[PATCH] tty: Take a 256 byte padding into account when buffering below sub-page units

[Mel Gorman]

The TTY layer takes some care to ensure that only sub-page allocations
are made with interrupts disabled. It does this by setting a goal of
"TTY_BUFFER_PAGE" to allocate. Unfortunately, while TTY_BUFFER_PAGE takes the
size of tty_buffer into account, it fails to account that tty_buffer_find()
rounds the buffer size out to the next 256 byte boundary before adding on
the size of the tty_buffer.

This patch adjusts the TTY_BUFFER_PAGE calculation to take into account the
size of the tty_buffer and the padding. Once applied, tty_buffer_alloc()
should not require high-order allocations.

Signed-off-by: Mel Gorman <mel@xxxxxxxxx>
Cc: stable <stable@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxx>

diff --git a/include/linux/tty.h b/include/linux/tty.h
index 568369a..593228a 100644
--- a/include/linux/tty.h
+++ b/include/linux/tty.h
@@ -70,12 +70,13 @@ struct tty_buffer {
 
 /*
  * We default to dicing tty buffer allocations to this many characters
- * in order to avoid multiple page allocations. We assume tty_buffer itself
- * is under 256 bytes. See tty_buffer_find for the allocation logic this
- * must match
+ * in order to avoid multiple page allocations. We know the size of
+ * tty_buffer itself but it must also be taken into account that the
+ * the buffer is 256 byte aligned. See tty_buffer_find for the allocation
+ * logic this must match
  */
 
-#define TTY_BUFFER_PAGE		((PAGE_SIZE  - 256) / 2)
+#define TTY_BUFFER_PAGE	(((PAGE_SIZE - sizeof(struct tty_buffer)) / 2) & ~0xFF)
 
 
 struct tty_bufhead {
diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index bf9213b..5ba0d9a 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -94,7 +94,6 @@ extern void mem_cgroup_note_reclaim_priority(struct mem_cgroup *mem,
 extern void mem_cgroup_record_reclaim_priority(struct mem_cgroup *mem,
 							int priority);
 int mem_cgroup_inactive_anon_is_low(struct mem_cgroup *memcg);
-int mem_cgroup_inactive_file_is_low(struct mem_cgroup *memcg);
 unsigned long mem_cgroup_zone_nr_pages(struct mem_cgroup *memcg,
 				       struct zone *zone,
 				       enum lru_list lru);
@@ -243,12 +242,6 @@ mem_cgroup_inactive_anon_is_low(struct mem_cgroup *memcg)
 	return 1;
 }
 
-static inline int
-mem_cgroup_inactive_file_is_low(struct mem_cgroup *memcg)
-{
-	return 1;
-}
-
 static inline unsigned long
 mem_cgroup_zone_nr_pages(struct mem_cgroup *memcg, struct zone *zone,
 			 enum lru_list lru)
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 66035bf..bbb0eda 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -843,17 +843,6 @@ int mem_cgroup_inactive_anon_is_low(struct mem_cgroup *memcg)
 	return 0;
 }
 
-int mem_cgroup_inactive_file_is_low(struct mem_cgroup *memcg)
-{
-	unsigned long active;
-	unsigned long inactive;
-
-	inactive = mem_cgroup_get_local_zonestat(memcg, LRU_INACTIVE_FILE);
-	active = mem_cgroup_get_local_zonestat(memcg, LRU_ACTIVE_FILE);
-
-	return (active > inactive);
-}
-
 unsigned long mem_cgroup_zone_nr_pages(struct mem_cgroup *memcg,
 				       struct zone *zone,
 				       enum lru_list lru)
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 692807f..5512301 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1428,59 +1428,13 @@ static int inactive_anon_is_low(struct zone *zone, struct scan_control *sc)
 	return low;
 }
 
-static int inactive_file_is_low_global(struct zone *zone)
-{
-	unsigned long active, inactive;
-
-	active = zone_page_state(zone, NR_ACTIVE_FILE);
-	inactive = zone_page_state(zone, NR_INACTIVE_FILE);
-
-	return (active > inactive);
-}
-
-/**
- * inactive_file_is_low - check if file pages need to be deactivated
- * @zone: zone to check
- * @sc:   scan control of this context
- *
- * When the system is doing streaming IO, memory pressure here
- * ensures that active file pages get deactivated, until more
- * than half of the file pages are on the inactive list.
- *
- * Once we get to that situation, protect the system's working
- * set from being evicted by disabling active file page aging.
- *
- * This uses a different ratio than the anonymous pages, because
- * the page cache uses a use-once replacement algorithm.
- */
-static int inactive_file_is_low(struct zone *zone, struct scan_control *sc)
-{
-	int low;
-
-	if (scanning_global_lru(sc))
-		low = inactive_file_is_low_global(zone);
-	else
-		low = mem_cgroup_inactive_file_is_low(sc->mem_cgroup);
-	return low;
-}
-
-static int inactive_list_is_low(struct zone *zone, struct scan_control *sc,
-				int file)
-{
-	if (file)
-		return inactive_file_is_low(zone, sc);
-	else
-		return inactive_anon_is_low(zone, sc);
-}
-
 static unsigned long shrink_list(enum lru_list lru, unsigned long nr_to_scan,
 	struct zone *zone, struct scan_control *sc, int priority)
 {
 	int file = is_file_lru(lru);
 
-	if (is_active_lru(lru)) {
-		if (inactive_list_is_low(zone, sc, file))
-		    shrink_active_list(nr_to_scan, zone, sc, priority, file);
+	if (lru == LRU_ACTIVE_FILE) {
+		shrink_active_list(nr_to_scan, zone, sc, priority, file);
 		return 0;
 	}
 

-- 
Mel Gorman
Part-time Phd Student                          Linux Technology Center
University of Limerick                         IBM Dublin Software Lab
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