[PATCH] mm: count only reclaimable lru pages v2

[Wu Fengguang]

On Thu, Jul 16, 2009 at 10:42:56PM +0800, Rik van Riel wrote:
> Christoph Lameter wrote:
> > On Thu, 16 Jul 2009, Peter Zijlstra wrote:
> > 
> >>> What would you suggest?  In fact I'm not totally comfortable with it.
> >>> Maybe it would be safer to simply stick with the old _lru_pages
> >>> naming?
> >> Nah, I like the reclaimable name, these pages are at least potentially
> >> reclaimable.
> >>
> >> lru_pages() is definately not correct anymore since you exclude the
> >> unevictable and possibly the anon pages.
> > 
> > Well lets at least add a comment at the beginning of the functions
> > explaining that these are potentially reclaimable and list some of the
> > types of pages that may not be reclaimable.

How about this one?

/*
 * The reclaimable count would be mostly accurate.
 * The less reclaimable pages may be
 * - mlocked pages, which will be moved to unevictable list when encountered
 * - mapped pages, which may require several travels to be reclaimed 
 * - dirty pages, which is not "instantly" reclaimable
 */

> 
> The pages that are not reclaimable will be on the
> unevictable LRU list, not on the lists we count.
> 
> The only case of pages not being evictable is the
> anon pages, once swap fills up.

OK let's settle with the commented {global,zone}_reclaimable_pages.

Thanks,
Fengguang

---
mm: count only reclaimable lru pages 

global_lru_pages() / zone_lru_pages() can be used in two ways:
- to estimate max reclaimable pages in determine_dirtyable_memory()  
- to calculate the slab scan ratio

When swap is full or not present, the anon lru lists are not reclaimable
and also won't be scanned. So the anon pages shall not be counted in both
usage scenarios. Also rename to _reclaimable_pages: now they are counting
the possibly reclaimable lru pages.

It can greatly (and correctly) increase the slab scan rate under high memory
pressure (when most file pages have been reclaimed and swap is full/absent),
thus reduce false OOM kills.

Acked-by: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Reviewed-by: Rik van Riel <riel@xxxxxxxxxx>
Reviewed-by: Christoph Lameter <cl@xxxxxxxxxxxxxxxxxxxx>
Reviewed-by: Minchan Kim <minchan.kim@xxxxxxxxx>
Cc: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>
Signed-off-by: Wu Fengguang <fengguang.wu@xxxxxxxxx>
---
 include/linux/vmstat.h |   11 +-------
 mm/page-writeback.c    |    5 ++-
 mm/vmscan.c            |   50 ++++++++++++++++++++++++++++++---------
 3 files changed, 44 insertions(+), 22 deletions(-)

--- linux.orig/include/linux/vmstat.h
+++ linux/include/linux/vmstat.h
@@ -166,15 +166,8 @@ static inline unsigned long zone_page_st
 	return x;
 }
 
-extern unsigned long global_lru_pages(void);
-
-static inline unsigned long zone_lru_pages(struct zone *zone)
-{
-	return (zone_page_state(zone, NR_ACTIVE_ANON)
-		+ zone_page_state(zone, NR_ACTIVE_FILE)
-		+ zone_page_state(zone, NR_INACTIVE_ANON)
-		+ zone_page_state(zone, NR_INACTIVE_FILE));
-}
+extern unsigned long global_reclaimable_pages(void);
+extern unsigned long zone_reclaimable_pages(struct zone *zone);
 
 #ifdef CONFIG_NUMA
 /*
--- linux.orig/mm/page-writeback.c
+++ linux/mm/page-writeback.c
@@ -380,7 +380,8 @@ static unsigned long highmem_dirtyable_m
 		struct zone *z =
 			&NODE_DATA(node)->node_zones[ZONE_HIGHMEM];
 
-		x += zone_page_state(z, NR_FREE_PAGES) + zone_lru_pages(z);
+		x += zone_page_state(z, NR_FREE_PAGES) +
+		     zone_reclaimable_pages(z);
 	}
 	/*
 	 * Make sure that the number of highmem pages is never larger
@@ -404,7 +405,7 @@ unsigned long determine_dirtyable_memory
 {
 	unsigned long x;
 
-	x = global_page_state(NR_FREE_PAGES) + global_lru_pages();
+	x = global_page_state(NR_FREE_PAGES) + global_reclaimable_pages();
 
 	if (!vm_highmem_is_dirtyable)
 		x -= highmem_dirtyable_memory(x);
--- linux.orig/mm/vmscan.c
+++ linux/mm/vmscan.c
@@ -1735,7 +1735,7 @@ static unsigned long do_try_to_free_page
 			if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
 				continue;
 
-			lru_pages += zone_lru_pages(zone);
+			lru_pages += zone_reclaimable_pages(zone);
 		}
 	}
 
@@ -1952,7 +1952,7 @@ loop_again:
 		for (i = 0; i <= end_zone; i++) {
 			struct zone *zone = pgdat->node_zones + i;
 
-			lru_pages += zone_lru_pages(zone);
+			lru_pages += zone_reclaimable_pages(zone);
 		}
 
 		/*
@@ -1996,7 +1996,7 @@ loop_again:
 			if (zone_is_all_unreclaimable(zone))
 				continue;
 			if (nr_slab == 0 && zone->pages_scanned >=
-						(zone_lru_pages(zone) * 6))
+					(zone_reclaimable_pages(zone) * 6))
 					zone_set_flag(zone,
 						      ZONE_ALL_UNRECLAIMABLE);
 			/*
@@ -2163,12 +2163,39 @@ void wakeup_kswapd(struct zone *zone, in
 	wake_up_interruptible(&pgdat->kswapd_wait);
 }
 
-unsigned long global_lru_pages(void)
+/*
+ * The reclaimable count would be mostly accurate.
+ * The less reclaimable pages may be
+ * - mlocked pages, which will be moved to unevictable list when encountered
+ * - mapped pages, which may require several travels to be reclaimed
+ * - dirty pages, which is not "instantly" reclaimable
+ */
+unsigned long global_reclaimable_pages(void)
 {
-	return global_page_state(NR_ACTIVE_ANON)
-		+ global_page_state(NR_ACTIVE_FILE)
-		+ global_page_state(NR_INACTIVE_ANON)
-		+ global_page_state(NR_INACTIVE_FILE);
+	int nr;
+
+	nr = global_page_state(NR_ACTIVE_FILE) +
+	     global_page_state(NR_INACTIVE_FILE);
+
+	if (nr_swap_pages > 0)
+		nr += global_page_state(NR_ACTIVE_ANON) +
+		      global_page_state(NR_INACTIVE_ANON);
+
+	return nr;
+}
+
+unsigned long zone_reclaimable_pages(struct zone *zone)
+{
+	int nr;
+
+	nr = zone_page_state(zone, NR_ACTIVE_FILE) +
+	     zone_page_state(zone, NR_INACTIVE_FILE);
+
+	if (nr_swap_pages > 0)
+		nr += zone_page_state(zone, NR_ACTIVE_ANON) +
+		      zone_page_state(zone, NR_INACTIVE_ANON);
+
+	return nr;
 }
 
 #ifdef CONFIG_HIBERNATION
@@ -2240,7 +2267,7 @@ unsigned long shrink_all_memory(unsigned
 
 	current->reclaim_state = &reclaim_state;
 
-	lru_pages = global_lru_pages();
+	lru_pages = global_reclaimable_pages();
 	nr_slab = global_page_state(NR_SLAB_RECLAIMABLE);
 	/* If slab caches are huge, it's better to hit them first */
 	while (nr_slab >= lru_pages) {
@@ -2282,7 +2309,7 @@ unsigned long shrink_all_memory(unsigned
 
 			reclaim_state.reclaimed_slab = 0;
 			shrink_slab(sc.nr_scanned, sc.gfp_mask,
-					global_lru_pages());
+				    global_reclaimable_pages());
 			sc.nr_reclaimed += reclaim_state.reclaimed_slab;
 			if (sc.nr_reclaimed >= nr_pages)
 				goto out;
@@ -2299,7 +2326,8 @@ unsigned long shrink_all_memory(unsigned
 	if (!sc.nr_reclaimed) {
 		do {
 			reclaim_state.reclaimed_slab = 0;
-			shrink_slab(nr_pages, sc.gfp_mask, global_lru_pages());
+			shrink_slab(nr_pages, sc.gfp_mask,
+				    global_reclaimable_pages());
 			sc.nr_reclaimed += reclaim_state.reclaimed_slab;
 		} while (sc.nr_reclaimed < nr_pages &&
 				reclaim_state.reclaimed_slab > 0);
--
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