[patch 0/2] vmscan: one cleanup, one bugfix

[patch 0/2] vmscan: one cleanup, one bugfix

[Johannes Weiner]

Hi Andrew,

the first patch is from KOSAKI Motohiro, it moves the suspend-to-disk memory
shrinking functions to use sc.nr_reclaimed all over instead of maintaining
an extra local variable.

The second patch is a bugfix for shrink_all_memory() which currently does
reclaim more than requested because of setting swap_cluster_max once to our
overall reclaim goal but failing to decrease it while we go and reclaim is
making progress.  Added Nigel Cunningham to Cc because ISTR he complained
about exactly this behaviour.  Well, this patch seems to fix it, I even
added some shiny numbers coming from real tests!

	Hannes

 mm/vmscan.c |   51 ++++++++++++++++++++++++---------------------------
 1 files changed, 24 insertions(+), 27 deletions(-)

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[patch 1/2] shrink_all_memory(): use sc.nr_reclaimed

[Johannes Weiner]

[-- Attachment #1: shrink_all_memory-use-sc.nr_reclaimed.patch --]
[-- Type: text/plain, Size: 4254 bytes --]

Impact: cleanup

Commit a79311c14eae4bb946a97af25f3e1b17d625985d "vmscan: bail out of
direct reclaim after swap_cluster_max pages" moved the nr_reclaimed
counter into the scan control to accumulate the number of all
reclaimed pages in a reclaim invocation.

shrink_all_memory() can use the same mechanism. it increase code 
consistency.

Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: MinChan Kim <minchan.kim@gmail.com>
Cc: "Rafael J. Wysocki" <rjw@sisk.pl>
Cc: Rik van Riel <riel@redhat.com>
---
 mm/vmscan.c |   49 +++++++++++++++++++++++--------------------------
 1 file changed, 23 insertions(+), 26 deletions(-)

--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2048,16 +2048,14 @@ unsigned long global_lru_pages(void)
 #ifdef CONFIG_PM
 /*
  * Helper function for shrink_all_memory().  Tries to reclaim 'nr_pages' pages
- * from LRU lists system-wide, for given pass and priority, and returns the
- * number of reclaimed pages
+ * from LRU lists system-wide, for given pass and priority.
  *
  * For pass > 3 we also try to shrink the LRU lists that contain a few pages
  */
-static unsigned long shrink_all_zones(unsigned long nr_pages, int prio,
-				      int pass, struct scan_control *sc)
+static void shrink_all_zones(unsigned long nr_pages, int prio,
+			      int pass, struct scan_control *sc)
 {
 	struct zone *zone;
-	unsigned long ret = 0;
 
 	for_each_zone(zone) {
 		enum lru_list l;
@@ -2082,14 +2080,13 @@ static unsigned long shrink_all_zones(un
 
 				zone->lru[l].nr_scan = 0;
 				nr_to_scan = min(nr_pages, lru_pages);
-				ret += shrink_list(l, nr_to_scan, zone,
-								sc, prio);
-				if (ret >= nr_pages)
-					return ret;
+				sc->nr_reclaimed += shrink_list(l, nr_to_scan,
+								zone, sc, prio);
+				if (sc->nr_reclaimed >= nr_pages)
+					return;
 			}
 		}
 	}
-	return ret;
 }
 
 /*
@@ -2103,7 +2100,6 @@ static unsigned long shrink_all_zones(un
 unsigned long shrink_all_memory(unsigned long nr_pages)
 {
 	unsigned long lru_pages, nr_slab;
-	unsigned long ret = 0;
 	int pass;
 	struct reclaim_state reclaim_state;
 	struct scan_control sc = {
@@ -2125,8 +2121,8 @@ unsigned long shrink_all_memory(unsigned
 		if (!reclaim_state.reclaimed_slab)
 			break;
 
-		ret += reclaim_state.reclaimed_slab;
-		if (ret >= nr_pages)
+		sc.nr_reclaimed += reclaim_state.reclaimed_slab;
+		if (sc.nr_reclaimed >= nr_pages)
 			goto out;
 
 		nr_slab -= reclaim_state.reclaimed_slab;
@@ -2148,18 +2144,18 @@ unsigned long shrink_all_memory(unsigned
 			sc.may_unmap = 1;
 
 		for (prio = DEF_PRIORITY; prio >= 0; prio--) {
-			unsigned long nr_to_scan = nr_pages - ret;
+			unsigned long nr_to_scan = nr_pages - sc.nr_reclaimed;
 
 			sc.nr_scanned = 0;
-			ret += shrink_all_zones(nr_to_scan, prio, pass, &sc);
-			if (ret >= nr_pages)
+			shrink_all_zones(nr_to_scan, prio, pass, &sc);
+			if (sc.nr_reclaimed >= nr_pages)
 				goto out;
 
 			reclaim_state.reclaimed_slab = 0;
 			shrink_slab(sc.nr_scanned, sc.gfp_mask,
 					global_lru_pages());
-			ret += reclaim_state.reclaimed_slab;
-			if (ret >= nr_pages)
+			sc.nr_reclaimed += reclaim_state.reclaimed_slab;
+			if (sc.nr_reclaimed >= nr_pages)
 				goto out;
 
 			if (sc.nr_scanned && prio < DEF_PRIORITY - 2)
@@ -2167,22 +2163,23 @@ unsigned long shrink_all_memory(unsigned
 		}
 	}
 
-	/*
-	 * If ret = 0, we could not shrink LRUs, but there may be something
-	 * in slab caches
-	 */
-	if (!ret) {
+	if (!sc.nr_reclaimed) {
+		/*
+		 * We could not shrink LRUs, but there may be something
+		 * in slab caches.
+		 */
 		do {
 			reclaim_state.reclaimed_slab = 0;
 			shrink_slab(nr_pages, sc.gfp_mask, global_lru_pages());
-			ret += reclaim_state.reclaimed_slab;
-		} while (ret < nr_pages && reclaim_state.reclaimed_slab > 0);
+			sc.nr_reclaimed += reclaim_state.reclaimed_slab;
+		} while (sc.nr_reclaimed < nr_pages &&
+				reclaim_state.reclaimed_slab > 0);
 	}
 
 out:
 	current->reclaim_state = NULL;
 
-	return ret;
+	return sc.nr_reclaimed;
 }
 #endif
 


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[patch 2/2] vmscan: clip swap_cluster_max in shrink_all_memory()

[Johannes Weiner]

[-- Attachment #1: vmscan-clip-swap_cluster_max-in-shrink_all_memory.patch --]
[-- Type: text/plain, Size: 2928 bytes --]

shrink_inactive_list() scans in sc->swap_cluster_max chunks until it
hits the scan limit it was passed.

shrink_inactive_list()
{
	do {
		isolate_pages(swap_cluster_max)
		shrink_page_list()
	} while (nr_scanned < max_scan);
}

This assumes that swap_cluster_max is not bigger than the scan limit
because the latter is checked only after at least one iteration.

In shrink_all_memory() sc->swap_cluster_max is initialized to the
overall reclaim goal in the beginning but not decreased while reclaim
is making progress which leads to subsequent calls to
shrink_inactive_list() reclaiming way too much in the one iteration
that is done unconditionally.

Set sc->swap_cluster_max always to the proper goal before doing
  shrink_all_zones()
    shrink_list()
      shrink_inactive_list().

While the current shrink_all_memory() happily reclaims more than
actually requested, this patch fixes it to never exceed the goal:

unpatched
   wanted=10000 reclaimed=13356
   wanted=10000 reclaimed=19711
   wanted=10000 reclaimed=10289
   wanted=10000 reclaimed=17306
   wanted=10000 reclaimed=10700
   wanted=10000 reclaimed=10004
   wanted=10000 reclaimed=13301
   wanted=10000 reclaimed=10976
   wanted=10000 reclaimed=10605
   wanted=10000 reclaimed=10088
   wanted=10000 reclaimed=15000

patched
   wanted=10000 reclaimed=10000
   wanted=10000 reclaimed=9599
   wanted=10000 reclaimed=8476
   wanted=10000 reclaimed=8326
   wanted=10000 reclaimed=10000
   wanted=10000 reclaimed=10000
   wanted=10000 reclaimed=9919
   wanted=10000 reclaimed=10000
   wanted=10000 reclaimed=10000
   wanted=10000 reclaimed=10000
   wanted=10000 reclaimed=10000
   wanted=10000 reclaimed=9624
   wanted=10000 reclaimed=10000
   wanted=10000 reclaimed=10000
   wanted=8500 reclaimed=8092
   wanted=316 reclaimed=316

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: MinChan Kim <minchan.kim@gmail.com>
Cc: "Rafael J. Wysocki" <rjw@sisk.pl>
Cc: Nigel Cunningham <ncunningham-lkml@crca.org.au>
Cc: Rik van Riel <riel@redhat.com>
---
 mm/vmscan.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2105,7 +2105,6 @@ unsigned long shrink_all_memory(unsigned
 	struct scan_control sc = {
 		.gfp_mask = GFP_KERNEL,
 		.may_unmap = 0,
-		.swap_cluster_max = nr_pages,
 		.may_writepage = 1,
 		.isolate_pages = isolate_pages_global,
 	};
@@ -2147,6 +2146,7 @@ unsigned long shrink_all_memory(unsigned
 			unsigned long nr_to_scan = nr_pages - sc.nr_reclaimed;
 
 			sc.nr_scanned = 0;
+			sc.swap_cluster_max = nr_to_scan;
 			shrink_all_zones(nr_to_scan, prio, pass, &sc);
 			if (sc.nr_reclaimed >= nr_pages)
 				goto out;


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