struct page *page = pvec->pages[i];
@@ -325,9 +329,9 @@ void __pagevec_lru_add_active(struct pag
 
 		if (pagezone != zone) {
 			if (zone)
-				spin_unlock_irq(&zone->lru_lock);
+				spin_unlock_irqrestore(&zone->lru_lock, flags);
 			zone = pagezone;
-			spin_lock_irq(&zone->lru_lock);
+			spin_lock_irqsave(&zone->lru_lock, flags);
 		}
 		if (TestSetPageLRU(page))
 			BUG();
@@ -336,7 +340,7 @@ void __pagevec_lru_add_active(struct pag
 		add_page_to_active_list(zone, page);
 	}
 	if (zone)
-		spin_unlock_irq(&zone->lru_lock);
+		spin_unlock_irqrestore(&zone->lru_lock, flags);
 	release_pages(pvec->pages, pvec->nr, pvec->cold);
 	pagevec_reinit(pvec);
 }