[RESEND PATCH v2] mm/vmscan.c: wrap five parameters into writeback_stats for reducing the stack consumption

[Chen Yucong <slaoub@gmail.com>]

shrink_page_list() has too many arguments that have already reached ten.
Some of those arguments and temporary variables introduces extra 80 bytes
on the stack. This patch wraps five parameters into writeback_stats and removes
some temporary variables, thus making the relative functions to consume fewer
stack space.

Before mm/vmscan.c is changed:
   text    data     bss     dec     hex filename
6876698  957224  966656 8800578  864942 vmlinux-3.15

After mm/vmscan.c is changed:
   text    data     bss     dec     hex filename
6876506  957224  966656 8800386  864882 vmlinux-3.15


scripts/checkstack.pl can be used for checking the change of the target function stack.

Before mm/vmscan.c is changed:

0xffffffff810af103 shrink_inactive_list []:		152
0xffffffff810af43d shrink_inactive_list []:		152
-------------------------------------------------------------
0xffffffff810aede8 reclaim_clean_pages_from_list []:	184
0xffffffff810aeef8 reclaim_clean_pages_from_list []:	184
-------------------------------------------------------------
0xffffffff810ae582 shrink_page_list []:			232
0xffffffff810aedb5 shrink_page_list []:			232

After mm/vmscan.c is changed::

0xffffffff810af078 shrink_inactive_list []:		120
0xffffffff810af36d shrink_inactive_list []:		120
-------------------------------------------------------------
With: struct writeback_stats dummy = {};
0xffffffff810aed6c reclaim_clean_pages_from_list []:    152
0xffffffff810aee68 reclaim_clean_pages_from_list []:    152
-------------------------------------------------------------
With: static struct writeback_stats dummy ={};
0xffffffff810aed69 reclaim_clean_pages_from_list []:    120
0xffffffff810aee4d reclaim_clean_pages_from_list []:    120
--------------------------------------------------------------------------------------
0xffffffff810ae586 shrink_page_list []:			184   ---> sub    $0xb8,%rsp
0xffffffff810aed36 shrink_page_list []:			184   ---> add    $0xb8,%rsp

Via the above figures, we can find that the difference value of the stack is 32 for
shrink_inactive_list and reclaim_clean_pages_from_list, and this value is 48(232-184)
for shrink_page_list. From the hierarchy of functions called, the total difference
value is 80(32+48) for this change.

Changes since v1: https://lkml.org/lkml/2014/6/12/159
     * Rename arg_container to writeback_stats
     * Change the the way of initializing writeback_stats object.

Signed-off-by: Chen Yucong <slaoub@gmail.com>
---
 mm/vmscan.c |   62 ++++++++++++++++++++++++++---------------------------------
 1 file changed, 27 insertions(+), 35 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index a8ffe4e..3f28e39 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -791,28 +791,31 @@ static void page_check_dirty_writeback(struct page *page,
 }
 
 /*
+ * Callers pass a prezeroed writeback_stats into the shrink functions to gather
+ * statistics about how many pages of particular states were processed
+ */
+struct writeback_stats {
+	unsigned long nr_dirty;
+	unsigned long nr_unqueued_dirty;
+	unsigned long nr_congested;
+	unsigned long nr_writeback;
+	unsigned long nr_immediate;
+};
+
+/*
  * shrink_page_list() returns the number of reclaimed pages
  */
 static unsigned long shrink_page_list(struct list_head *page_list,
 				      struct zone *zone,
 				      struct scan_control *sc,
 				      enum ttu_flags ttu_flags,
-				      unsigned long *ret_nr_dirty,
-				      unsigned long *ret_nr_unqueued_dirty,
-				      unsigned long *ret_nr_congested,
-				      unsigned long *ret_nr_writeback,
-				      unsigned long *ret_nr_immediate,
+				      struct writeback_stats *ws,
 				      bool force_reclaim)
 {
 	LIST_HEAD(ret_pages);
 	LIST_HEAD(free_pages);
 	int pgactivate = 0;
-	unsigned long nr_unqueued_dirty = 0;
-	unsigned long nr_dirty = 0;
-	unsigned long nr_congested = 0;
 	unsigned long nr_reclaimed = 0;
-	unsigned long nr_writeback = 0;
-	unsigned long nr_immediate = 0;
 
 	cond_resched();
 
@@ -858,10 +861,10 @@ static unsigned long shrink_page_list(struct list_head *page_list,
 		 */
 		page_check_dirty_writeback(page, &dirty, &writeback);
 		if (dirty || writeback)
-			nr_dirty++;
+			ws->nr_dirty++;
 
 		if (dirty && !writeback)
-			nr_unqueued_dirty++;
+			ws->nr_unqueued_dirty++;
 
 		/*
 		 * Treat this page as congested if the underlying BDI is or if
@@ -872,7 +875,7 @@ static unsigned long shrink_page_list(struct list_head *page_list,
 		mapping = page_mapping(page);
 		if ((mapping && bdi_write_congested(mapping->backing_dev_info)) ||
 		    (writeback && PageReclaim(page)))
-			nr_congested++;
+			ws->nr_congested++;
 
 		/*
 		 * If a page at the tail of the LRU is under writeback, there
@@ -916,7 +919,7 @@ static unsigned long shrink_page_list(struct list_head *page_list,
 			if (current_is_kswapd() &&
 			    PageReclaim(page) &&
 			    zone_is_reclaim_writeback(zone)) {
-				nr_immediate++;
+				ws->nr_immediate++;
 				goto keep_locked;
 
 			/* Case 2 above */
@@ -934,7 +937,7 @@ static unsigned long shrink_page_list(struct list_head *page_list,
 				 * and it's also appropriate in global reclaim.
 				 */
 				SetPageReclaim(page);
-				nr_writeback++;
+				ws->nr_writeback++;
 
 				goto keep_locked;
 
@@ -1132,11 +1135,6 @@ keep:
 	list_splice(&ret_pages, page_list);
 	count_vm_events(PGACTIVATE, pgactivate);
 	mem_cgroup_uncharge_end();
-	*ret_nr_dirty += nr_dirty;
-	*ret_nr_congested += nr_congested;
-	*ret_nr_unqueued_dirty += nr_unqueued_dirty;
-	*ret_nr_writeback += nr_writeback;
-	*ret_nr_immediate += nr_immediate;
 	return nr_reclaimed;
 }
 
@@ -1148,7 +1146,8 @@ unsigned long reclaim_clean_pages_from_list(struct zone *zone,
 		.priority = DEF_PRIORITY,
 		.may_unmap = 1,
 	};
-	unsigned long ret, dummy1, dummy2, dummy3, dummy4, dummy5;
+	unsigned long ret;
+	static struct writeback_stats dummy = { };
 	struct page *page, *next;
 	LIST_HEAD(clean_pages);
 
@@ -1161,8 +1160,7 @@ unsigned long reclaim_clean_pages_from_list(struct zone *zone,
 	}
 
 	ret = shrink_page_list(&clean_pages, zone, &sc,
-			TTU_UNMAP|TTU_IGNORE_ACCESS,
-			&dummy1, &dummy2, &dummy3, &dummy4, &dummy5, true);
+			TTU_UNMAP|TTU_IGNORE_ACCESS, &dummy, true);
 	list_splice(&clean_pages, page_list);
 	mod_zone_page_state(zone, NR_ISOLATED_FILE, -ret);
 	return ret;
@@ -1469,11 +1467,7 @@ shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec,
 	unsigned long nr_scanned;
 	unsigned long nr_reclaimed = 0;
 	unsigned long nr_taken;
-	unsigned long nr_dirty = 0;
-	unsigned long nr_congested = 0;
-	unsigned long nr_unqueued_dirty = 0;
-	unsigned long nr_writeback = 0;
-	unsigned long nr_immediate = 0;
+	struct writeback_stats ws = { };
 	isolate_mode_t isolate_mode = 0;
 	int file = is_file_lru(lru);
 	struct zone *zone = lruvec_zone(lruvec);
@@ -1515,9 +1509,7 @@ shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec,
 		return 0;
 
 	nr_reclaimed = shrink_page_list(&page_list, zone, sc, TTU_UNMAP,
-				&nr_dirty, &nr_unqueued_dirty, &nr_congested,
-				&nr_writeback, &nr_immediate,
-				false);
+					&ws, false);
 
 	spin_lock_irq(&zone->lru_lock);
 
@@ -1554,7 +1546,7 @@ shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec,
 	 * of pages under pages flagged for immediate reclaim and stall if any
 	 * are encountered in the nr_immediate check below.
 	 */
-	if (nr_writeback && nr_writeback == nr_taken)
+	if (ws.nr_writeback && ws.nr_writeback == nr_taken)
 		zone_set_flag(zone, ZONE_WRITEBACK);
 
 	/*
@@ -1566,7 +1558,7 @@ shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec,
 		 * Tag a zone as congested if all the dirty pages scanned were
 		 * backed by a congested BDI and wait_iff_congested will stall.
 		 */
-		if (nr_dirty && nr_dirty == nr_congested)
+		if (ws.nr_dirty && ws.nr_dirty == ws.nr_congested)
 			zone_set_flag(zone, ZONE_CONGESTED);
 
 		/*
@@ -1576,7 +1568,7 @@ shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec,
 		 * pages from reclaim context. It will forcibly stall in the
 		 * next check.
 		 */
-		if (nr_unqueued_dirty == nr_taken)
+		if (ws.nr_unqueued_dirty == nr_taken)
 			zone_set_flag(zone, ZONE_TAIL_LRU_DIRTY);
 
 		/*
@@ -1585,7 +1577,7 @@ shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec,
 		 * implies that pages are cycling through the LRU faster than
 		 * they are written so also forcibly stall.
 		 */
-		if ((nr_unqueued_dirty == nr_taken || nr_immediate) &&
+		if ((ws.nr_unqueued_dirty == nr_taken || ws.nr_immediate) &&
 		    current_may_throttle())
 			congestion_wait(BLK_RW_ASYNC, HZ/10);
 	}
-- 
1.7.10.4

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