Re: [PATCH v2] mm: exclude isolated non-lru pages from NR_ISOLATED_ANON or NR_ISOLATED_FILE.

[Michal Hocko]

On Sat 15-10-16 00:26:33, Minchan Kim wrote:
> On Fri, Oct 14, 2016 at 05:03:55PM +0200, Michal Hocko wrote:
[...]
> > diff --git a/mm/compaction.c b/mm/compaction.c
> > index 0409a4ad6ea1..6584705a46f6 100644
> > --- a/mm/compaction.c
> > +++ b/mm/compaction.c
> > @@ -685,7 +685,8 @@ static bool too_many_isolated(struct zone *zone)
> >   */
> >  static unsigned long
> >  isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
> > -			unsigned long end_pfn, isolate_mode_t isolate_mode)
> > +			unsigned long end_pfn, isolate_mode_t isolate_mode,
> > +			unsigned long *isolated_file, unsigned long *isolated_anon)
> >  {
> >  	struct zone *zone = cc->zone;
> >  	unsigned long nr_scanned = 0, nr_isolated = 0;
> > @@ -866,6 +867,10 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
> >  
> >  		/* Successfully isolated */
> >  		del_page_from_lru_list(page, lruvec, page_lru(page));
> > +		if (page_is_file_cache(page))
> > +			(*isolated_file)++;
> > +		else
> > +			(*isolated_anon)++;
> >  
> >  isolate_success:
> >  		list_add(&page->lru, &cc->migratepages);
> > 
> > Makes more sense?
> 
> It is doable for isolation part. IOW, maybe we can make acct_isolated
> simple with those counters but we need to handle migrate, putback part.
> If you want to remove the check of __PageMoable with those counter, it
> means we should pass the counter on every functions related migration
> where isolate, migrate, putback parts.

OK, I see. Can we just get rid of acct_isolated altogether? Why cannot
we simply update NR_ISOLATED_* while isolating pages? Just looking at
isolate_migratepages_block:
			acct_isolated(zone, cc);
			putback_movable_pages(&cc->migratepages);

suggests we are doing something suboptimal. I guess we cannot get rid of
__PageMoveble checks which is sad because that just adds a lot of
confusion because checking for !__PageMovable(page) for LRU pages is
just a head scratcher (LRU pages are movable arent' they?). Maybe it
would be even good to get rid of this misnomer. PageNonLRUMovable?

Anyway, I would suggest to do something like this. Batching NR_ISOLATED*
just doesn't make all that much sense as these are per-cpu and the
resulting code seems to be easier without it.
---
diff --git a/mm/compaction.c b/mm/compaction.c
index 0409a4ad6ea1..df1fd0c20e5c 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -634,22 +634,6 @@ isolate_freepages_range(struct compact_control *cc,
 	return pfn;
 }
 
-/* Update the number of anon and file isolated pages in the zone */
-static void acct_isolated(struct zone *zone, struct compact_control *cc)
-{
-	struct page *page;
-	unsigned int count[2] = { 0, };
-
-	if (list_empty(&cc->migratepages))
-		return;
-
-	list_for_each_entry(page, &cc->migratepages, lru)
-		count[!!page_is_file_cache(page)]++;
-
-	mod_node_page_state(zone->zone_pgdat, NR_ISOLATED_ANON, count[0]);
-	mod_node_page_state(zone->zone_pgdat, NR_ISOLATED_FILE, count[1]);
-}
-
 /* Similar to reclaim, but different enough that they don't share logic */
 static bool too_many_isolated(struct zone *zone)
 {
@@ -866,6 +850,8 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
 
 		/* Successfully isolated */
 		del_page_from_lru_list(page, lruvec, page_lru(page));
+		inc_node_page_state(zone->zone_pgdat,
+				NR_ISOLATED_ANON + page_is_file_cache(page));
 
 isolate_success:
 		list_add(&page->lru, &cc->migratepages);
@@ -902,7 +888,6 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
 				spin_unlock_irqrestore(zone_lru_lock(zone), flags);
 				locked = false;
 			}
-			acct_isolated(zone, cc);
 			putback_movable_pages(&cc->migratepages);
 			cc->nr_migratepages = 0;
 			cc->last_migrated_pfn = 0;
@@ -988,7 +973,6 @@ isolate_migratepages_range(struct compact_control *cc, unsigned long start_pfn,
 		if (cc->nr_migratepages == COMPACT_CLUSTER_MAX)
 			break;
 	}
-	acct_isolated(cc->zone, cc);
 
 	return pfn;
 }
@@ -1258,10 +1242,8 @@ static isolate_migrate_t isolate_migratepages(struct zone *zone,
 		low_pfn = isolate_migratepages_block(cc, low_pfn,
 						block_end_pfn, isolate_mode);
 
-		if (!low_pfn || cc->contended) {
-			acct_isolated(zone, cc);
+		if (!low_pfn || cc->contended)
 			return ISOLATE_ABORT;
-		}
 
 		/*
 		 * Either we isolated something and proceed with migration. Or
@@ -1271,7 +1253,6 @@ static isolate_migrate_t isolate_migratepages(struct zone *zone,
 		break;
 	}
 
-	acct_isolated(zone, cc);
 	/* Record where migration scanner will be restarted. */
 	cc->migrate_pfn = low_pfn;
 
diff --git a/mm/migrate.c b/mm/migrate.c
index 99250aee1ac1..66ce6b490b13 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -168,8 +168,6 @@ void putback_movable_pages(struct list_head *l)
 			continue;
 		}
 		list_del(&page->lru);
-		dec_node_page_state(page, NR_ISOLATED_ANON +
-				page_is_file_cache(page));
 		/*
 		 * We isolated non-lru movable page so here we can use
 		 * __PageMovable because LRU page's mapping cannot have
@@ -186,6 +184,8 @@ void putback_movable_pages(struct list_head *l)
 			put_page(page);
 		} else {
 			putback_lru_page(page);
+			dec_node_page_state(page, NR_ISOLATED_ANON +
+					page_is_file_cache(page));
 		}
 	}
 }
@@ -1121,8 +1121,15 @@ static ICE_noinline int unmap_and_move(new_page_t get_new_page,
 		 * restored.
 		 */
 		list_del(&page->lru);
-		dec_node_page_state(page, NR_ISOLATED_ANON +
-				page_is_file_cache(page));
+
+		/*
+		 * Compaction can migrate also non-LRU pages which are
+		 * not accounted to NR_ISOLATED_*. They can be recognized
+		 * as __PageMovable
+		 */
+		if (likely(!__PageMovable(page)))
+			dec_node_page_state(page, NR_ISOLATED_ANON +
+					page_is_file_cache(page));
 	}
 
 	/*

-- 
Michal Hocko
SUSE Labs